Pre-deploy image comparison misses mutable tag updates

[timidri]

Summary

doco-cd pre-deploy image change detection can miss updates when a compose service uses a mutable image tag such as :dev.

Example compose service:

image: ghcr.io/example/app:dev

A new image can be pushed to the same tag, but pre-deploy may still conclude that images have not changed.

Observed behavior

With force_image_pull: true, pre-deploy can log the equivalent of:

• force image pull enabled, checking for image updates
• images have not changed after pull
• no changes detected, skipping deployment

That is incorrect for floating tags if the pulled tag now points to a different image.

Likely cause

In internal/stages/stage_2_pre-deploy.go, pre-deploy compares image IDs before and after PullImages().

Those image IDs come from internal/docker/compose.go, where GetImages() uses compose project/container state rather than the configured compose image references themselves.

For floating tags:

• pulling ghcr.io/...:dev updates the local tag target
• existing running containers still point to the old image until recreate
• the before/after container-derived image IDs can remain identical
• pre-deploy therefore concludes that nothing changed

Expected behavior

Pre-deploy image update detection should use a signal that reflects the configured image references, not only the images currently attached to existing project containers.

Better long-term fix

For services with image: entries:

1. inspect the configured image refs before pull
2. pull
3. inspect the same refs after pull
4. compare digests, or image IDs as fallback

That would correctly detect floating-tag updates without depending on current container state.

Reproduction outline

1. Configure a stack with force_image_pull: true.
2. Use a mutable image tag like ghcr.io/example/app:dev in compose.
3. Push a new image to the same tag.
4. Trigger deployment.
5. Observe pre-deploy conclude that images did not change even though the tag now points to a new image.

[cduchenoy]

We are in the same situation: in development, we deploy an image whose tag is always dev.

With version v0.79, the deployment works correctly with the following configuration:

---
name: stack-name
working_dir: deploy
remove_orphans: true
compose_files:
  - docker-stack.yaml
force_image_pull: true
env_files:
  - deploy.env