docker build with a dind self-hosted runner

[smaring]

A really basic workflow:

name: pr-to-dev
on: 
  pull_request:
    branches:
      - dev

jobs:
  build:
    runs-on: [self-hosted]

    steps:
      - uses: actions/checkout@v2
      - name: Build Docker image
        run: docker build . --file myDockerfile

There's nothing fancy in myDockerfile as its just for testing:

FROM alpine

RUN echo "hello world"

Since self-hosted in act asks for a Docker image to do the build I figured I probably need to use a dind image. It doesn't work though:

$ act pull_request -P self-hosted=docker:20.10.21-dind-alpine3.16
[pr-to-dev/build] 🚀  Start image=docker:20.10.21-dind-alpine3.16
[pr-to-dev/build]   🐳  docker pull image=docker:20.10.21-dind-alpine3.16 platform= username= forcePull=false
[pr-to-dev/build]   🐳  docker create image=docker:20.10.21-dind-alpine3.16 platform= entrypoint=["/usr/bin/tail" "-f" "/dev/null"] cmd=[]
[pr-to-dev/build]   🐳  docker run image=docker:20.10.21-dind-alpine3.16 platform= entrypoint=["/usr/bin/tail" "-f" "/dev/null"] cmd=[]
[pr-to-dev/build] ⭐ Run Main actions/checkout@v2
[pr-to-dev/build]   🐳  docker cp src=***** dst=*****
[pr-to-dev/build]   ✅  Success - Main actions/checkout@v2
[pr-to-dev/build] ⭐ Run Main Build Docker image
[pr-to-dev/build]   🐳  docker exec cmd=[bash --noprofile --norc -e -o pipefail /var/run/act/workflow/1] user= workdir=
| OCI runtime exec failed: exec failed: unable to start container process: exec: "bash": executable file not found in $PATH: unknown
[pr-to-dev/build]   ❌  Failure - Main Build Docker image
[pr-to-dev/build] exitcode '126': failure
[pr-to-dev/build] 🏁  Job failed
Error: Job 'build' failed

It says that it can't find bash inside the image, which appears to be a valid complaint:

$ docker run -i -t docker:20.10.21-dind-alpine3.16 /bin/bash
/usr/local/bin/docker-entrypoint.sh: exec: line 61: /bin/bash: not found

What you need is dind with bash. Somebody made one, although its a bit out-of-date now. Its easy enough to make your own, but this works:

$ act pull_request -P self-hosted=gdiener/dind-bash
[pr-to-dev/build] 🚀  Start image=gdiener/dind-bash
[pr-to-dev/build]   🐳  docker pull image=gdiener/dind-bash platform= username= forcePull=false
[pr-to-dev/build]   🐳  docker create image=gdiener/dind-bash platform= entrypoint=["/usr/bin/tail" "-f" "/dev/null"] cmd=[]
[pr-to-dev/build]   🐳  docker run image=gdiener/dind-bash platform= entrypoint=["/usr/bin/tail" "-f" "/dev/null"] cmd=[]
[pr-to-dev/build] ⭐ Run Main actions/checkout@v2
[pr-to-dev/build]   🐳  docker cp src=***** dst=*****
[pr-to-dev/build]   ✅  Success - Main actions/checkout@v2
[pr-to-dev/build] ⭐ Run Main Build Docker image
[pr-to-dev/build]   🐳  docker exec cmd=[bash --noprofile --norc -e -o pipefail /var/run/act/workflow/1] user= workdir=
Sending build context to Docker daemon  1.901MBkB
| Step 1/2 : FROM alpine
|  ---> 9c6f07244728
| Step 2/2 : RUN echo "hello world"
|  ---> Using cache
|  ---> 17590a4ffbe6
| Successfully built 17590a4ffbe6
[pr-to-dev/build]   ✅  Success - Main Build Docker image
[pr-to-dev/build] 🏁  Job succeeded

[hholst80]

You can define another shell in the workflow. I would recommend against using anything fancy in a direct workflow that depends on a particular shell. Use a repository script instead for that and keep programming logic outside the workflow file.