Buildkit does not run properly

Question

An image for the Jenkins agent buildkit was created using the Dockerfile below.

FROM jenkins/inbound-agent:alpine as jnlp

FROM moby/buildkit as buildkit

USER root

RUN apk update \
  && apk upgrade \
  && apk add --update openjdk11 tzdata curl unzip bash \
  && rm -rf /var/cache/apk/*

COPY --from=jnlp /usr/local/bin/jenkins-agent /usr/local/bin/jenkins-agent
COPY --from=jnlp /usr/share/jenkins/agent.jar /usr/share/jenkins/agent.jar

ENTRYPOINT ["/usr/local/bin/jenkins-agent"]

The image runs normally as a Kubernetes pod. However, when I try to build the image using buildkit in the pod, an error occurs. I don't know what the problem is.

+ buildctl build --frontend dockerfile.v0 --local 'context=.' --local 'dockerfile=.' --output 'type=image,name=docker.io/username/image'
error: listing workers for Build: failed to list workers: Unavailable: connection error: desc = "transport: error while dialing: dial unix /run/buildkit/buildkitd.sock: connect: no such file or directory"

When executing the above command, the following error occurs.

The buildkit was registered in the Jenkins helm chart as follows.

  builkit:
    podName: buildkit
    customJenkinsLabels: buildkit
    image: "agent-buildkit"
    tag: "1.0"
    alwaysPullImage: true

Answer 1

ENTRYPOINT in your dockerfile running jenkins-agent but do nothing with buildkit. You need to check what the ENTRYPOINT in the original moby/buildkit image and create a custom script that will do both:

1. Start buildkit daemon
2. Start jenkins-agent

It's not ideal when you have multiple processes in your docker image, so it would be nice to add child management to your script (catch signals with trap and gracefully shutdown both jenkins and buildkit).