Support --check mode in docker_stack plugin

[pyhedgehog]

SUMMARY

When running ansible-playbook --check I want to see:

1. If any service configuration should be changed/added/removed.
2. If any service deploy type attempts to change (and will fail).
3. if any configs will want's to redeploy (and will fail).
4. If any marked "external" network/config/secret don't exist.
5. If any service have placement constraints that can't be fulfilled by any node.
6. and so on.

ISSUE TYPE

• Feature Idea

COMPONENT NAME

community.docker.docker_stack

[felixfontein]

I think you are confusing check mode (-C) and diff mode (--diff). Diff mode shows (if supported by modules) differences, but doesn't stop the modules from applying changes. To do that, you need check mode.

[felixfontein]

@pyhedgehog can you please answer the question?

[pyhedgehog]

@felixfontein You are right. To add value I've listed most-wanted changes to be shown.

[felixfontein]

I think diff mode is also valuable, I was just confused because you mentioned diff mode, while your description seemed to claim that the module applies changes in check mode (which it should not, because as the module declares it does not support check mode, Ansible should automatically skip tasks using the docker_stack module).