mqtt-launcher

mqtt-launcher is a Python program which subscribes to a set of MQTT topics and executes processes on the host it's running on. Launchable processes are configured on a per/wildcard basis, and they can be constrained to run only if a particular text payload is contained in the message.

For example, I can publish a message to my MQTT broker requesting mqtt-launcher create a particular semaphore file for me:

mosquitto_pub -t sys/file -m create

The configuration file must be valid Python and it is loaded once. It contains the topic / process associations.

# topic         payload value           program & arguments
"sys/file"  :   {
                    'create'        :   [ '/usr/bin/touch', '/tmp/file.one' ],
                    'false'         :   [ '/bin/rm', '-f', '/tmp/file.one'    ],
                    'info'          :   [ '/bin/ls', '-l', '/tmp/file.one' ],
                },

Above snippet instructs mqtt-launcher to:

• subscribe to the MQTT topic

  sys/file

• look up the payload string and launch the associated programs:
  • if the payload is

    create

    , then touch a file
  • if the payload is the string

    false

    , remove a file
  • if the payload is

    info

    , return information on the file

The payload value may be

None

@[email protected]

dev/2

dev/3

dev/4

mqtt-launcher publishes stdout and stderr of the launched program to the configured topic with

/report

sys/file/report

Screenshot

Here's the obligatory "screenshot".

Publishes                   Subscribes
-----------------------     ------------------------------------------------------------------
                        $ mosquitto_sub -v -t 'dev/#' -t 'sys/file/#' -t 'prog/#' 


mosquitto_pub -t prog/pwd -n
                        prog/pwd (null)
                        prog/pwd/report /private/tmp
mosquitto_pub -t sys/file -m create
                        sys/file create
                        sys/file/report (null)  # command has no output
mosquitto_pub -t sys/file -m info
                        sys/file info
                        sys/file/report -rw-r--r--  1 jpm  wheel  0 Jan 22 16:10 /tmp/file.one
mosquitto_pub -t sys/file -m remove
                        sys/file remove
                        # report not published: subcommand ('remove') doesn't exist
                        # log file says:
                        2014-01-22 16:11:30,393 No matching param (remove) for sys/file
mosquitto_pub -t dev/1 -m hi
                        dev/1 hi
                        dev/1/report total 16231
                        drwxrwxr-x+ 157 root  admin     5338 Jan 20 10:48 Applications
                        [email protected]   8 root  admin      272 Jan 25  2013 Developer
                        drwxr-xr-x+  72 root  wheel     2448 Oct 14 10:54 Library
                        ...
mosquitto_pub -t dev/2 -m 'Hi Jane!'
                        dev/2 Hi Jane!
                        dev/2/report 111 * Hi Jane! 222 Hi Jane! 333
mosquitto_pub -t dev/3 -m 'foo-bar'
                        dev/3 foo-bar
                        dev/3/report foo-bar
mosquitto_pub -t dev/4 -m 'foo/bar'
                        dev/4 foo/bar
                        dev/4/report var1=foo var2=bar

Configuration

mqtt-launcher loads a Python configuration from the path contained in the environment variable

$MQTTLAUNCHERCONFIG

launcher.conf

launcher.conf.example

Logging

mqtt-launcher logs its operation in the file configured as

logfile

Requirements

• Python
• paho-mqtt

Credits

This program was inspired by two related tools: * Peter van Dijk's mqtt-spawn * Dennis Schulte's mqtt-exec. (I'm not terribly comfortable running NodeJS programs, so I implemented the idea in Python.)