How to make act utilize Docker BuildKit capabilities?

[GamePlayer-8]

Hello,

Whenever the Dockerfile within an action.yml file is containing COPY --chmod=755 [...], the run is failing.

I've tried enabling the docker buildkit by referring to this documentation, but didn't worked.

The error is as follows:

[Container 🔧/Build   ] ⭐ Run Set up job
[Container 🔧/Build   ] 🚀  Start image=alpine:3.23
[Container 🔧/Build   ]   🐳  docker pull image=alpine:3.23 platform= username= forcePull=true
[Container 🔧/Build   ]   🐳  docker create image=alpine:3.23 platform= entrypoint=["tail" "-f" "/dev/null"] cmd=[] network="host"
[Container 🔧/Build   ]   🐳  docker run image=alpine:3.23 platform= entrypoint=["tail" "-f" "/dev/null"] cmd=[] network="host"
[Container 🔧/Build   ]   🐳  docker exec cmd=[node --no-warnings -e console.log(process.execPath)] user= workdir=
[Container 🔧/Build   ]   ✅  Success - Set up job
[Container 🔧/Build   ]   ☁  git clone 'https://github.com/example/example' # ref=main
[Container 🔧/Build   ]   ☁  git clone 'https://github.com/example/example' # ref=main
[Container 🔧/Build   ] ⭐ Run Main Checkout
[Container 🔧/Build   ]   🐳  docker build -t act-example-example-main-dockeraction:latest /root/.cache/act/example-example@main
[Container 🔧/Build   ]   ❌  Failure - Main Checkout [5m48.451832006s]
[Container 🔧/Build   ] the --chmod option requires BuildKit. Refer to https://docs.docker.com/go/buildkit/ to learn how to build images with BuildKit enabled
[Container 🔧/Build   ] ⭐ Run Complete job
[Container 🔧/Build   ]   ✅  Success - Complete job
[Container 🔧/Build   ] 🏁  Job failed

Is there any way to make act utilize the buildkit?

[mg1986jp]

The issue is that act uses the legacy Docker builder (DOCKER_BUILDKIT=0 effectively) when it builds action images. The --chmod flag in COPY/ADD only works with BuildKit.

Try setting DOCKER_BUILDKIT=1 in your shell before running act:

export DOCKER_BUILDKIT=1
act

If that doesn't help (act might not pass that env through to its internal docker build calls), you could also try configuring Docker daemon-level BuildKit. Add this to your Docker daemon config (~/.docker/daemon.json or /etc/docker/daemon.json):

{
  "features": {
    "buildkit": true
  }
}

Then restart Docker and try again.

There's also a --use-new-action-cache flag in act that changes how it handles action building, though I'm not 100% sure it switches to BuildKit under the hood. Worth a shot if the above doesn't work.