jetstream

by nats-io

nats-io / jetstream

JetStream Utilities

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JetStream (Technical Preview)

JetStream is the NATS.io persistence engine that will support streaming as well as traditional message and worker queues for At-Least-Once delivery semantics.

Contents

Concepts

In JetStream the configuration for storing messages is defined separately from how they are consumed. Storage is defined in a Stream and consuming messages is defined by multiple Consumers.

We'll discuss these 2 subjects in the context of this architecture.

Orders

While this is an incomplete architecture it does show a number of key points:

  • Many related subjects are stored in a Stream
  • Consumers can have different modes of operation and receive just subsets of the messages
  • Multiple Acknowledgement modes are supported

A new order arrives on

ORDERS.received
, gets sent to the
NEW
Consumer who, on success, will create a new message on
ORDERS.processed
. The
ORDERS.processed
message again enters the Stream where a
DISPATCH
Consumer receives it and once processed it will create an
ORDERS.completed
message which will again enter the Stream. These operations are all
pull
based meaning they are work queues and can scale horizontally. All require acknowledged delivery ensuring no order is missed.

All messages are delivered to a

MONITOR
Consumer without any acknowledgement and using Pub/Sub semantics - they are pushed to the monitor.

As messages are acknowledged to the

NEW
and
DISPATCH
Consumers, a percentage of them are Sampled and messages indicating redelivery counts, ack delays and more, are delivered to the monitoring system.

Streams

Streams define how messages are stored and retention duration. Streams consume normal NATS subjects, any message found on those subjects will be delivered to the defined storage system. You can do a normal publish to the subject for unacknowledged delivery, else if you send a Request to the subject the JetStream server will reply with an acknowledgement that it was stored.

As of January 2020, in the tech preview we have

file
and
memory
based storage systems, we do not yet support clustering.

In the diagram above we show the concept of storing all

ORDERS.*
in the Stream even though there are many types of order related messages. We'll show how you can selectively consume subsets of messages later. Relatively speaking the Stream is the most resource consuming component so being able to combine related data in this manner is important to consider.

Streams can consume many subjects. Here we have

ORDERS.*
but we could also consume
SHIPPING.state
into the same Stream should that make sense (not shown here).

Streams support various retention policies - they can be kept based on limits like max count, size or age but also more novel methods like keeping them as long as any Consumers have them unacknowledged, or work queue like behavior where a message is removed after first ack.

Streams support deduplication using a

Msg-Id
header and a sliding window within which to track duplicate messages. See the Message Deduplication section.

When defining Streams the items below make up the entire configuration of the set.

|Item|Description| |----|-----------| |MaxAge|Maximum age of any message in the stream, expressed in microseconds| |MaxBytes|How big the Stream may be, when the combined stream size exceeds this old messages are removed| |MaxMsgSize|The largest message that will be accepted by the Stream| |MaxMsgs|How many messages may be in a Stream, oldest messages will be removed if the Stream exceeds this size| |MaxConsumers|How many Consumers can be defined for a given Stream,

-1
for unlimited| |Name|A name for the Stream that may not have spaces, tabs or
.
| |NoAck|Disables acknowledging messages that are received by the Stream| |Replicas|How many replicas to keep for each message (not implemented as of January 2020)| |Retention|How message retention is considered,
LimitsPolicy
(default),
InterestPolicy
or
WorkQueuePolicy
| |Discard|When a Stream reached it's limits either,
DiscardNew
refuses new messages while
DiscardOld
(default) deletes old messages| |Storage|The type of storage backend,
file
and
memory
as of January 2020| |Subjects|A list of subjects to consume, supports wildcards| |Duplicates|The window within which to track duplicate messages|

Consumers

Each Consumer, or related group of Consumers, of a Stream will need an Consumer defined. It's ok to define thousands of these pointing at the same Stream.

Consumers can either be

push
based where JetStream will deliver the messages as fast as possible to a subject of your choice or
pull
based for typical work queue like behavior. The rate of message delivery in both cases is subject to
ReplayPolicy
. A
ReplayInstant
Consumer will receive all messages as fast as possible while a
ReplayOriginal
Consumer will receive messages at the rate they were received, which is great for replaying production traffic in staging.

In the orders example above we have 3 Consumers. The first two select a subset of the messages from the Stream by specifying a specific subject like

ORDERS.processed
. The Stream consumes
ORDERS.*
and this allows you to receive just what you need. The final Consumer receives all messages in a
push
fashion.

Consumers track their progress, they know what messages were delivered, acknowledged, etc., and will redeliver messages they sent that were not acknowledged. When first created, the Consumer has to know what message to send as the first one. You can configure either a specific message in the set (

StreamSeq
), specific time (
StartTime
), all (
DeliverAll
) or last (
DeliverLast
). This is the starting point and from there, they all behave the same - delivering all of the following messages with optional Acknowledgement.

Acknowledgements default to

AckExplicit
- the only supported mode for pull-based Consumers - meaning every message requires a distinct acknowledgement. But for push-based Consumers, you can set
AckNone
that does not require any acknowledgement, or
AckAll
which quite interestingly allows you to acknowledge a specific message, like message
100
, which will also acknowledge messages
1
through
99
. The
AckAll
mode can be a great performance boost.

Some messages may cause your applications to crash and cause a never ending loop forever poisoning your system. The

MaxDeliver
setting allow you to set a upper bound to how many times a message may be delivered.

To assist with creating monitoring applications, one can set a

SampleFrequency
which is a percentage of messages for which the system should sample and create events. These events will include delivery counts and ack waits.

When defining Consumers the items below make up the entire configuration of the Consumer:

|Item|Description| |----|-----------| |AckPolicy|How messages should be acknowledged,

AckNone
,
AckAll
or
AckExplicit
| |AckWait|How long to allow messages to remain un-acknowledged before attempting redelivery| |DeliverPolicy|The initial starting mode of the consumer,
DeliverAll
,
DeliverLast
,
DeliverNew
,
DeliverByStartSequence
or
DeliverByStartTime
| |DeliverySubject|The subject to deliver observed messages, when not set, a pull-based Consumer is created| |Durable|The name of the Consumer| |FilterSubject|When consuming from a Stream with many subjects, or wildcards, select only a specific incoming subjects, supports wildcards| |MaxDeliver|Maximum amount times a specific message will be delivered. Use this to avoid poison pills crashing all your services forever| |OptStartSeq|When first consuming messages from the Stream start at this particular message in the set| |ReplayPolicy|How messages are sent
ReplayInstant
or
ReplayOriginal
| |SampleFrequency|What percentage of acknowledgements should be samples for observability, 0-100| |OptStartTime|When first consuming messages from the Stream start with messages on or after this time| |RateLimit|The rate of message delivery in bits per second|

Configuration

The rest of this document introduces the

nats
utility, but for completeness and reference this is how you'd create the ORDERS scenario. We'll configure a 1 year retention for order related messages:
$ nats str add ORDERS --subjects "ORDERS.*" --ack --max-msgs=-1 --max-bytes=-1 --max-age=1y --storage file --retention limits --max-msg-size=-1 --discard=old
$ nats con add ORDERS NEW --filter ORDERS.received --ack explicit --pull --deliver all --max-deliver=-1 --sample 100
$ nats con add ORDERS DISPATCH --filter ORDERS.processed --ack explicit --pull --deliver all --max-deliver=-1 --sample 100
$ nats con add ORDERS MONITOR --filter '' --ack none --target monitor.ORDERS --deliver last --replay instant

Getting Started

This tech preview is limited to a single server and defaults to the global account. JetStream is NATS 2.0 aware and is scoped to accounts from a resource limit perspective. This is not the same as an individual server's resources, but may feel that way starting out. Don't worry, clustering is coming next but we wanted to get input early from the community.

Using Docker

The

synadia/jsm:latest
docker image contains both the JetStream enabled NATS Server and the
nats
utility this guide covers.

In one window start JetStream:

$ docker run -ti -p 4222:4222 --name jetstream synadia/jsm:latest server
[1] 2020/01/20 12:44:11.752465 [INF] Starting nats-server version 2.2.0-beta
[1] 2020/01/20 12:44:11.752694 [INF] Git commit [19dc3eb]
[1] 2020/01/20 12:44:11.752875 [INF] Starting JetStream
[1] 2020/01/20 12:44:11.753692 [INF] ----------- JETSTREAM (Beta) -----------
[1] 2020/01/20 12:44:11.753794 [INF]   Max Memory:      1.46 GB
[1] 2020/01/20 12:44:11.753822 [INF]   Max Storage:     1.00 TB
[1] 2020/01/20 12:44:11.753860 [INF]   Store Directory: "/tmp/jetstream"
[1] 2020/01/20 12:44:11.753893 [INF] ----------------------------------------
[1] 2020/01/20 12:44:11.753988 [INF] JetStream state for account "$G" recovered
[1] 2020/01/20 12:44:11.754148 [INF] Listening for client connections on 0.0.0.0:4222
[1] 2020/01/20 12:44:11.754279 [INF] Server id is NDYX5IMGF2YLX6RC4WLZA7T3JGHPZR2RNCCIFUQBT6C4TP27Z6ZIC73V
[1] 2020/01/20 12:44:11.754308 [INF] Server is ready

And in another log into the utilities:

$ docker run -ti --link jetstream synadia/jsm:latest

This shell has the

nats
utility and all other NATS cli tools used in the rest of this guide.

Now skip to the

Administer JetStream
section.

Using Docker with NGS

You can join a JetStream instance to your NGS account, first we need a credential for testing JetStream:

$ nsc add user -a YourAccount --name leafnode --expiry 1M

You'll get a credential file somewhere like

~/.nkeys/creds/synadia/YourAccount/leafnode.creds
, mount this file into the docker container for JetStream using
-v ~/.nkeys/creds/synadia/YourAccount/leafnode.creds:/leafnode.creds
.
$ docker run -ti -v ~/.nkeys/creds/synadia/YourAccount/leafnode.creds:/leafnode.creds --name jetstream synadia/jsm:latest server
[1] 2020/01/20 12:44:11.752465 [INF] Starting nats-server version 2.2.0-beta
...
[1] 2020/01/20 12:55:01.849033 [INF] Connected leafnode to "connect.ngs.global"

Your JSM shell will still connect locally, other connections in your NGS account can use JetStream at this point.

Using Source

You will also want to have installed from the nats.go repo the examples/tools such as nats-pub, nats-sub, nats-req and possibly nats-bench. One of the design goals of JetStream was to be native to core NATS, so even though we will most certainly add in syntactic sugar to clients to make them more appealing, for this tech preview we will be using plain old NATS.

You will need a copy of the nats-server source locally and will need to be in the jetstream branch.

$ git clone https://github.com/nats-io/nats-server.git
$ cd nats-server
$ git checkout master
$ go build
$ ls -l nats-server

Starting the server you can use the

-js
flag. This will setup the server to reasonably use memory and disk. This is a sample run on my machine. JetStream will default to 1TB of disk and 75% of available memory for now.
$ ./nats-server -js

[16928] 2019/12/04 19:16:29.596968 [INF] Starting nats-server version 2.2.0-beta [16928] 2019/12/04 19:16:29.597056 [INF] Git commit [not set] [16928] 2019/12/04 19:16:29.597072 [INF] Starting JetStream [16928] 2019/12/04 19:16:29.597444 [INF] ----------- JETSTREAM (Beta) ----------- [16928] 2019/12/04 19:16:29.597451 [INF] Max Memory: 96.00 GB [16928] 2019/12/04 19:16:29.597454 [INF] Max Storage: 1.00 TB [16928] 2019/12/04 19:16:29.597461 [INF] Store Directory: "/var/folders/m0/k03vs55n2b54kdg7jm66g27h0000gn/T/jetstream" [16928] 2019/12/04 19:16:29.597469 [INF] ---------------------------------------- [16928] 2019/12/04 19:16:29.597732 [INF] Listening for client connections on 0.0.0.0:4222 [16928] 2019/12/04 19:16:29.597738 [INF] Server id is NAJ5GKP5OBVISP5MW3BFAD447LMTIOAHFEWMH2XYWLL5STVGN3MJHTXQ [16928] 2019/12/04 19:16:29.597742 [INF] Server is ready

You can override the storage directory if you want.

$ ./nats-server -js -sd /tmp/test

[16943] 2019/12/04 19:20:00.874148 [INF] Starting nats-server version 2.2.0-beta [16943] 2019/12/04 19:20:00.874247 [INF] Git commit [not set] [16943] 2019/12/04 19:20:00.874273 [INF] Starting JetStream [16943] 2019/12/04 19:20:00.874605 [INF] ----------- JETSTREAM (Beta) ----------- [16943] 2019/12/04 19:20:00.874613 [INF] Max Memory: 96.00 GB [16943] 2019/12/04 19:20:00.874615 [INF] Max Storage: 1.00 TB [16943] 2019/12/04 19:20:00.874620 [INF] Store Directory: "/tmp/test/jetstream" [16943] 2019/12/04 19:20:00.874625 [INF] ---------------------------------------- [16943] 2019/12/04 19:20:00.874868 [INF] Listening for client connections on 0.0.0.0:4222 [16943] 2019/12/04 19:20:00.874874 [INF] Server id is NCR6KDDGWUU2FXO23WAXFY66VQE6JNWVMA24ALF2MO5GKAYFIMQULKUO [16943] 2019/12/04 19:20:00.874877 [INF] Server is ready

These options can also be set in your configuration file:

// enables jetstream, an empty block will enable and use defaults
jetstream {
    // jetstream data will be in /data/nats-server/jetstream
    store_dir: "/data/nats-server"

// 1GB
max_memory_store: 1073741824

// 10GB
max_file_store: 10737418240

}

Administration and Usage from the CLI

Once the server is running it's time to use the management tool. This can be downloaded from the GitHub Release Page or you can use the

synadia/jsm:latest
docker image.
$ nats --help
usage: nats []  [ ...]
NATS Management Utility

Flags: --help Show context-sensitive help (also try --help-long and --help-man). --version Show application version. -s, --server="localhost:4222" NATS servers --creds=CREDS User credentials --tlscert=TLSCERT TLS public certifcate --tlskey=TLSKEY TLS private key --tlsca=TLSCA TLS certifcate authority chain --timeout=2s Time to give JetStream to respond to queries

Commands: help [...] Show help. ...

We'll walk through the above scenario and introduce features of the CLI and of JetStream as we recreate the setup above.

Throughout this example, we'll show other commands like

nats pub
and
nats sub
to interact with the system. These are normal existing core NATS commands and JetStream is fully usable by only using core NATS.

We'll touch on some additional features but please review the section on the design model to understand all possible permutations.

Account Information

JetStream is multi-tenant so you will need to check that your account is enabled for JetStream and is not limited. You can view your limits as follows:

$ nats account info

  Memory: 0 B of 6.4 GB
 Storage: 0 B of 1.1 TB
 Streams: 1 of Unlimited

Streams

The first step is to set up storage for our

ORDERS
related messages, these arrive on a wildcard of subjects all flowing into the same Stream and they are kept for 1 year.

Creating

$ nats str add ORDERS
? Subjects to consume ORDERS.*
? Storage backend file
? Retention Policy Limits
? Discard Policy Old
? Message count limit -1
? Message size limit -1
? Maximum message age limit 1y
? Maximum individual message size [? for help] (-1) -1
Stream ORDERS was created

Information for Stream ORDERS

Configuration:

         Subjects: ORDERS.*
 Acknowledgements: true
        Retention: File - Limits
         Replicas: 1
 Maximum Messages: -1
    Maximum Bytes: -1
      Maximum Age: 8760h0m0s

Maximum Message Size: -1 Maximum Consumers: -1

Statistics:

        Messages: 0
           Bytes: 0 B
        FirstSeq: 0
         LastSeq: 0
Active Consumers: 0

You can get prompted interactively for missing information as above, or do it all on one command. Pressing

?
in the CLI will help you map prompts to CLI options:
$ nats str add ORDERS --subjects "ORDERS.*" --ack --max-msgs=-1 --max-bytes=-1 --max-age=1y --storage file --retention limits --max-msg-size=-1 --discard old

Additionally one can store the configuration in a JSON file, the format of this is the same as

$ nats str info ORDERS -j | jq .config
:
$ nats str add ORDERS --config orders.json

Listing

We can confirm our Stream was created:

$ nats str ls
Streams:

ORDERS

Querying

Information about the configuration of the Stream can be seen, and if you did not specify the Stream like below, it will prompt you based on all known ones:

$ nats str info ORDERS
Information for Stream ORDERS

Configuration:

         Subjects: ORDERS.*

No Acknowledgements: false Retention: File - Limits Replicas: 1 Maximum Messages: -1 Maximum Bytes: -1 Maximum Age: 8760h0m0s Maximum Consumers: -1

Statistics:

        Messages: 0
           Bytes: 0 B
        FirstSeq: 0
         LastSeq: 0
Active Consumers: 0

Most commands that show data as above support

-j
to show the results as JSON:
$ nats str info ORDERS -j
{
  "config": {
    "name": "ORDERS",
    "subjects": [
      "ORDERS.*"
    ],
    "retention": "limits",
    "max_consumers": -1,
    "max_msgs": -1,
    "max_bytes": -1,
    "max_age": 31536000000000000,
    "storage": "file",
    "num_replicas": 1
  },
  "stats": {
    "messages": 0,
    "bytes": 0,
    "first_seq": 0,
    "last_seq": 0,
    "consumer_count": 0
  }
}

This is the general pattern for the entire

nats
utility as it relates to JetStream - prompting for needed information but every action can be run non-interactively making it usable as a cli api. All information output like seen above can be turned into JSON using
-j
.

Copying

A stream can be copied into another, which also allows the configuration of the new one to be adjusted via CLI flags:

$ nats str cp ORDERS ARCHIVE --subjects "ORDERS_ARCVHIVE.*" --max-age 2y
Stream ORDERS was created

Information for Stream ARCHIVE

Configuration:

         Subjects: ORDERS_ARCVHIVE.*

... Maximum Age: 17520h0m0s ...

Editing

A stream configuration can be edited, which allows the configuration to be adjusted via CLI flags. Here I have a incorrectly created ORDERS stream that I fix:

$ nats str info ORDERS -j | jq .config.subjects
[
  "ORDERS.new"
]

$ nats str edit ORDERS --subjects "ORDERS.*" Stream ORDERS was updated

Information for Stream ORDERS

Configuration:

         Subjects: ORDERS.*

....

Additionally one can store the configuration in a JSON file, the format of this is the same as

$ nats str info ORDERS -j | jq .config
:
$ nats str edit ORDERS --config orders.json

Publishing Into a Stream

Now let's add in some messages to our Stream. You can use

nats pub
to add messages, pass the
--wait
flag to see the publish ack being returned.

You can publish without waiting for acknowledgement:

$ nats pub ORDERS.scratch hello
Published [sub1] : 'hello'

But if you want to be sure your messages got to JetStream and were persisted you can make a request:

$ nats req ORDERS.scratch hello
13:45:03 Sending request on [ORDERS.scratch]
13:45:03 Received on [_INBOX.M8drJkd8O5otORAo0sMNkg.scHnSafY]: '+OK'

Keep checking the status of the Stream while doing this and you'll see it's stored messages increase.

$ nats str info ORDERS
Information for Stream ORDERS
...
Statistics:

        Messages: 3
           Bytes: 147 B
        FirstSeq: 1
         LastSeq: 3
Active Consumers: 0

After putting some throw away data into the Stream, we can purge all the data out - while keeping the Stream active:

Deleting All Data

To delete all data in a stream use

purge
:
$ nats str purge ORDERS -f
...
Statistics:

        Messages: 0
           Bytes: 0 B
        FirstSeq: 1,000,001
         LastSeq: 1,000,000
Active Consumers: 0

Deleting A Message

A single message can be securely removed from the stream:

$ nats str rmm ORDERS 1 -f

Deleting Sets

Finally for demonstration purposes, you can also delete the whole Stream and recreate it so then we're ready for creating the Consumers:

$ nats str rm ORDERS -f
$ nats str add ORDERS --subjects "ORDERS.*" --ack --max-msgs=-1 --max-bytes=-1 --max-age=1y --storage file --retention limits --max-msg-size=-1

Consumers

Consumers is how messages are read or consumed from the Stream. We support pull and push-based Consumers and the example scenario has both, lets walk through that.

Creating Pull-Based Consumers

The

NEW
and
DISPATCH
Consumers are pull-based, meaning the services consuming data from them have to ask the system for the next available message. This means you can easily scale your services up by adding more workers and the messages will get spread across the workers based on their availability.

Pull-based Consumers are created the same as push-based Consumers, just don't specify a delivery target.

$ nats con ls ORDERS
No Consumers defined

We have no Consumers, lets add the

NEW
one:

I supply the

--sample
options on the CLI as this is not prompted for at present, everything else is prompted. The help in the CLI explains each:
$ nats con add --sample 100
? Select a Stream ORDERS
? Consumer name NEW
? Delivery target
? Start policy (all, last, 1h, msg sequence) all
? Filter Stream by subject (blank for all) ORDERS.received
? Maximum Allowed Deliveries 20
Information for Consumer ORDERS > NEW

Configuration:

    Durable Name: NEW
       Pull Mode: true
         Subject: ORDERS.received
     Deliver All: true
    Deliver Last: false
      Ack Policy: explicit
        Ack Wait: 30s
   Replay Policy: instant

Maximum Deliveries: 20 Sampling Rate: 100

State:

Last Delivered Message: Consumer sequence: 1 Stream sequence: 1 Acknowledgment floor: Consumer sequence: 0 Stream sequence: 0 Pending Messages: 0 Redelivered Messages: 0

This is a pull-based Consumer (empty Delivery Target), it gets messages from the first available message and requires specific acknowledgement of each and every message.

It only received messages that originally entered the Stream on

ORDERS.received
. Remember the Stream subscribes to
ORDERS.*
, this lets us select a subset of messages from the Stream.

A Maximum Delivery limit of 20 is set, this means if the message is not acknowledged it will be retried but only up to this maximum total deliveries.

Again this can all be done in a single CLI call, lets make the

DISPATCH
Consumer:
$ nats con add ORDERS DISPATCH --filter ORDERS.processed --ack explicit --pull --deliver all --sample 100 --max-deliver 20

Additionally one can store the configuration in a JSON file, the format of this is the same as

$ nats con info ORDERS DISPATCH -j | jq .config
:
$ nats con add ORDERS MONITOR --config monitor.json

Creating Push-Based Consumers

Our

MONITOR
Consumer is push-based, has no ack and will only get new messages and is not sampled:
$ nats con add
? Select a Stream ORDERS
? Consumer name MONITOR
? Delivery target monitor.ORDERS
? Start policy (all, last, 1h, msg sequence) last
? Acknowledgement policy none
? Replay policy instant
? Filter Stream by subject (blank for all)
? Maximum Allowed Deliveries -1
Information for Consumer ORDERS > MONITOR

Configuration:

  Durable Name: MONITOR

Delivery Subject: monitor.ORDERS Deliver All: false Deliver Last: true Ack Policy: none Replay Policy: instant

State:

Last Delivered Message: Consumer sequence: 1 Stream sequence: 3 Acknowledgment floor: Consumer sequence: 0 Stream sequence: 2 Pending Messages: 0 Redelivered Messages: 0

Again you can do this with a single non interactive command:

$ nats con add ORDERS MONITOR --ack none --target monitor.ORDERS --deliver last --replay instant --filter ''

Additionally one can store the configuration in a JSON file, the format of this is the same as

$ nats con info ORDERS MONITOR -j | jq .config
:
$ nats con add ORDERS --config monitor.json

Listing

You can get a quick list of all the Consumers for a specific Stream:

$ nats con ls ORDERS
Consumers for Stream ORDERS:

    DISPATCH
    MONITOR
    NEW

Querying

All details for an Consumer can be queried, lets first look at a pull-based Consumer:

$ nats con info ORDERS DISPATCH
Information for Consumer ORDERS > DISPATCH

Configuration:

  Durable Name: DISPATCH
     Pull Mode: true
       Subject: ORDERS.processed
   Deliver All: true
  Deliver Last: false
    Ack Policy: explicit
      Ack Wait: 30s
 Replay Policy: instant
 Sampling Rate: 100

State:

Last Delivered Message: Consumer sequence: 1 Stream sequence: 1 Acknowledgment floor: Consumer sequence: 0 Stream sequence: 0 Pending Messages: 0 Redelivered Messages: 0

More details about the

State
section will be shown later when discussing the ack models in depth.

Consuming Pull-Based Consumers

Pull-based Consumers require you to specifically ask for messages and ack them, typically you would do this with the client library

Request()
feature, but the
jsm
utility has a helper:

First we ensure we have a message:

$ nats pub ORDERS.processed "order 1"
$ nats pub ORDERS.processed "order 2"
$ nats pub ORDERS.processed "order 3"

We can now read them using

nats
:
$ nats con next ORDERS DISPATCH
--- received on ORDERS.processed
order 1

Acknowledged message

$ nats con next ORDERS DISPATCH --- received on ORDERS.processed order 2

Acknowledged message

You can prevent ACKs by supplying

--no-ack
.

To do this from code you'd send a

Request()
to
$JS.NEXT.ORDERS.DISPATCH
:
$ nats req '$JS.NEXT.ORDERS.DISPATCH' ''
Published [$JS.NEXT.ORDERS.DISPATCH] : ''
Received [ORDERS.processed] : 'order 3'

Here

nats req
cannot ack, but in your code you'd respond to the received message with a nil payload as an Ack to JetStream.

Consuming Push-Based Consumers

Push-based Consumers will publish messages to a subject and anyone who subscribes to the subject will get them, they support different Acknowledgement models covered later, but here on the

MONITOR
Consumer we have no Acknowledgement.
$ nats con info ORDERS MONITOR
...
  Delivery Subject: monitor.ORDERS
...

The Consumer is publishing to that subject, so lets listen there:

$ nats sub monitor.ORDERS
Listening on [monitor.ORDERS]
[#3] Received on [ORDERS.processed]: 'order 3'
[#4] Received on [ORDERS.processed]: 'order 4'

Note the subject here of the received message is reported as

ORDERS.processed
this helps you distinguish what you're seeing in a Stream covering a wildcard, or multiple subject, subject space.

This Consumer needs no ack, so any new message into the ORDERS system will show up here in real time.

Configuration Management

In many cases managing the configuration in your application code is the best model, many teams though wish to pre-create Streams and Consumers.

We support a number of tools to assist with this:

nats Admin CLI

The

nats
CLI can be used to manage Streams and Consumers easily using it's
--config
flag, for example:

Add a new Stream

This creates a new Stream based on

orders.json
. The
orders.json
file can be extracted from an existing stream using
nats stream info ORDERS -j | jq .config
$ nats str add ORDERS --config orders.json

Edit an existing Stream

This edits an existing stream ensuring it complies with the configuration in

orders.json
$ nats str edit ORDERS --config orders.json

Add a New Consumer

This creates a new Consumer based on

orders_new.json
. The
orders_new.json
file can be extracted from an existing stream using
nats con info ORDERS NEW -j | jq .config
$ nats con add ORDERS NEW --config orders_new.json

Terraform

Terraform is a Cloud configuration tool from Hashicorp found at terraform.io, we maintain a Provider for Terraform called terraform-provider-jetstream that can maintain JetStream using Terraform.

Setup

Our provider is not hosted by Hashicorp so installation is a bit more complex than typical. Browse to the Release Page and download the release for your platform and extract it into your Terraform plugins directory.

$ unzip -l terraform-provider-jetstream_0.0.2_darwin_amd64.zip
Archive:  terraform-provider-jetstream_0.0.2_darwin_amd64.zip
  Length      Date    Time    Name
---------  ---------- -----   ----
    11357  03-09-2020 10:48   LICENSE
     1830  03-09-2020 12:53   README.md
 24574336  03-09-2020 12:54   terraform-provider-jetstream_v0.0.2

Place the

terraform-provider-jetstream_v0.0.2
file in
~/.terraform.d/plugins/terraform-provider-jetstream_v0.0.2

In your project you can configure the Provider like this:

provider "jetstream" {
  servers = "connect.ngs.global"
  credentials = "ngs_jetstream_admin.creds"
}

And start using it, here's an example that create the

ORDERS
example. Review the Project README for full details.
resource "jetstream_stream" "ORDERS" {
  name     = "ORDERS"
  subjects = ["ORDERS.*"]
  storage  = "file"
  max_age  = 60 * 60 * 24 * 365
}

resource "jetstream_consumer" "ORDERS_NEW" { stream_id = jetstream_stream.ORDERS.id durable_name = "NEW" deliver_all = true filter_subject = "ORDERS.received" sample_freq = 100 }

resource "jetstream_consumer" "ORDERS_DISPATCH" { stream_id = jetstream_stream.ORDERS.id durable_name = "DISPATCH" deliver_all = true filter_subject = "ORDERS.processed" sample_freq = 100 }

resource "jetstream_consumer" "ORDERS_MONITOR" { stream_id = jetstream_stream.ORDERS.id durable_name = "MONITOR" deliver_last = true ack_policy = "none" delivery_subject = "monitor.ORDERS" }

output "ORDERS_SUBJECTS" { value = jetstream_stream.ORDERS.subjects }

GitHub Actions

We have a pack of GitHub Actions that let you manage an already running JetStream Server, useful for managing releases or standing up test infrastructure.

Full details and examples are in the jetstream-gh-actions repository, here's an example.

on: push
name: orders
jobs:

First we delete the ORDERS stream and consumer if they already exist

clean_orders: runs-on: ubuntu-latest steps: - name: orders_stream uses: nats-io/jetstream-gh-action/delete/[email protected] with: missing_ok: 1 stream: ORDERS server: js.example.net

Now we create the Stream and Consumers using the same configuration files the

nats CLI utility would use as shown above

create_orders: runs-on: ubuntu-latest needs: clean_orders steps: - uses: actions/[email protected] - name: orders_stream uses: nats-io/jetstream-gh-action/create/[email protected] with: config: ORDERS.json server: js.example.net - name: orders_new_consumer uses: nats-io/jetstream-gh-action/create/[email protected] with: config: ORDERS_NEW.json stream: ORDERS server: js.example.net

We publish a message to a specific Subject, perhaps some consumer is

waiting there for it to kick off tests

publish_message: runs-on: ubuntu-latest needs: create_orders steps: - uses: actions/[email protected] - name: orders_new_consumer uses: nats-io/[email protected] with: subject: ORDERS.deployment message: Published new deployment via "${{ github.event_name }}" in "${{ github.repository }}" server: js.example.net

Kubernetes JetStream Controller

The JetStream controllers allows you to manage NATS JetStream Streams and Consumers via K8S CRDs. You can find more info on how to deploy and usage here. Below you can find an example on how to create a stream and a couple of consumers:

---
apiVersion: jetstream.nats.io/v1beta1
kind: Stream
metadata:
  name: mystream
spec:
  name: mystream
  subjects: ["orders.*"]
  storage: memory
  maxAge: 1h
---
apiVersion: jetstream.nats.io/v1beta1
kind: Consumer
metadata:
  name: my-push-consumer
spec:
  streamName: mystream
  durableName: my-push-consumer
  deliverSubject: my-push-consumer.orders
  deliverPolicy: last
  ackPolicy: none
  replayPolicy: instant
---
apiVersion: jetstream.nats.io/v1beta1
kind: Consumer
metadata:
  name: my-pull-consumer
spec:
  streamName: mystream
  durableName: my-pull-consumer
  deliverPolicy: all
  filterSubject: orders.received
  maxDeliver: 20
  ackPolicy: explicit

Once the CRDs are installed you can use

kubectl
to manage the streams and consumers as follows:
$ kubectl get streams
NAME       STATE     STREAM NAME   SUBJECTS
mystream   Created   mystream      [orders.*]

$ kubectl get consumers NAME STATE STREAM CONSUMER ACK POLICY my-pull-consumer Created mystream my-pull-consumer explicit my-push-consumer Created mystream my-push-consumer none

If you end up in an Errored state, run kubectl describe for more info.

kubectl describe streams mystream

kubectl describe consumers my-pull-consumer

Disaster Recovery

Disaster Recovery of the JetStream system is a topic we are still exploring and fleshing out and that will be impacted by the clustering work. For example replication will extend the options available to you.

Today we have a few approaches to consider:

  • nats
    CLI + Configuration Backups + Data Snapshots
  • Configuration Management + Data Snapshots

Data Backup

In all scenarios you can perform data snapshots and restores over the NATS protocol. This is good if you do not manage the NATS servers hosting your data, and you wish to do a backup of your data.

The backup includes:

  • Stream configuration and state
  • Stream Consumer configuration and state
  • All data including metadata like timestamps and headers
$ nats stream backup ORDERS /data/js-backup/ORDERS.tgz
Starting backup of Stream "ORDERS" with 13 data blocks

2.4 MiB/s [====================================================================] 100%

Received 13 MiB bytes of compressed data in 3368 chunks for stream "ORDERS" in 1.223428188s, 813 MiB uncompressed

During the backup the Stream is in a state where it's configuration cannot change and no data will be expired from it based on Limits or Retention Policies.

Progress using the terminal bar can be disabled using

--no-progress
, it will then issue log lines instead.

Restoring Data

The backup made above can be restored into another server - but into the same Stream name.

$ nats str restore ORDERS /data/js-backup/ORDERS.tgz
Starting restore of Stream "ORDERS" from file "/data/js-backup/ORDERS.tgz"

13 MiB/s [====================================================================] 100%

Restored stream "ORDERS" in 937.071149ms

Information for Stream ORDERS

Configuration:

         Subjects: ORDERS.>

...

The

/data/js-backup/ORDERS.tgz
file can also be extracted into the data dir of a stopped NATS Server.

Progress using the terminal bar can be disabled using

--no-progress
, it will then issue log lines instead.

Interactive CLI

In environments where the

nats
CLI is used interactively to configure the server you do not have a desired state to recreate the server from. This is not the ideal way to administer the server, we recommend Configuration Management, but many will use this approach.

Here you can back up the configuration into a directory from where you can recover the configuration later. The data for File backed stores can also be backed up.

$ nats backup /data/js-backup
15:56:11 Creating JetStream backup into /data/js-backup
15:56:11 Stream ORDERS to /data/js-backup/stream_ORDERS.json
15:56:11 Consumer ORDERS > NEW to /data/js-backup/stream_ORDERS_consumer_NEW.json
15:56:11 Configuration backup complete

This backs up Stream, Consumer and Stream Template configuration.

During the same process the data can also be backed up by passing

--data
, this will create files like
/data/js-backup/stream_ORDERS.tgz
.

Later the data can be restored, for Streams we support editing the Stream configuration in place to match what was in the backup.

$ nats restore /tmp/backup --update-streams
15:57:42 Reading file /tmp/backup/stream_ORDERS.json
15:57:42 Reading file /tmp/backup/stream_ORDERS_consumer_NEW.json
15:57:42 Updating Stream ORDERS configuration
15:57:42 Restoring Consumer ORDERS > NEW

The

nats restore
tool does not support restoring data, the same process using
nats stream restore
, as outlined earlier, can be used which will also restore Stream and Consumer configurations and state.

Model Deep Dive

The Orders example touched on a lot of features, but some like different Ack models and message limits, need a bit more detail. This section will expand on the above and fill in some blanks.

Stream Limits, Retention Modes and Discard Policy

Streams store data on disk, but we cannot store all data forever so we need ways to control their size automatically.

There are 3 features that come into play when Streams decide how long they store data.

The

Retention Policy
describes based on what criteria a set will evict messages from its storage:

|Retention Policy|Description| |----------------|-----------| |

LimitsPolicy
|Limits are set for how many messages, how big the storage and how old messages may be| |
WorkQueuePolicy
|Messages are kept until they were consumed by any one single observer and then removed| |
InterestPolicy
|Messages are kept as long as there are Consumers active for them|

In all Retention Policies the basic limits apply as upper bounds, these are

MaxMsgs
for how many messages are kept in total,
MaxBytes
for how big the set can be in total and
MaxAge
for what is the oldest message that will be kept. These are the only limits in play with
LimitsPolicy
retention.

One can then define additional ways a message may be removed from the Stream earlier than these limits. In

WorkQueuePolicy
the messages will be removed as soon as any Consumer received an Acknowledgement. In
InterestPolicy
messages will be removed as soon as there are no more Consumers.

In both

WorkQueuePolicy
and
InterestPolicy
the age, size and count limits will still apply as upper bounds.

A final control is the Maximum Size any single message may have. NATS have it's own limit for maximum size (1 MiB by default), but you can say a Stream will only accept messages up to 1024 bytes using

MaxMsgSize
.

The

Discard Policy
sets how messages are discard when limits set by
LimitsPolicy
are reached. The
DiscardOld
option removes old messages making space for new, while
DiscardNew
refuses any new messages.

The

WorkQueuePolicy
mode is a specialized mode where a message, once consumed and acknowledged, is discarded from the Stream. In this mode there are a few limits on consumers. Inherently it's about 1 message to one consumer, this means you cannot have overlapping consumers defined on the Stream - needs unique filter subjects.

Message Deduplication

JetStream support idempotent message writes by ignoring duplicate messages as indicated by the

Msg-Id
header.
% nats req -H Msg-Id:1 ORDERS.new hello1
% nats req -H Msg-Id:1 ORDERS.new hello2
% nats req -H Msg-Id:1 ORDERS.new hello3
% nats req -H Msg-Id:1 ORDERS.new hello4

Here we set a

Msg-Id:1
header which tells JetStream to ensure we do not have duplicates of this message - we only consult the message ID not the body.
$ nats str info ORDERS
....
State:

        Messages: 1
           Bytes: 67 B

The default window to track duplicates in is 2 minutes, this can be set on the command line using

--dupe-window
when creating a stream, though we would caution against large windows.

Acknowledgement Models

Streams support acknowledging receiving a message, if you send a

Request()
to a subject covered by the configuration of the Stream the service will reply to you once it stored the message. If you just publish, it will not. A Stream can be set to disable Acknowledgements by setting
NoAck
to
true
in it's configuration.

Consumers have 3 acknowledgement modes:

|Mode|Description| |----|-----------| |

AckExplicit
|This requires every message to be specifically acknowledged, it's the only supported option for pull-based Consumers| |
AckAll
|In this mode if you acknowledge message
100
it will also acknowledge message
1
-
99
, this is good for processing batches and to reduce ack overhead| |
AckNone
|No acknowledgements are supported|

To understand how Consumers track messages we will start with a clean

ORDERS
Stream and
DISPATCH
Consumer.
$ nats str info ORDERS
...
Statistics:

        Messages: 0
           Bytes: 0 B
        FirstSeq: 0
         LastSeq: 0
Active Consumers: 1

The Set is entirely empty

$ nats con info ORDERS DISPATCH
...
State:

Last Delivered Message: Consumer sequence: 1 Stream sequence: 1 Acknowledgment floor: Consumer sequence: 0 Stream sequence: 0 Pending Messages: 0 Redelivered Messages: 0

The Consumer has no messages oustanding and has never had any (Consumer sequence is 1).

We publish one message to the Stream and see that the Stream received it:

$ nats pub ORDERS.processed "order 4"
Published 7 bytes to ORDERS.processed
$ nats str info ORDERS
...
Statistics:

        Messages: 1
           Bytes: 53 B
        FirstSeq: 1
         LastSeq: 1
Active Consumers: 1

As the Consumer is pull-based, we can fetch the message, ack it, and check the Consumer state:

$ nats con next ORDERS DISPATCH
--- received on ORDERS.processed
order 4

Acknowledged message

$ nats con info ORDERS DISPATCH ... State:

Last Delivered Message: Consumer sequence: 2 Stream sequence: 2 Acknowledgment floor: Consumer sequence: 1 Stream sequence: 1 Pending Messages: 0 Redelivered Messages: 0

The message got delivered and acknowledged -

Acknowledgement floor
is
1
and
1
, the sequence of the Consumer is
2
which means its had only the one message through and got acked. Since it was acked, nothing is pending or redelivering.

We'll publish another message, fetch it but not Ack it this time and see the status:

$ nats pub ORDERS.processed "order 5"
Published 7 bytes to ORDERS.processed

$ nats con next ORDERS DISPATCH --no-ack --- received on ORDERS.processed order 5

$ nats con info ORDERS DISPATCH State:

Last Delivered Message: Consumer sequence: 3 Stream sequence: 3 Acknowledgment floor: Consumer sequence: 1 Stream sequence: 1 Pending Messages: 1 Redelivered Messages: 0

Now we can see the Consumer have processed 2 messages (obs sequence is 3, next message will be 3) but the Ack floor is still 1 - thus 1 message is pending acknowledgement. Indeed this is confirmed in the

Pending messages
.

If I fetch it again and again do not ack it:

$ nats con next ORDERS DISPATCH --no-ack
--- received on ORDERS.processed
order 5

$ nats con info ORDERS DISPATCH State:

Last Delivered Message: Consumer sequence: 4 Stream sequence: 3 Acknowledgment floor: Consumer sequence: 1 Stream sequence: 1 Pending Messages: 1 Redelivered Messages: 1

The Consumer sequence increases - each delivery attempt increase the sequence - and our redelivered count also goes up.

Finally if I then fetch it again and ack it this time:

$ nats con next ORDERS DISPATCH 
--- received on ORDERS.processed
order 5

Acknowledged message $ nats con info ORDERS DISPATCH State:

Last Delivered Message: Consumer sequence: 5 Stream sequence: 3 Acknowledgment floor: Consumer sequence: 1 Stream sequence: 1 Pending Messages: 0 Redelivered Messages: 0

Having now Acked the message there are no more pending.

Additionally there are a few types of acknowledgements:

|Type|Bytes|Description| |----|-----|-----------| |

AckAck
|nil,
+ACK
|Acknowledges a message was completely handled| |
AckNak
|
-NAK
|Signals that the message will not be processed now and processing can move onto the next message, NAK'd message will be retried| |
AckProgress
|
+WPI
|When sent before the AckWait period indicates that work is ongoing and the period should be extended by another equal to
AckWait
| |
AckNext
|
+NXT
|Acknowledges the message was handled and requests delivery of the next message to the reply subject. Only applies to Pull-mode.| |
AckTerm
|
+TERM
|Instructs the server to stop redelivery of a message without acknowledging it as successfully processed|

So far all the examples was the

AckAck
type of acknowledgement, by replying to the Ack with the body as indicated in
Bytes
you can pick what mode of acknowledgement you want.

All of these acknowledgement modes support double acknowledgement - if you set a reply subject when acknowledging the server will in turn acknowledge having received your ACK.

Exactly Once Delivery

JetStream supports Exactly Once delivery by combining Message Deduplication and double acks.

On the publishing side you can avoid duplicate message ingestion using the Message Deduplication feature.

Consumers can be 100% sure a message was correctly processed by requesting the server Acknowledge having received your acknowledgement by setting a reply subject on the Ack. If you receive this response you will never receive that message again.

Consumer Starting Position

When setting up an Consumer you can decide where to start, the system supports the following for the

DeliverPolicy
:

|Policy|Description| |------|-----------| |

all
|Delivers all messages that are available| |
last
|Delivers the latest message, like a
tail -n 1 -f
| |
new
|Delivers only new messages that arrive after subscribe time| |
by_start_time
|Delivers from a specific time onward. Requires
OptStartTime
to be set| |
by_start_sequence
|Delivers from a specific stream sequence. Requires
OptStartSeq
to be set|

Regardless of what mode you set, this is only the starting point. Once started it will always give you what you have not seen or acknowledged. So this is merely how it picks the very first message.

Lets look at each of these, first we make a new Stream

ORDERS
and add 100 messages to it.

Now create a

DeliverAll
pull-based Consumer:
$ nats con add ORDERS ALL --pull --filter ORDERS.processed --ack none --replay instant --deliver all 
$ nats con next ORDERS ALL
--- received on ORDERS.processed
order 1

Acknowledged message

Now create a

DeliverLast
pull-based Consumer:
$ nats con add ORDERS LAST --pull --filter ORDERS.processed --ack none --replay instant --deliver last
$ nats con next ORDERS LAST
--- received on ORDERS.processed
order 100

Acknowledged message

Now create a

MsgSetSeq
pull-based Consumer:
$ nats con add ORDERS TEN --pull --filter ORDERS.processed --ack none --replay instant --deliver 10
$ nats con next ORDERS TEN
--- received on ORDERS.processed
order 10

Acknowledged message

And finally a time-based Consumer. Let's add some messages a minute apart:

$ nats str purge ORDERS
$ for i in 1 2 3
do
  nats pub ORDERS.processed "order ${i}"
  sleep 60
done

Then create an Consumer that starts 2 minutes ago:

$ nats con add ORDERS 2MIN --pull --filter ORDERS.processed --ack none --replay instant --deliver 2m
$ nats con next ORDERS 2MIN
--- received on ORDERS.processed
order 2

Acknowledged message

Ephemeral Consumers

So far, all the Consumers you have seen were Durable, meaning they exist even after you disconnect from JetStream. In our Orders scenario, though the

MONITOR
Consumer could very well be a short-lived thing there just while an operator is debugging the system, there is no need to remember the last seen position if all you are doing is wanting to observe the real-time state.

In this case, we can make an Ephemeral Consumer by first subscribing to the delivery subject, then creating a durable and giving it no durable name. An Ephemeral Consumer exists as long as any subscription is active on its delivery subject. It is automatically be removed, after a short grace period to handle restarts, when there are no subscribers.

Ephemeral Consumers can only be push-based.

Terminal 1:

$ nats sub my.monitor

Terminal 2:

$ nats con add ORDERS --filter '' --ack none --target 'my.monitor' --deliver last --replay instant --ephemeral

The

--ephemeral
switch tells the system to make an Ephemeral Consumer.

Consumer Message Rates

Typically what you want is if a new Consumer is made the selected messages are delivered to you as quickly as possible. You might want to replay messages at the rate they arrived though, meaning if messages first arrived 1 minute apart and you make a new Consumer it will get the messages a minute apart.

This is useful in load testing scenarios etc. This is called the

ReplayPolicy
and have values of
ReplayInstant
and
ReplayOriginal
.

You can only set

ReplayPolicy
on push-based Consumers.
$ nats con add ORDERS REPLAY --target out.original --filter ORDERS.processed --ack none --deliver all --sample 100 --replay original
...
     Replay Policy: original
...

Now lets publish messages into the Set 10 seconds apart:

$ for i in 1 2 3                                                                                                                                                      <15:15:35
do
  nats pub ORDERS.processed "order ${i}"
  sleep 10
done
Published [ORDERS.processed] : 'order 1'
Published [ORDERS.processed] : 'order 2'
Published [ORDERS.processed] : 'order 3'

And when we consume them they will come to us 10 seconds apart:

$ nats sub -t out.original
Listening on [out.original]
2020/01/03 15:17:26 [#1] Received on [ORDERS.processed]: 'order 1'
2020/01/03 15:17:36 [#2] Received on [ORDERS.processed]: 'order 2'
2020/01/03 15:17:46 [#3] Received on [ORDERS.processed]: 'order 3'
^C

Stream Templates

When you have many similar streams it can be helpful to auto create them, lets say you have a service by client and they are on subjects

CLIENT.*
, you can construct a template that will auto generate streams for any matching traffic.
$ nats str template add CLIENTS --subjects "CLIENT.*" --ack --max-msgs=-1 --max-bytes=-1 --max-age=1y --storage file --retention limits --max-msg-size 2048 --max-streams 1024 --discard old
Stream Template CLIENTS was created

Information for Stream Template CLIENTS

Configuration:

         Subjects: CLIENT.*
 Acknowledgements: true
        Retention: File - Limits
         Replicas: 1
 Maximum Messages: -1
    Maximum Bytes: -1
      Maximum Age: 8760h0m0s

Maximum Message Size: 2048 Maximum Consumers: -1 Maximum Streams: 1024

Managed Streams:

No Streams have been defined by this template

You can see no streams currently exist, let's publish some data:

$ nats pub CLIENT.acme hello

And we'll have 1 new Stream:

$ nats str ls
Streams:

    CLIENTS_acme

When the template is deleted all the streams it created will be deleted too.

Ack Sampling

In the earlier sections we saw that samples are being sent to a monitoring system. Let's look at that in depth; how the monitoring system works and what it contains.

As messages pass through an Consumer you'd be interested in knowing how many are being redelivered and how many times but also how long it takes for messages to be acknowledged.

Consumers can sample Ack'ed messages for you and publish samples so your monitoring system can observe the health of an Consumer. We will add support for this to NATS Surveyor.

Configuration

You can configure an Consumer for sampling by passing the

--sample 80
option to
nats consumer add
, this tells the system to sample 80% of Acknowledgements.

When viewing info of an Consumer you can tell if it's sampled or not:

$ nats con info ORDERS NEW
...
     Sampling Rate: 100
...

Consuming

Samples are published to

$JS.EVENT.METRIC.CONSUMER_ACK..
in JSON format containing
api.ConsumerAckMetric
. Use the
nats con events
command to view samples:
$ nats con events ORDERS NEW
Listening for Advisories on $JS.EVENT.ADVISORY.*.ORDERS.NEW
Listening for Metrics on $JS.EVENT.METRIC.*.ORDERS.NEW

15:08:31] [Ph0fsiOKRg1TS0c2k0mMz2] Acknowledgement Sample Consumer: ORDERS > NEW Stream Sequence: 40 Consumer Sequence: 161 Deliveries: 1 Delay: 1.009ms

$ nats con events ORDERS NEW --json
{
  "stream": "ORDERS",
  "consumer": "NEW",
  "consumer_seq": 155,
  "stream_seq": 143,
  "ack_time": 5387000,
  "delivered": 1
}
{
  "stream": "ORDERS",
  "consumer": "NEW",
  "consumer_seq": 156,
  "stream_seq": 144,
  "ack_time": 5807800,
  "delivered": 1
}

Storage Overhead

JetStream file storage is very efficient storing as little extra information about the message as possible.

NOTE: This might change once clustering is supported.

We do store some message data with each message, namely:

  • Message headers
  • The subject it was received on
  • The time it was received
  • The message payload
  • A hash of the message
  • The message sequence
  • A few other bits like length of the subject and lengh of headers

Without any headers the size is:

length of the message record (4bytes) + seq(8) + ts(8) + subj_len(2) + subj + msg + hash(8)

A 5 byte

hello
message without headers will take 39 bytes.

With headers:

length of the message record (4bytes) + seq(8) + ts(8) + subj_len(2) + subj + hdr_len(4) + hdr + msg + hash(8)

So if you are publishing many small messages the overhead will be, relatively speaking, quite large, but for larger messages the overhead is very small. If you publish many small messages it's worth trying to optimise the subject length.

NATS API Reference

Thus far we saw a lot of CLI interactions. The CLI works by sending and receiving specially crafted messages over core NATS to configure the JetStream system. In time we will look to add file based configuration but for now the only method is the NATS API.

NOTE: Some NATS client libraries may need to enable an option to use old style requests when interacting withe JetStream server. Consult the libraries README's for more information.

Reference

All of these subjects are found as constants in the NATS Server source, so for example the

$JS.API.STREAM.LIST
is a constant in the nats-server source
api.JetStreamListStreams
tables below will reference these constants and likewise data structures in the server for payloads.

Error Handling

The APIs used for administrative tools all respond with standardised JSON and these include errors.

$ nats req '$JS.API.STREAM.INFO.nonexisting' ''
Published 11 bytes to $JS.API.STREAM.INFO.nonexisting
Received  [_INBOX.lcWgjX2WgJLxqepU0K9pNf.mpBW9tHK] : {
  "type": "io.nats.jetstream.api.v1.stream_info_response",
  "error": {
    "code": 404,
    "description": "stream not found"
  }
}
$ nats req '$JS.STREAM.INFO.ORDERS' ''
Published 6 bytes to $JS.STREAM.INFO.ORDERS
Received  [_INBOX.fwqdpoWtG8XFXHKfqhQDVA.vBecyWmF] : '{
  "type": "io.nats.jetstream.api.v1.stream_info_response",
  "config": {
    "name": "ORDERS",
  ...
}

Here the responses include a

type
which can be used to find the JSON Schema for each response.

Non admin APIs - like those for adding a message to the stream will respond with

-ERR
or
+OK
with an optional reason after.

Admin API

All the admin actions the

nats
CLI can do falls in the sections below. The API structure are kept in the
api
package in the
jsm.go
repository.

Subjects that and in

T
like
api.JSApiConsumerCreateT
are formats and would need to have the Stream Name and in some cases also the Consumer name interpolated into them. In this case
t := fmt.Sprintf(api.JSApiConsumerCreateT, streamName)
to get the final subject.

The command

nats events
will show you an audit log of all API access events which includes the full content of each admin request, use this to view the structure of messages the
nats
command sends.

The API uses JSON for inputs and outputs, all the responses are typed using a

type
field which indicates their Schema. A JSON Schema repository can be found in
nats-io/jetstream/schemas
.

General Info

|Subject|Constant|Description|Request Payload|Response Payload| |-------|--------|-----------|---------------|----------------| |

$JS.API.INFO
|
api.JSApiAccountInfo
|Retrieves stats and limits about your account|empty payload|
api.JetStreamAccountStats
|

Streams

|Subject|Constant|Description|Request Payload|Response Payload| |-------|--------|-----------|---------------|----------------| |

$JS.API.STREAM.LIST
|
api.JSApiStreamList
|Paged list known Stream including all their current information|
api.JSApiStreamListRequest
|
api.JSApiStreamListResponse
| |
$JS.API.STREAM.CREATE.*
|
api.JSApiStreamCreateT
|Creates a new Stream|
api.StreamConfig
|
api.JSApiStreamCreateResponse
| |
$JS.API.STREAM.UPDATE.*
|
api.JSApiStreamUpdateT
|Updates an existing Stream with new config|
api.StreamConfig
|
api.JSApiStreamUpdateResponse
| |
$JS.API.STREAM.INFO.*
|
api.JSApiStreamInfoT
|Information about config and state of a Stream|empty payload, Stream name in subject|
api.JSApiStreamInfoResponse
| |
$JS.API.STREAM.DELETE.*
|
api.JSApiStreamDeleteT
|Deletes a Stream and all its data|empty payload, Stream name in subject|
api.JSApiStreamDeleteResponse
| |
$JS.API.STREAM.PURGE.*
|
api.JSApiStreamPurgeT
|Purges all of the data in a Stream, leaves the Stream|empty payload, Stream name in subject|
api.JSApiStreamPurgeResponse
| |
$JS.API.STREAM.MSG.DELETE.*
|
api.JSApiMsgDeleteT
|Deletes a specific message in the Stream by sequence, useful for GDPR compliance|
api.JSApiMsgDeleteRequest
|
api.JSApiMsgDeleteResponse
| |
$JS.API.STREAM.MSG.GET.*
|
api.JSApiMsgGetT
|Retrieves a specific message from the stream|
api.JSApiMsgGetRequest
|
api.JSApiMsgGetResponse
| |
$JS.API.STREAM.SNAPSHOT.*
|
api.JSApiStreamSnapshotT
|Initiates a streaming backup of a streams data|
api.JSApiStreamSnapshotRequest
|
api.JSApiStreamSnapshotResponse
| |
$JS.API.STREAM.RESTORE.*
|
api.JSApiStreamRestoreT
|Initiates a streaming restore of a stream|
{}
|
api.JSApiStreamRestoreResponse
|

Stream Templates

|Subject|Constant|Description|Request Payload|Response Payload| |-------|--------|-----------|---------------|----------------| |

$JS.API.STREAM.TEMPLATE.CREATE.*
|
api.JSApiTemplateCreateT
|Creates a Stream Template|
api.StreamTemplateConfig
|
api.JSApiStreamTemplateCreateResponse
| |
$JS.API.STREAM.TEMPLATE.NAMES
|
api.JSApiTemplateNames
|Paged list all known templates|
api.JSApiStreamTemplateNamesRequest
|
api.JSApiStreamTemplateNamesResponse
| |
$JS.API.STREAM.TEMPLATE.INFO.*
|
api.JSApiTemplateInfoT
|Information about the config and state of a Stream Template|empty payload, Template name in subject|
api.JSApiStreamTemplateInfoResponse
| |
$JS.API.STREAM.TEMPLATE.DELETE.*
|
api.JSApiTemplateDeleteT
|Delete a specific Stream Template and all streams created by this template|empty payload, Template name in subject|
api.JSApiStreamTemplateDeleteResponse
|

Consumers

|Subject|Constant|Description|Request Payload|Response Payload| |-------|--------|-----------|---------------|----------------| |

$JS.API.CONSUMER.CREATE.*
|
api.JSApiConsumerCreateT
|Create an ephemeral Consumer|
api.ConsumerConfig
, Stream name in subject|
api.JSApiConsumerCreateResponse
| |
$JS.API.CONSUMER.DURABLE.CREATE.*
|
api.JSApiDurableCreateT
|Create an Consumer|
api.ConsumerConfig
, Stream name in subject|
api.JSApiConsumerCreateResponse
| |
$JS.API.CONSUMER.LIST.*
|
api.JSApiConsumerListT
|Paged list of known Consumers including their current info|
api.JSApiConsumerListRequest
|
api.JSApiConsumerListResponse
| |
$JS.API.CONSUMER.NAMES.*
|
api.JSApiConsumerNamesT
|Paged list of known Consumer names|
api.JSApiConsumerNamesRequest
|
api.JSApiConsumerNamesResponse
| |
$JS.API.CONSUMER.INFO.*.*
|
api.JSApiConsumerInfoT
|Information about an Consumer|empty payload, Stream and Consumer names in subject|
api.JSApiConsumerInfoResponse
| |
$JS.API.CONSUMER.DELETE.*.*
|
api.JSApiConsumerDeleteT
|Deletes an Consumer|empty payload, Stream and Consumer names in subject|
api.JSApiConsumerDeleteResponse
|

ACLs

It's hard to notice here but there is a clear pattern in these subjects, lets look at the various JetStream related subjects:

General information

$JS.API.INFO

Stream and Consumer Admin

$JS.API.STREAM.CREATE.
$JS.API.STREAM.UPDATE.
$JS.API.STREAM.DELETE.
$JS.API.STREAM.INFO.
$JS.API.STREAM.PURGE.
$JS.API.STREAM.LIST
$JS.API.STREAM.NAMES
$JS.API.STREAM.MSG.DELETE.
$JS.API.STREAM.MSG.GET.
$JS.API.STREAM.SNAPSHOT.
$JS.API.STREAM.RESTORE.
$JS.API.CONSUMER.CREATE.
$JS.API.CONSUMER.DURABLE.CREATE..
$JS.API.CONSUMER.DELETE..
$JS.API.CONSUMER.INFO..
$JS.API.CONSUMER.LIST.
$JS.API.CONSUMER.MSG.NEXT..
$JS.API.CONSUMER.NAMES.
$JS.API.STREAM.TEMPLATE.CREATE.
$JS.API.STREAM.TEMPLATE.DELETE.
$JS.API.STREAM.TEMPLATE.INFO.
$JS.API.STREAM.TEMPLATE.NAMES

Stream and Consumer Use

$JS.API.CONSUMER.MSG.NEXT..
$JS.ACK...x.x.x
$JS.SNAPSHOT.ACK..
$JS.SNAPSHOT.RESTORE..

Events and Advisories:

$JS.EVENT.METRIC.CONSUMER_ACK..
$JS.EVENT.ADVISORY.MAX_DELIVERIES..

This allow you to easily create ACL rules that limit users to a specific Stream or Consumer and to specific verbs for administration purposes. For ensuring only the receiver of a message can Ack it we have response permissions ensuring you can only Publish to Response subject for messages you received.

Acknowledging Messages

Messages that need acknowledgement will have a Reply subject set, something like

$JS.ACK.ORDERS.test.1.2.2
, this is the prefix defined in
api.JetStreamAckPre
followed by
....
.

In all the Synadia maintained API's you can simply do

msg.Respond(nil)
(or language equivalent) which will send nil to the reply subject.

Fetching The Next Message From a Pull-based Consumer

If you have a pull-based Consumer you can send a standard NATS Request to

$JS.API.CONSUMER.MSG.NEXT..
, here the format is defined in
api.JetStreamRequestNextT
and requires populating using
fmt.Sprintf()
.
$ nats req '$JS.API.CONSUMER.MSG.NEXT.ORDERS.test' '1'
Published 1 bytes to $JS.API.CONSUMER.MSG.NEXT.ORDERS.test
Received  [js.1] : 'message 1'

Here we ask for just 1 message -

nats req
only shows 1 - but you can fetch a batch of messages by varying the argument. This combines well with the
AckAll
Ack policy.

Fetching From a Stream By Sequence

If you know the Stream sequence of a message you can fetch it directly, this does not support acks. Do a Request() to

$JS.API.STREAM.MSG.GET.ORDERS
sending it the message sequence as payload. Here the prefix is defined in
api.JetStreamMsgBySeqT
which also requires populating using
fmt.Sprintf()
.
$ nats req '$JS.API.STREAM.MSG.GET.ORDERS' '{"seq": 1}'
Published 1 bytes to $JS.STREAM.ORDERS.MSG.BYSEQ
Received  [_INBOX.cJrbzPJfZrq8NrFm1DsZuH.k91Gb4xM] : '{
  "type": "io.nats.jetstream.api.v1.stream_msg_get_response",
  "message": {
    "subject": "x",
    "seq": 1,
    "data": "aGVsbG8=",
    "time": "2020-05-06T13:18:58.115424+02:00"
  }
}'

The Subject shows where the message was received, Data is base64 encoded and Time is when it was received.

Consumer Samples

Samples are published to a specific subject per Consumer, something like

$JS.EVENT.METRIC.CONSUMER_ACK..
you can just subscribe to that and get
api.ConsumerAckMetric
messages in JSON format. The prefix is defined in
api.JetStreamMetricConsumerAckPre
.

Multi Tenancy and Resource Management

JetStream is compatible with NATS 2.0 Multi Tenancy using Accounts. A JetStream enabled server supports creating fully isolated JetStream environments for different accounts.

To enable JetStream in a server we have to configure it at the top level first:

jetstream: enabled

This will dynamically determine the available resources. It's recommended that you set specific limits though:

jetstream {
    store_dir: /data/jetstream
    max_mem: 1G
    max_file: 100G
}

At this point JetStream will be enabled and if you have a server that does not have accounts enabled all users in the server would have access to JetStream

jetstream {
    store_dir: /data/jetstream
    max_mem: 1G
    max_file: 100G
}

accounts { HR: { jetstream: enabled } }

Here the

HR
account would have access to all the resources configured on the server, we can restrict it:
jetstream {
    store_dir: /data/jetstream
    max_mem: 1G
    max_file: 100G
}

accounts { HR: { jetstream { max_mem: 512M max_file: 1G max_streams: 10 max_consumers: 100 } } }

Now the

HR
account it limited in various dimensions.

If you try to configure JetStream for an account without enabling it globally you'll get a warning and the account designated as System cannot have JetStream enabled.

nats
CLI

As part of the JetStream efforts a new

nats
CLI is being developed to act as a single point of access to the NATS eco system.

This CLI has been seen throughout the guide, it's available in the Docker containers today and downloadable on the Releases page.

Configuration Contexts

The CLI has a number of environment configuration settings - where your NATS server is, credentials, TLS keys and more:

$ nats --help
...
  -s, --server=NATS_URL         NATS servers
      --user=NATS_USER          Username of Token
      --password=NATS_PASSWORD  Password
      --creds=NATS_CREDS        User credentials
      --nkey=NATS_NKEY          User NKEY
      --tlscert=NATS_CERT       TLS public certificate
      --tlskey=NATS_KEY         TLS private key
      --tlsca=NATS_CA           TLS certificate authority chain
      --timeout=NATS_TIMEOUT    Time to wait on responses from NATS
      --context=CONTEXT         NATS Configuration Context to use for access
...

You can set these using the CLI flag, the environmet variable - like NATS_URL - or using our context feature.

A context is a named configuration that stores all these settings, you can switch between access configurations and designate a default.

Creating one is easy, just specify the same settings to the

nats context save
$ nats context save example --server nats://nats.example.net:4222 --description 'Example.Net Server'
$ nats context save local --server nats://localhost:4222 --description 'Local Host' --select 
$ nats context ls
Known contexts:

example Example.Net Server local* Local Host

We passed

--select
to the
local
one meaning it will be the default when nothing is set.
$ nats rtt
nats://localhost:4222:

nats://127.0.0.1:4222: 245.115µs nats://[::1]:4222: 390.239µs

$ nats rtt --context example nats://nats.example.net:4222:

nats://192.0.2.10:4222: 41.560815ms nats://192.0.2.11:4222: 41.486609ms nats://192.0.2.12:4222: 41.178009ms

The

nats context select
command can be used to set the default context.

All

nats
commands are context aware and the
nats context
command has various commands to view, edit and remove contexts.

Next Steps

There is plenty more to discuss and features to describe. We will continue to add information to this document and feel free to post any questions on the JetStream Slack channel. For the brave, take a look at

nats-server/test/jetstream_test.go
for all that JetStream can do. And please file any issues or communicate on Slack or by email [email protected].

Next up is a deep dive into the clustering implementation which will be completed before an official beta. The design has been ongoing since the beginning of coding but I wanted to get this out to the community to gather feedback and additional input.

Discussion Items

There a few items we are still considering/thinking about and would love the community's input. In no particular order.

DLQ (Dead Letter Queue)

Do we need or desire these? JetStream separates Streams (producing, retaining and ordering) from the Consumers (consumption). We do indicate the amount of times a message has been delivered and at least it may make sense when creating an Consumer to set a maximum for number of delivery attempts. Once that is reached however it is not clear what to do with the message. If the Stream is limit-based retention, the message will still be there for an admin to create an Consumer and take a look.

Purge or Truncate (not everything)

We offer purge but that deletes all messages from a Stream. Wondering of you may want to truncate. This is if no message or byte limits were set.

NAK w/ Duration Before Redelivery

Should we allow a time duration to be optionally sent with a NAK to say "do not attempt a redelivery for delta time"

MsgSet Immutable?

Streams are always hashed and each message is hashed with sequence number and timestamp. However we do allow the ability to securely delete messages. Should we also allow the creator of a Stream to specify the set is strictly immutable? I had this programmed before where each message hash included the hash from the previous message, making the whole set tamper proof.

DR/Mirror

We will add the ability to mirror a Stream from one cluster to the next. Just need to think this through.

Account Template to Auto-create msgSets.

As we start to directly instrument accounts with JetStream limits etc., should we also allow a subject space that is not directly assigned to a Stream but creates a template for the system to auto-create Streams. Question is, should we auto-delete them as well, like STAN does?

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