Unexpected Dockerfile caching behaviour

[spearki]

Bug description

I think this is a known issue (within Gitpod at least), but it was a surprise to me that with a line in a .gitpod.Dockerfile like:

COPY the_file /here/

...changes to the_file don't actually trigger a rebuild of the image. We internally came up with the same workaround of using a dummy ENV var to break the cache manually and force a rebuild when any dependent files change.

It would be good to at least document this limitation, so devs don't have to independently discover it, usually following a period of frustration at why changes aren't being reflected in the workspace. 😞

Steps to reproduce

.gitpod.Dockerfile:

FROM gitpod/workspace-full:latest
COPY something /

Open a workspace in a repo with the above Dockerfile configured, then make a change to something, push and open a new workspace again. If a previously cached image exists, the image won't be rebuilt.

Workspace affected

No response

Expected behavior

In Docker/buildkit normally a change to a COPYied file will trigger a rebuild of that layer and following layers.

Example repository

No response

Anything else?

No response

[axonasif]

Hey @spearki

...changes to the_file don't actually trigger a rebuild of the image. We internally came up with the same workaround of using a dummy ENV var to break the cache manually and force a rebuild when any dependent files change.

This I think is how it was intended to be. You could also use #imagebuild:

• https://www.gitpod.io/docs/configure/workspaces/workspace-image#manually-rebuild-a-workspace-image

It would be good to at least document this limitation, so devs don't have to independently discover it, usually following a period of frustration at why changes aren't being reflected in the workspace. 😞

Valid point, added to the docs https://github.com/gitpod-io/website/pull/2866 🙏

[david-bakin]

Should also be rebuilt if FROM refers to an image which has changed in its repo (this happens when, e.g., the tag is :latest) (see this comment).

[spearki]

Valid point, added to the docs gitpod-io/website#2866 🙏

Thank you! Hopefully will help others avoid this pitfall in the future.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.