Run Jenkins in Docker image and use host Docker process

This article demonstrates how to run Jenkins inside a Docker container while giving it access to the host machine’s Docker daemon.

FROM --platform=$BUILDPLATFORM jenkins/jenkins:2.426.1-lts-jdk17

USER root

RUN apt-get update && apt-get install -y lsb-release
RUN curl -fsSLo /usr/share/keyrings/docker-archive-keyring.asc 
  https://download.docker.com/linux/debian/gpg
RUN echo "deb [arch=$(dpkg --print-architecture)   signed-by=/usr/share/keyrings/docker-archive-keyring.asc]   https://download.docker.com/linux/debian   $(lsb_release -cs) stable" > /etc/apt/sources.list.d/docker.list
RUN apt-get update && apt-get install -y docker-ce-cli

RUN groupadd docker
RUN usermod -aG docker jenkins
RUN newgrp docker

RUN docker buildx create --name multibuilder --use

USER jenkins

# RUN jenkins-plugin-cli --plugins "blueocean:1.27.9 docker-workflow:1.29"

You can build the image with the following command:

docker build . --tag myregistry/jenkins:latest

To use the host Docker daemon within the Jenkins container, you will need to bind-mount the Docker socket from the host machine to the Jenkins container.

version: '3.8'
services:
  jenkins:
    container_name: jenkins
    image: myregistry/jenkins:latest
    volumes:
      - jenkins_home:/var/jenkins_home
      - /var/run/docker.sock:/var/run/docker.sock
      - /usr/bin/docker:/usr/bin/docker
    environment:
      - JAVA_OPTS=-Dhudson.footerURL=https://jenkins.example.com
    networks:
      - default_net
    ports:
      - 8080:8080
    deploy:
      replicas: 1
      restart_policy:
        condition: on-failure
    healthcheck:
      test: ['CMD-SHELL', 'sh', '-c', 'curl -v https://jenkins.example.com/login || exit 1']
      interval: 1m
      timeout: 10s
      retries: 3
      start_period: 60s

On the host machine, set the required permissions for docker.sock:

sudo chmod 666 /var/run/docker.sock

Security warning: Changing permissions on docker.sock grants Docker access to any user on the host. In production, use a more restrictive approach such as adding the Jenkins container user to the docker group, or use Docker socket proxies like Tecnativa/docker-socket-proxy.

Conclusion

With this setup, the Jenkins container can execute Docker commands on the host machine’s Docker daemon.