Build cache for export step takes ~300s to complete

I followed the docs here to use caching in my actions, but my job takes an extremely long time (300s on average) to prepare and export build cache to GitHub. Is there a reason the caching takes so long?

YAML file:

build-api:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - uses: docker/setup-buildx-action@v1

      - name: Login to Github Packages
        uses: docker/login-action@v1
        with:
          registry: ghcr.io
          username: ${{ github.actor }}
          password: ${{ secrets.GITHUB_TOKEN }}

      - name: Build and push API
        uses: docker/build-push-action@v2
        with:
          context: .
          tags: |
            ghcr.io/<registry_name>/api:${{ github.event.release.tag_name }}
            ghcr.io/<registry_name>/api:latest
          build-args: |
            APP=api
          push: true
          cache-from: type=gha
          cache-to: type=gha,mode=max

[barthap]

Have similar issue, but this might be caused by cache size

Repro repo here, following jobs (clean runs, no previous cache):

• Example Server job run - actual build: 1min 20s, cache export: ~2min 30s (~90s preparing for export) - this is more or less acceptable dockerfile, ci workflow

• Example Web app job run - actual build: 5min, cache export: ~9 min (~8 min preparing for export) - the cache is useless here, it takes almost twice as long as actual clean build dockerfile, ci workflow

I’m using type=gha, mode=max, because all my Dockerfiles are multi-staged. In case of Web app, the reason is probably a huge yarn cache dir (~1.5 GB) which is copied between stages. An ideal solution would be to mount this as external volume, since this is actually used in other non-docker workflows too, with actions/cache@v2, but I have no idea if and how it is possible to share a directory between GHA and Dockerfile stages.

[BeyondEvil]

@barthap This was my thinking too (external volume mount), theoretically that shouldn’t be a problem or even difficult, but the question is how to turn off the cache export step.

ETA: We use self-hosted Github Actions runners.