Stack deploy vs service update, compose-like update

[Vanuan]

Description

For the blue-green deployment I need to change labels of my services whenever I switch from blue to green. So I went ahead and created two compose files: production-labels.yml and preparing-labels.yml. There's also "base" deploy file: deploy-base.yml.

The idea is that as I switch blue stack from "preparing" to "production" and green stack from "production" to "preparing", services in these two stack are not restarted. I checked it with docker service update --label-rm preparing --label-add production=true, services are fine.

The problem I'm facing is that it doesn't seem possible to do the same with docker deploy -c command. For example, if I change anything in deploy-base.yml, e.g. change image tag, when I'm doing the switch I can't preserve old image tags when applying new labels.

So here I am, asking for a feature to be able to do incremental stack deploy. That is, if I provide a compose file, only options that are present in this file are applied to current deployment.

Alternatively, I would be fine with a feature that can "dump" current stack into a generated compose file.

[Vanuan]

For the "dump current stack" there's a feature in swarmpit:
https://github.com/swarmpit/swarmpit/blob/1.5/src/clj/swarmpit/docker/engine/mapper/compose.clj

Unfortunately, it's written in Clojure, so can't be reused in docker. But I think it's a reasonable feature to do "partial" docker stack deploy. For example, there's --prune flag that removes services not included in current compose file. Maybe there's (would be) a similar --override flag which doesn't touch options not included in compose file.

The execution would be similar to:

docker stack dump --compose stack.yml
docker stack deploy -c stack.yml -c production-overrides.yml

For array and map options there's also functionality needed to specify whether override or extend options. As I understand there's only "extend" currently.

[Vanuan]

Alternatively, we can generate service update commands out of production-overrides.yml