Branch names with "/" fail when used in Docker tags

[toolmantim]

A common workflow of using cache-from is to include the branch name, via ${BUILDKITE_BRANCH}, in the Docker tag. But if someone pushes a branch with a / character in it (e.g. Dependabot's default behaviour), it will create an invalid tag and the push will fail.

For example:

steps:
  - plugins:
      - docker-compose#3.2.0:
          build: app
          cache-from:
            - app:index.docker.io/my-org/my-repo:${BUILDKITE_BRANCH}
            - app:index.docker.io/my-org/my-repo:master
          push:
            - app:index.docker.io/my-org/my-repo:${BUILDKITE_BRANCH}

[toolmantim]

There's no alternative pipeline.yml syntax for stripping or replacing the / in the environment interpolation, so our best bet is probably to do our own cleanup of the tag names, based on anything after the : character?

[tjwallace]

I created an agent hook for environment that sets BUILDKITE_BRANCH_SLUG:

#!/bin/bash
set -euo pipefail

echo '--- :house_with_garden: Setting BUILDKITE_BRANCH_SLUG'
export BUILDKITE_BRANCH_SLUG=$(echo $BUILDKITE_BRANCH | sed 's|/|--|g')

I then use that for my image tags

[bradleyess]

I'm doing the same as @tjwallace here :)

[TSMMark]

It seems like this is something that 99% of people using this plugin for caching would want to use... Should the readme be updated with an example?

[TSMMark]

No idea why but I had to move the export BUILDKITE_BRANCH_SLUG assignment out of .buildkite/hooks/environment and into .buildkite/hooks/post-checkout, otherwise the ecr cache was using :latest tag again

Enabling DOCKER_BUILDKIT also may not work well with caching in my experience.

[toothbrush]

The hack posted by @tjwallace got me unstuck. Is this (e.g., a Docker-tag-safe version of the Git branch name) something the buildkite-agent should always expose? I have these sorts of hacks (or another version, echo $BRANCH | tr '/' '-') littered throughout our codebases.

[toote]

I have created PR #345 to validate tags... unfortunately there is no way to correct them on the fly as the BUILDKITE_BRANCH variable is not supposed to be changed nor would we want to modify user-supplied configuration just like that.

What I've done instead is validate the values and just skip those (in cache-from and push options) that don't have valid tags. That way you can have a generic pipeline and those values that are valid will still work.