`subdir not supported yet` while it should be supported

Behaviour

It is a simple repository with a Dockerfile (in a subdirectory). I want to build the image and push it to Docker Hub. It fails.

Steps to reproduce this issue

1. Fork https://github.com/jkulak/gh-actions-test
2. Commit any new file/change
3. Actions will run, and there will be an ERROR

Expected behaviour

It seems like a simple/basic use case for build-push-action. I would expect it build the Docker image and push it to Docker Hub.

Actual behaviour

Build fails. Seems like the action can not find the Dockerfile, which is located in the ./app directory of the repository.

#1 [internal] load git source https://github.com/***/gh-actions-test.git#7915aa22036b623876c4e04eeda5754b72aafaeb:app
#1 ERROR: subdir not supported yet

Configuration

• Repository URL (if public): https://github.com/jkulak/gh-actions-test
• Build URL (if public): https://github.com/jkulak/gh-actions-test/runs/7976332899?check_suite_focus=true

name: Docker Image CI

on:
    push:
        branches: ["*"]

jobs:
    docker:
        runs-on: ubuntu-latest
        steps:
            - name: Login to DockerHub
              uses: docker/login-action@v2
              with:
                  username: ${{ secrets.DOCKERHUB_USERNAME }}
                  password: ${{ secrets.DOCKERHUB_TOKEN }}
            - name: Build and push
              uses: docker/build-push-action@v3
              with:
                  context: "{{defaultContext}}:app"
                  push: true
                  tags: grabtrack/app:latest

Logs

logs_4.zip

Also:

1s
Run docker/build-push-action@v3
  with:
    context: {{defaultContext}}:app
    push: true
    tags: grabtrack/app:latest
    load: false
    no-cache: false
    pull: false
    github-token: ***
Docker info
Buildx version
  /usr/bin/docker buildx version
  github.com/docker/buildx 0.9.0+azure-[1](https://github.com/jkulak/gh-actions-test/runs/7976332899?check_suite_focus=true#step:3:1) 6113[2](https://github.com/jkulak/gh-actions-test/runs/7976332899?check_suite_focus=true#step:3:2)9fc7f1[3](https://github.com/jkulak/gh-actions-test/runs/7976332899?check_suite_focus=true#step:3:3)65556789bff[4](https://github.com/jkulak/gh-actions-test/runs/7976332899?check_suite_focus=true#step:3:4)747f608d40cdc8a9
/usr/bin/docker buildx build --iidfile /tmp/docker-build-push-0pxVKg/iidfile --secret id=GIT_AUTH_TOKEN,src=/tmp/docker-build-push-0pxVKg/tmp-1[5](https://github.com/jkulak/gh-actions-test/runs/7976332899?check_suite_focus=true#step:3:5)35-gtFtbXRZZaTx --tag grabtrack/app:latest --metadata-file /tmp/docker-build-push-0pxVKg/metadata-file --push https://github.com/***/gh-actions-test.git#7915aa2203[6](https://github.com/jkulak/gh-actions-test/runs/7976332899?check_suite_focus=true#step:3:6)b6238[7](https://github.com/jkulak/gh-actions-test/runs/7976332899?check_suite_focus=true#step:3:7)6c4e04eeda5754b72aafaeb:app
#1 [internal] load git source https://github.com/***/gh-actions-test.git#7915aa22036b623[8](https://github.com/jkulak/gh-actions-test/runs/7976332899?check_suite_focus=true#step:3:8)76c4e04eeda5754b72aafaeb:app
#1 ERROR: subdir not supported yet
------
 > [internal] load git source https://github.com/***/gh-actions-test.git#7[9](https://github.com/jkulak/gh-actions-test/runs/7976332899?check_suite_focus=true#step:3:9)15aa22036b623876c4e04eeda5754b72aafaeb:app:
------
ERROR: failed to solve: rpc error: code = Unknown desc = failed to solve with frontend dockerfile.v0: failed to read dockerfile: failed to load cache key: subdir not supported yet
Error: buildx failed with: ERROR: failed to solve: rpc error: code = Unknown desc = failed to solve with frontend dockerfile.v0: failed to read dockerfile: failed to load cache key: subdir not supported yet

[jkulak]

Thank you, it solves the issue.

The docs update makes it clear. 👍🏽

[polarathene]

It does not.

The docs update is very good at explaining it. But if you need extra clarification:

• buildx uses BuildKit, and docker (Docker Engine which provides docker migrated to the moby project since 2022. The moby README doesn’t mention it, but if you view their releases page, you can see that’s the case).
• docker releases provide their own buildx by default, but it’s version is too old to have the subdir support.
• buildx can be installed separately (which setup-buildx-action will do for you, and you have skipped this in your shared config, you need it as a step before build-push-action), doing so you can get a new enough version that has BuildKit version with the subdir feature support available.

---

Basically, docker does not yet have the compatibility. You’ll need to wait for a future release to be available.

However if you use setup-buildx-action prior to your build-push-action step, you’ll get a newer version of buildx that docker can use (via this actions docker-container builder, instead of the plain docker builder).

You don’t have to do anything else, just add the setup-buildx-action step, like this projects README shows.