Add basic support for Swarm

[bfirsh]

You should be able to define a simple application with Fig and run it on Swarm with fig up -d.

This work was started in #763. One remaining issue is that Swarm returns names with more slashes in it than the normal Docker daemon, so Fig needs to parse this correctly.

Assumptions:

• links won't work
• volumes probably won't work

[dnephin]

Is this closed by #851 ?

[aanand]

Not quite - we need to ascertain exactly what does and doesn't work, verify that a satisfactory subset of functionality is supported, and document it.

[aanand]

So, once docker-archive/classicswarm#388 is merged, Swarm should have all the pieces in place for basic integration. Unfortunately, Compose doesn't, and the problem is volumes_from.

Swarm correctly co-schedules containers that use volumes_from to share volumes, but only if volumes_from is specified at creation time, whereas Compose specifies it at start time. This means that, with Compose as it currently works:

• recreate_container() is not guaranteed to place the new (or the intermediate) container on the right node.
• If it doesn't, starting the new container will fail.
• docker-compose up will therefore randomly fail on clusters of size > 1.

The "correct" solution is to specify volumes_from at creation time. There are two hiccups here:

• It may break backwards compatibility with Docker <1.4, unless the API allows you to specify it at both creation and start time. In any case don't think this is much of an issue, as we're pushing out a breaking version increment and Docker 1.4 is now two months old.
• docker-py doesn't let you pass volumes_from to create_container(), so we'll have to fix docker-py first.

A more hacky solution is to pass an affinity filter in when creating both the intermediate and the new container, i.e.

• Add an environment variable affinity:container==<id of old container> to the intermediate container
• Add an environment variable affinity:container==<id of intermediate container> to the new container

[aanand]

Regarding previous comment: see #972. I turned out to be wrong about docker-py - you can pass in a host_config as of API version 1.15.

[bfirsh]

https://github.com/docker/compose/blob/master/SWARM.md

[aanand]