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geard is a command line client for installing Docker images as containers onto a systemd-enabled Linux operating system (systemd 207 or newer). It may be run as a command:

$ sudo gear install openshift/busybox-http-app my-sample-service

to install the public image openshift/busybox-http-app to systemd on the local machine with the service name "ctr-my-sample-service". The command can also start as a daemon and serve API requests over HTTP (default port 43273) :

$ sudo gear daemon
2014/02/21 02:59:42 ports: searching block 41, 4000-4099
2014/02/21 02:59:42 Starting HTTP on :43273 ...


CLI can connect to this agent:
$ gear stop localhost/my-sample-service
$ gear install openshift/busybox-http-app localhost/my-sample-service.1 localhost/my-sample-service.2
$ gear start localhost/my-sample-service.1 localhost/my-sample-service.2

The geard agent exposes operations on containers needed for large scale orchestration in production environments, and tries to map those operations closely to the underlying concepts in Docker and systemd. It supports linking containers into logical groups (applications) across multiple hosts with iptables based local networking, shared environment files, and SSH access to containers. It is also a test bed for prototyping related container services that may eventually exist as Docker plugins, such as routing, event notification, and efficient idling and network activation.

The gear daemon and local commands must run as root to interface with the Docker daemon over its Unix socket and systemd over DBus.

What is a "gear", and why Docker?

In OpenShift Origin, a gear is a secure, isolated environment for user processes using cGroups and SELinux. As Linux namespace technology has evolved to provide other means of constraining processes, the term "container" has become prevalent, and is used interchangeably below. Docker has made the creation and distribution of container images effortless, and the ability to reproducibly run a Linux application in many environments is a key component for developers and administrators. At the same time, the systemd process manager has unified many important Linux process subsystems (logging, audit, managing and monitoring processes, and controlling cGroups) into a reliable and consistent whole.

What are the key requirements for production containers?

  • Containers are securely isolated from the host except through clear interfaces

By default, a container should only see what the host allows - being able to become root within a container is extremely valuable for installing packaged software, but that is also a significant security concern. Both user namespaces and SELinux are key components to protecting the host from arbitrary code, and should be secure by default within Docker. However, as necessary administrators should be able to expose system services or other containers to a container. Other limits include network abstractions and quota restrictions on the files containers create.

  • Container processes should be independent and resilient to failure

Processes fail, become corrupted, and die. Those failures should be isolated and recoverable - a key feature of systemd is its comprehensive ability to handle the wide variety of process death and restart, recover, limit, and track the involved processes. The failure of other components within the system should not block restarting or reinitializing other containers to the extent possible, especially in bulk.

  • Containers should be portable across hosts

A Docker image should be reusable across hosts. This means that the underlying Docker abstractions (links, port mappings, environment files) should be used to ensure the gear does not become dependent on the host system except where necessary. The system should make it easy to share environment and context between gears and move or recreate them among host systems.

  • Containers must be auditable, constrained, and reliably logged

Many of the most important characteristics of Linux security are difficult to enforce on arbitrary processes. systemd provides standard patterns for each of these and when properly integrated with Docker can give administrators in multi-tenant or restricted environments peace of mind.

Actions on a container

Here are the supported container actions on the agent - these should map cleanly to Docker, systemd, or a very simple combination of the two. Extensions are intended to simplify cross container actions (shared environment and links)

  • Create a new system unit file that runs a single docker image (install and start a container)

    $ gear install openshift/busybox-http-app localhost/my-sample-service --start -p 8080:0

    $ curl -X PUT "http://localhost:43273/container/my-sample-service" -H "Content-Type: application/json" -d '{"Image": "openshift/busybox-http-app", "Started":true, "Ports":[{"Internal":8080}]}'

  • Stop, start, and restart a container

    $ gear stop localhost/my-sample-service
    $ gear start localhost/my-sample-service
    $ gear restart localhost/my-sample-service

    $ curl -X PUT "http://localhost:43273/container/my-sample-service/stopped" $ curl -X PUT "http://localhost:43273/container/my-sample-service/started" $ curl -X POST "http://localhost:43273/container/my-sample-service/restart"

  • Deploy a set of containers on one or more systems, with links between them:

    # create a simple two container web app
    $ gear deploy deployment/fixtures/simple_deploy.json localhost

    Deploy creates links between the containers with iptables - use nsenter to join the container web-1 and try curling to connect to the second web container. These links are stable across hosts and can be changed without the container knowing.

    # create a mongo db replica set (some assembly required)
    $ gear deploy deployment/fixtures/mongo_deploy.json localhost
    $ sudo switchns --container=db-1 -- /bin/bash
    > mongo
    MongoDB shell version: 2.4.9
    > rs.initiate({_id: "replica0", version: 1, members:[{_id: 0, host:""}]})
    > rs.add("")
    > rs.add("")
    > rs.status()
    # wait....
    > rs.status()

    Note: The argument to initiate() sets the correct hostname for the first member, otherwise the other members cannot connect.

  • View the systemd status of a container

    $ gear status localhost/my-sample-service
    $ curl "http://localhost:43273/container/my-sample-service/status"
  • Tail the logs for a container (will end after 30 seconds)

    $ curl -H "Accept: text/plain;stream=true" "http://localhost:43273/container/my-sample-service/log"
  • List all installed containers (for one or more servers)

    $ gear list-units localhost
    $ curl "http://localhost:43273/containers"
  • Perform housekeeping cleanup on the geard directories

    $ gear clean
  • Create a new empty Git repository

    $ curl -X PUT "http://localhost:43273/repository/my-sample-repo"
  • Link containers with local loopback ports (for e.g. -> If local ip isn't specified, it defaults to

    $ gear link -n= localhost/my-sample-service
    $ curl -X PUT -H "Content-Type: application/json" "http://localhost:43273/container/my-sample-service" -d '{"Image": "openshift/busybox-http-app", "Started":true, "Ports":[{"Internal":8080}], "NetworkLinks": [{"FromHost": "","FromPort": 8081, "ToHost": "","ToPort": 8080}]}'
  • Set a public key as enabling SSH or Git SSH access to a container or repository (respectively)

    $ gear add-keys --key-file=[FILE] my-sample-service
    $ curl -X POST "http://localhost:43273/keys" -H "Content-Type: application/json" -d '{"Keys": [{"Type":"authorized_keys","Value":"ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEA6NF8iallvQVp22WDkTkyrtvp9eWW6A8YVr+kz4TjGYe7gHzIw+niNltGEFHzD8+v1I2YJ6oXevct1YeS0o9HZyN1Q9qgCgzUFtdOKLv6IedplqoPkcmF0aYet2PkEDo3MlTBckFXPITAMzF8dJSIFo9D8HfdOV0IAdx4O7PtixWKn5y2hMNG0zQPyUecp4pzC6kivAIhyfHilFR61RGL+GPXQ2MWZWFYbAGjyiYJnAmCP3NOTd0jMZEnDkbUvxhMmBYSdETk1rRgm+R4LOzFUGaHqHDLKLX+FIPKcF96hrucXzcWyLbIbEgE98OHlnVYCzRdK8jlqm8tehUc9c9WhQ=="}], "Containers": [{"Id": "my-sample-service"}]}'
  • Enable SSH access to join a container for a set of authorized keys

    # Make sure that /etc/ssh/sshd_config has the following two lines.
    AuthorizedKeysCommand /usr/sbin/gear-auth-keys-command
    AuthorizedKeysCommandUser nobody

    Restart sshd to pickup the changes.

    $ systemctl restart sshd.service

    Install and start a container in isolate mode which is necessary for SSH.

    $ gear install openshift/busybox-http-app testapp1 --isolate --start

    Add ssh keys.

    $ gear add-keys --key-file=/path/to/ testapp1

    ssh into the container.

    Note: All of this works with a remote host as well.

    $ ssh [email protected] 2014/05/01 12:48:21 docker: execution driver native-0.1 bash-4.2$ id uid=1019(container) gid=1019(container) groups=1019(container) bash-4.2$ ps -ef UID PID PPID C STIME TTY TIME CMD root 1 0 0 19:39 ? 00:00:00 su container -s /bin/bash -c /.container.cmd contain+ 16 1 0 19:39 ? 00:00:00 /usr/bin/ruby-mri /usr/mock/mock_server.rb /usr/mock /source/ contain+ 22 0 0 19:48 ? 00:00:00 /bin/bash -l contain+ 24 22 0 19:48 ? 00:00:00 ps -ef bash-4.2$

  • Build a new image using Source-to-Images (STI) from a source URL and base image

    # build an image on the local system and tag it as mybuild-1
    $ gear build git:// pmorie/fedora-mock mybuild-1

    remote build

    $ curl -X POST "http://localhost:43273/build-image" -H "Content-Type: application/json" -d '{"BaseImage":"pmorie/fedora-mock","Source":"git://","Tag":"mybuild-1"}'

  • Use Git repositories on the geard host

    # Create a repository on the host.
    # Note: We are using localhost for this example, however, it works for remote hosts as well.
    $ gear create-repo myrepo []

    Add keys to grant access to the repository.

    The write flag enables git push, otherwise only git clone i.e. read is allowed.

    $ gear add-keys --write=true --key-file=/path/to/ repo://myrepo

    Clone the repo.

    $ git clone [email protected]:~ myrepo

    Commit some changes locally.

    $ cd myrepo $ echo "Hello" > hi.txt $ git add hi.txt $ git commit -m "Add simple text file."

    Push the changes to the repository on the host.

    $ git push origin master

  • Fetch a Git archive zip for a repository

    $ curl "http://localhost:43273/repository/my-sample-repo/archive/master"
  • Set and retrieve environment files for sharing between containers (patch and pull operations)

    $ gear set-env localhost/my-sample-service A=B B=C
    $ gear env localhost/my-sample-service
    $ curl "http://localhost:43273/environment/my-sample-service"
    $ gear set-env localhost/my-sample-service --reset

    You can set environment during installation

    $ gear install ccoleman/envtest localhost/env-test1 --env-file=deployment/fixtures/simple.env

    Loading environment into a running container is dependent on the "docker run --env-file" option in Docker master from 0.9.x after April 1st. You must start the daemon with "gear daemon --has-env-file" in order to use the option - this option will be made the default after 0.9.1 lands and the minimal requirements will be updated.

  • More to come....

geard allows an administrator to easily ensure a given Docker container will always run on the system by creating a systemd unit describing a docker run command. It will execute the Docker container processes as children of the systemd unit, allowing auto restart of the container, customization of additional namespace options, the capture stdout and stderr to journald, and audit/seccomp integration to those child processes. Note that foreground execution is currently not in Docker master - see for some prototype work demonstrating the concept.

Each created systemd unit can be assigned a unique Unix user for quota and security purposes with the

flag, which prototypes isolation prior to user namespaces being part of Docker. An SELinux MCS category label will automatically be assigned to the container to separate it from the other containers on the system, and containers can be set into systemd slices with resource constraints.

Try it out

The geard code depends on:

  • systemd 207 (Fedora 20 or newer)
  • Docker 0.7 or newer (0.9.x from Apr 1 to use --env-file, various other experimental features not in tree)

If you don't have those, you can use the following to run in a development vm:

  • Vagrant
  • VirtualBox

If you have Go installed locally (have a valid GOPATH env variable set), run:

go get
cd $GOPATH/src/
vagrant up

If you don't have Go installed locally, run the following steps:

git clone [email protected]:openshift/geard && cd geard
vagrant up

vagrant up
will install a few RPMs the first time it is started. Once
vagrant up
is running, you can ssh into the vm:
vagrant ssh


script checks and downloads Go dependencies, builds the
binary, and then installs it to /vagrant/bin/gear and /usr/bin/gear. It has a few flags - '-s' builds with SELinux support for SSH and Git.
contrib/build -s

Once you've built the executables, you can run:

sudo $GOPATH/bin/gear daemon

to start the gear agent. The agent will listen on port 43273 by default and print logs to the console - hit CTRL+C to stop the agent.

See contrib/ and contrib/ for more examples of API calls.

An example systemd unit file for geard is included in the

directory. After building, the following commands will install the unit file and start the agent under systemd:
sudo systemctl enable $(pwd)/contrib/geard.service
sudo systemctl start geard.service

Report issues and contribute

Bugs are tracked by the Red Hat and OpenShift test teams in Bugzilla in the geard component, but you can always open a GitHub issue as well.

We are glad to accept pull requests for fixes, features, and experimentation. A rough map of the code structure is available here.

To submit a pull request, ensure your commit has a good description of the problem and contains a test case where possible for your function. We use Travis to perform builds and test pull requests - if your pull request fails Travis we'll try to help you get it fixed.

To run the test suite locally, from your development machine or VM, run:

$ contrib/test

to run just the unit tests. To run the full integration suite you should run:

$ contrib/build -g
$ contrib/test -a

which will build the current source, restart the gear daemon service under systemd, and then run both unit tests and integration tests. Be aware that at the current time a few of the integration tests fail occasionally due to race conditions - we hope to address that soon. Just retry! :)

How can geard be used in orchestration?

See the orchestrating geard doc

API Design

See the API design doc

Disk Structure

Description of storage on disk

geard Concepts

Outline of how some of the core operations work:

  • Linking - use iptable rules and environment variables to simplify container interconnect
  • SSH - generate authorized_keys for a user on demand
  • Isolated container - start an arbitrary image and force it to run as a given user on the host by chown the image prior to execution
  • Idling - use iptable rules to wake containers on SYN packets
  • Git - host Git repositories inside a running Docker container
  • Logs - stream journald log entries to clients
  • Builds - use transient systemd units to execute a build inside a container
  • Jobs - run one-off jobs as systemd transient units and extract their logs and output after completion

Not yet prototyped:

  • Integrated health check - mark containers as available once a pluggable/configurable health check passes
  • Joining - reconnect to an already running operation
  • Direct server to server image pulls - allow hosts to act as a distributed registry
  • Job callbacks - invoke a remote endpoint after an operation completes
  • Local routing - automatically distribute config for inbound and outbound proxying via HAProxy
  • Repair - cleanup and perform consistency checks on stored data (most operations assume some cleanup)
  • Capacity reporting - report capacity via API calls, allow precondition PUTs based on remaining capacity ("If-Match: capacity>=5"), allow capacity to be defined via config

Building Images

geard uses Source-to-Images (STI) to build deployable images from a base image and application source. STI supports a number of use cases for building deployable images, including:

  1. Use a git repository as a source
  2. Incremental builds: downloaded dependencies and generated artifacts are re-used across builds

A number of public STI base images exist:

  1. Ruby 1.9 on CentOS 6.x
  2. Wildfly 8 on CentOS 6.x
  3. WEBrick, a simple Ruby HTTP server, on latest Fedora

See the STI docs if you want to create your own STI base image.


Apache Software License (ASL) 2.0.

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