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https://github.com/lelit/docker-compose-config-ordering-issue-demo

Demonstrate issue with list ordering in docker-compose 1.5.0
https://github.com/lelit/docker-compose-config-ordering-issue-demo

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Demonstrate issue with list ordering in docker-compose 1.5.0

Host: GitHub
URL: https://github.com/lelit/docker-compose-config-ordering-issue-demo
Owner: lelit
Created: 2015-11-07T13:36:06.000Z (about 9 years ago)
Default Branch: master
Last Pushed: 2015-11-07T13:54:16.000Z (about 9 years ago)
Last Synced: 2024-11-18T03:41:07.107Z (about 1 month ago)
Language: Python
Size: 0 Bytes
Stars: 1
Watchers: 3
Forks: 0
Open Issues: 0
Metadata Files:
- Readme: README.rst

Awesome Lists containing this project

README

        ===============================================================================

 Demonstrate issue with list ordering in docker-compose 1.5.0 (`issue 2342`__)

===============================================================================

This is a s{a/i}ample project that demonstrate an issue with the way docker-compose

configuration is loaded and interpolated.

It seems the new functionality is perturbed by the `hash randomization`__ feature introduced in

Python 3.3 (backported to Python 2.7, off by default).

__ https://github.com/docker/compose/issues/2342

__ https://docs.python.org/3/using/cmdline.html#envvar-PYTHONHASHSEED

Why it matters

==============

I'm using doit__ to automate some tasks. In particular I use its ability__ to keep an hash of

some configuration settings to *optimize* the build step, that is, to perform the build only

when needed because some setting has been changed.

__ http://pydoit.org/

__ http://pydoit.org/uptodate.html?highlight=config_changed#config-changed

As soon I switched one of my projects to Python 3, I quickly found that something wasn't

working as expected: the build task was invoking needless recompilation, but even

``docker-compose up`` kept recreating some of the services, even if their configuration didn't

change at all.

At first I thought that tweaking the `config_changed()`__ function to use ``pprint.pformat()``

instead of a plain ``repr()`` would be enough\ [*]_, but after some further investigation I found

that not only the ordering of *keys* in a dictionary was changing from one run to the next, but

also the ordering of *items* in various lists (``volumes``, to mention one).

__ https://github.com/pydoit/doit/blob/fc97427bb5e912b6544e91a4049e14aa2b5570a3/doit/tools.py#L62

.. [*] See https://github.com/pydoit/doit/issues/113

Demonstration

=============

This tiny example, adapted from the `getting started`__ chapter of the documentation, exhibits

the problem: the configuration of the ``web`` service defines two ``volumes``, in alphabetical

order, but when ``docker-compose`` reads it, that order is not (always) respected::

    $ tox

    py27 installed: docker-compose==1.5.0,docker-py==1.5.0,…

    py27 runtests: PYTHONHASHSEED='948517400'

    py27 runtests: commands[0] | ….tox/py27/bin/python …test.py

    {'ports': ['5000:5000'], 'volumes': ['…app:/srv/app', '…www:/srv/www'], 'build': '/tmp/testdc'}

    py34 installed: docker-compose==1.5.0,docker-py==1.5.0,…

    py34 runtests: PYTHONHASHSEED='948517400'

    py34 runtests: commands[0] | ….tox/py34/bin/python …test.py

    {'build': '/tmp/testdc', 'volumes': ['…app:/srv/app', '…www:/srv/www'], 'ports': ['5000:5000']}

    _______________ summary _______________

      py27: commands succeeded

      py34: commands succeeded

      congratulations :)

    $ tox

    py27 installed: docker-compose==1.5.0,docker-py==1.5.0,…

    py27 runtests: PYTHONHASHSEED='420369442'

    py27 runtests: commands[0] | ….tox/py27/bin/python …test.py

    {'ports': ['5000:5000'], 'volumes': ['…app:/srv/app', '…www:/srv/www'], 'build': '/tmp/testdc'}

    py34 installed: docker-compose==1.5.0,docker-py==1.5.0,…

    py34 runtests: PYTHONHASHSEED='420369442'

    py34 runtests: commands[0] | ….tox/py34/bin/python …test.py

    {'ports': ['5000:5000'], 'volumes': ['…app:/srv/app', '…www:/srv/www'], 'build': '/tmp/testdc'}

    _______________ summary _______________

      py27: commands succeeded

      py34: commands succeeded

      congratulations :)

    $ tox

    py27 installed: docker-compose==1.5.0,docker-py==1.5.0,…

    py27 runtests: PYTHONHASHSEED='774086394'

    py27 runtests: commands[0] | ….tox/py27/bin/python …test.py

    {'build': '/tmp/testdc', 'volumes': ['…www:/srv/www', '…app:/srv/app'], 'ports': ['5000:5000']}

    Traceback (most recent call last):

      File "…test.py", line 34, in 

        main()

      File "…test.py", line 31, in main

        assert volumes == sorted(volumes)

    AssertionError

    ERROR: InvocationError: '….tox/py27/bin/python …test.py'

    py34 installed: docker-compose==1.5.0,docker-py==1.5.0,…

    py34 runtests: PYTHONHASHSEED='774086394'

    py34 runtests: commands[0] | ….tox/py34/bin/python …test.py

    {'ports': ['5000:5000'], 'build': '/tmp/testdc', 'volumes': ['…app:/srv/app', '…www:/srv/www']}

    _______________ summary _______________

    ERROR:   py27: commands failed

      py34: commands succeeded

    $ tox

    py27 installed: docker-compose==1.5.0,docker-py==1.5.0,…

    py27 runtests: PYTHONHASHSEED='2212156821'

    py27 runtests: commands[0] | ….tox/py27/bin/python …test.py

    {'ports': ['5000:5000'], 'volumes': ['…www:/srv/www', '…app:/srv/app'], 'build': '/tmp/testdc'}

    Traceback (most recent call last):

      File "…test.py", line 34, in 

        main()

      File "…test.py", line 31, in main

        assert volumes == sorted(volumes)

    AssertionError

    ERROR: InvocationError: '….tox/py27/bin/python …test.py'

    py34 installed: docker-compose==1.5.0,docker-py==1.5.0,…

    py34 runtests: PYTHONHASHSEED='2212156821'

    py34 runtests: commands[0] | ….tox/py34/bin/python …test.py

    {'build': '/tmp/testdc', 'volumes': ['…www:/srv/www', '…app:/srv/app'], 'ports': ['5000:5000']}

    Traceback (most recent call last):

      File "…test.py", line 34, in 

        main()

      File "…test.py", line 31, in main

        assert volumes == sorted(volumes)

    AssertionError

    ERROR: InvocationError: '….tox/py34/bin/python …test.py'

    _______________ summary _______________

    ERROR:   py27: commands failed

    ERROR:   py34: commands failed

__ http://docs.docker.com/compose/gettingstarted/

Conclusion

==========

While I understand that from the operational point of view this may be a non-issue (that is,

everything works, even if sub optimally), it's a bit surprising that the ordering of list items

changes between runs. It may have bad effects when for some reason the order is important (I

cannot imagine a use case right now, but maybe a future setting may relay on a particular

order...)