Creating a Docker container to run as a command

Aug 4, 2018

For the past two weeks at work I have been assigned to work on PHP projects. Though I used PHP some time ago - especially with Code Igniter and Laravel - I have not used it in a few years. And have been doing mostly Java nowadays.

The complete project setup was done by co-workers. I had a PHP project, using Symfony, several bundles and libraries, and Postgres. But it required just running a few commands to set up AWS settings, and then fire up Docker Compose.

Besides Docker Compose starting a web container, and another Postgres container, we used the web container to run Composer. In the past, I would see the PHP project mapped as a folder in the running container, and then composer would be executed in the host.

I noticed then that I could do the same to an image I created in 2016 to run Cylc. The previous version would be used to start a container in a terminal, then run some commands while maintaining the state within the container.

The new version now maps a volume to the version of cylc, installs the dependencies, and then allows the state to be maintained solely in the mapped volume.

Furthermore, the entrypoint of the image is the cylc command. Which means that you do not have to execute a terminal in order to run commands to the container (or change the command/entrypoint).

...
VOLUME "/opt/cylc" "/tmp" "/run" "/var/run" # we have the state stored only in /opt/cylc
WORKDIR "/opt/cylc"
ENV PATH /opt/cylc/bin:$PATH
WORKDIR /opt/cylc
ENTRYPOINT ["cylc"] # here's the trick!

It uses the same approach from the PHP image I am using for Composer, with a few additional improvements from the Best practices for writing Dockerfiles documentation.

$ docker run -ti -v "$(pwd -P)"/cylc:/opt/cylc cylc validate /opt/cylc/etc/examples/tutorial/oneoff/basic/
Valid for cylc-7.7.2
$ docker run -ti -v "$(pwd -P)"/cylc:/opt/cylc cylc register /opt/cylc/etc/examples/tutorial/oneoff/basic/
REGISTER /opt/cylc/etc/examples/tutorial/oneoff/basic/
$ docker run -ti -v "$(pwd -P)"/cylc:/opt/cylc cylc start --non-daemon --debug /opt/cylc/etc/examples/tutorial/oneoff/basic/
            ._.                                                       
            | |                 The Cylc Suite Engine [7.7.2]         
._____._. ._| |_____.           Copyright (C) 2008-2018 NIWA          
| .___| | | | | .___|  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
| !___| !_! | | !___.  This program comes with ABSOLUTELY NO WARRANTY;
!_____!___. |_!_____!  see `cylc warranty`.  It is free software, you 
      .___! |           are welcome to redistribute it under certain  
      !_____!                conditions; see `cylc conditions`.       
2018-07-30T12:10:32Z INFO - Suite starting: server=3714d1a17999:43040 pid=1
2018-07-30T12:10:32Z INFO - Cylc version: 7.7.2
2018-07-30T12:10:32Z INFO - Run mode: live
2018-07-30T12:10:32Z INFO - Initial point: 1
2018-07-30T12:10:32Z INFO - Final point: 1
2018-07-30T12:10:32Z INFO - Cold Start 1
2018-07-30T12:10:32Z DEBUG - [hello.1] -released to the task pool
2018-07-30T12:10:32Z DEBUG - BEGIN TASK PROCESSING
2018-07-30T12:10:32Z DEBUG - [hello.1] -waiting => queued
2018-07-30T12:10:32Z DEBUG - 1 task(s) de-queued
2018-07-30T12:10:32Z INFO - [hello.1] -submit-num=1, owner@host=localhost
2018-07-30T12:10:32Z DEBUG - [hello.1] -queued => ready
2018-07-30T12:10:32Z DEBUG - END TASK PROCESSING (took 0.00642895698547 seconds)
2018-07-30T12:10:32Z DEBUG - ['cylc', 'jobs-submit', '--debug', '--', '/opt/cylc/etc/examples/tutorial/oneoff/basic/log/job', '1/hello/01']
2018-07-30T12:10:33Z DEBUG - [client-connect] root@3714d1a17999:cylc-message privilege='full-control' 7b05596a-5971-4733-82de-28528f702ff0
2018-07-30T12:10:33Z INFO - [client-command] put_messages root@3714d1a17999:cylc-message 7b05596a-5971-4733-82de-28528f702ff0
2018-07-30T12:10:33Z DEBUG - [jobs-submit cmd] cylc jobs-submit --debug -- /opt/cylc/etc/examples/tutorial/oneoff/basic/log/job 1/hello/01
	[jobs-submit ret_code] 0
	[jobs-submit out]
	[TASK JOB SUMMARY]2018-07-30T12:10:32Z|1/hello/01|0|61
	[TASK JOB COMMAND]2018-07-30T12:10:32Z|1/hello/01|[STDOUT] 61
2018-07-30T12:10:33Z INFO - [hello.1] -(current:ready) submitted at 2018-07-30T12:10:32Z
2018-07-30T12:10:33Z INFO - [hello.1] -job[01] submitted to localhost:background[61]
2018-07-30T12:10:33Z DEBUG - [hello.1] -ready => submitted
2018-07-30T12:10:33Z INFO - [hello.1] -health check settings: submission timeout=None
2018-07-30T12:10:33Z DEBUG - BEGIN TASK PROCESSING
2018-07-30T12:10:33Z DEBUG - 0 task(s) de-queued
2018-07-30T12:10:33Z DEBUG - [hello.1] -forced spawning
2018-07-30T12:10:33Z DEBUG - END TASK PROCESSING (took 0.000992059707642 seconds)
2018-07-30T12:10:33Z INFO - [hello.1] -(current:submitted)> started at 2018-07-30T12:10:33Z
2018-07-30T12:10:33Z DEBUG - [hello.1] -submitted => running
2018-07-30T12:10:33Z INFO - [hello.1] -health check settings: execution timeout=None
2018-07-30T12:10:34Z DEBUG - BEGIN TASK PROCESSING
2018-07-30T12:10:34Z DEBUG - 0 task(s) de-queued
2018-07-30T12:10:34Z DEBUG - END TASK PROCESSING (took 0.000984191894531 seconds)
2018-07-30T12:10:43Z DEBUG - [client-connect] root@3714d1a17999:cylc-message privilege='full-control' 524d658e-9932-4135-9523-3c2ace3990cf
2018-07-30T12:10:43Z INFO - [client-command] put_messages root@3714d1a17999:cylc-message 524d658e-9932-4135-9523-3c2ace3990cf
2018-07-30T12:10:43Z INFO - [hello.1] -(current:running)> succeeded at 2018-07-30T12:10:43Z
2018-07-30T12:10:43Z DEBUG - [hello.1] -running => succeeded
2018-07-30T12:10:43Z INFO - Suite shutting down - AUTOMATIC
2018-07-30T12:10:44Z INFO - DONE
$

If you have a utility in your computer that requires a few dependencies, but that can store the state/data in a mapped volume, the same kind of container may be useful.

Categories: Blog

Tags: Cylc, Docker, Opensource, Workflows, Python