docker swarm does not respect depends_on

[vHanda]

Proposed changes

Swarmkit does not seem to have the concept of starting services in a particular order.

Tested with docker 1.13.1. Also, docker-compose bundle warns us about depends_on being unsupported.

It should be obvious from the documentation.

[mdlinville]

@aaronlehmann @nishanttotla PTAL

[aaronlehmann]

ping @dnephin

[dnephin]

The title of this issue is a bit misleading. I believe it should say "Document that docker stack deploy does not support depends_on"

I guess a note here wouldn't hurt.

There's some background in moby/moby#31333. The idea is that on swarm mode services are restarted until they are stable, so the order they are started shouldn't matter. There's also no way to say "has started" because service create is async.

[arvenil]

@dnephin

Definitely docs should state Note: These options are ignored when deploying a stack in swarm mode with a (version 3) Compose file.
Also docker stack deploy doesn't say anything that those options are ignored in contrast to raising warning for restart: always.

While it makes sense there is no such concept as deployment order with swarm, availability of those options in doc suggested I could use it to improve starting issues (e.g. some services die because other are not yet available so I get bunch containers that are restarted at initialization couple of times before they finally connect to each other).

Anyway, would be nice to update docs and maybe rise warning for ignored options as I lost plenty of time on this and on moby/moby#30404

[dnephin]

I've included this fix in #2278 because they are going to conflict.