Compose cannot recreate a container on Swarm if the container has an host port mapping

[jpetazzo]

What I have

• 5 nodes cluster
• Compose 1.6.0
• Swarm 1.1.0
• Engine 1.10.0

What I do

With the following docker-compose.yml:

www:
  image: nginx
  ports:
    - "8888:80"

I run:

docker-compose up -d
docker-compose up -d --force-recreate

What I expect to see

Container is created, then recreated.

What I see instead

Container is created, but when trying to recreate it, I see:

Recreating repro_www_1
ERROR: unable to find a node that satisfies container==a0e31139c706d24a739b88034e1f0b266eb049b6b304580c3b29bf4535d1c958

(Where a0e3... is the ID of the existing container.)

Cause

Compose provides a placement constraint to force the new container to be on the same host as the old one. But when there is a port mapping, this fails, even if the container has been stopped first, because Swarm doesn't deal with port mappings the same way as Engine does (a stopped container is still considered to use the port).

I attached the logs of docker inspect (before recreating the container) and the verbose output of docker-compose up -d.

inspect.log.txt
compose.log.txt

[dnephin]

We discussed this a bit, and the only solution we have right now is to not set the container== constraint if the container doesn't have volumes to copy over. That way at least we reduce the problem to "only containers that use both a host port and shared volumes", but I don't know of a way to fix it for everything.

[jpetazzo]

I have one use case where I need both placement constraint and port mapping: my load balancers are using volumes for dynamic reconfiguration.

Maybe Compose could do an indirection, i.e.:

• identify the node on which the container is running
• destroy the old container
• start the new container with affinity

(A similar plan is to create a dummy container to be used as an anchor for constraints; I think this is what was done in early Compose version to manage volumes.)

We might also want to punt this to Swarm to change the way host port mappings are handled but that might provoke other breakage on their end!

[aanand]

I find it a bit odd that Swarm considers a stopped container to be using the port. That pretty much breaks Compose's recreate logic, along with what seems like a generally reasonable use case outside of Compose (stop container A, start container A', remove container A).

[dnephin]

It is a bit unexpected at first, I added this note to the swarm docs a while ago to make it clear: https://docs.docker.com/swarm/scheduler/filter/#configure-the-available-filters:03285bdc704a53de2afbdd4c6c57e10d

I think it's necessary though (at least with the current architecture). If you check constraints when starting the container (instead of creating it), then you'd end up with a ton of race conditions where multiple containers get created on a node, then one starts and all those containers now refuse to start because the constraints aren't valid anymore (the started container stole the resources). It would also be an issue with restart policies.

[dnephin]

Maybe Compose could do an indirection

That might require compose to be a lot more aware of swarm.

It is possible that we could destroy the container before removing it. The problem with that approach is that if there is an error after we remove the original container, we completely lose track of the volumes that need to be applied to the new container (which is really bad).

True, we could also re-introduce the intermediate container that we used before rename existed. Copy the volumes onto the intermediate (which doesn't have the port binding), then onto the final container. I'd really like to avoid re-introducing the intermediate container.

What if you were to use named volumes instead of the unnamed container volumes? If we did #2866 (comment) and you were able to use named volumes, I think it might work.