Using testcontainers in a Jenkins Docker Agent: containers fail to start, NoRouteToHostException

After some experimentation, I've discovered the cause of the problem. The crucial action is trying to create a Docker bridge network (using docker network create, or a testcontainers Network object) inside a Docker container that is itself running in a Docker bridge network. If you do this you will not get an error message from Docker, nor will the Docker daemon log file include any useful messages. But attempts to use the network will result in there being "no route to host".

I fixed the problem by giving my outermost Docker containers (the Jenkins Agents) access to the host network, by having Jenkins provide a --network="host" option to its docker run command:

pipeline {    agent {        dockerfile {            filename 'Dockerfile.jenkinsAgent'            additionalBuildArgs  ...            args '-v /var/run/docker.sock:/var/run/docker.sock ... --network="host" -u jenkins:docker'       }    }    stages {...

That is OK because the Jenkins Agents do not need the level of isolation given by a bridge network.

In my case it was enough to add two arguments to Docker agent options:

• Docker socket as volume
• add --group-add parameter with ID of docker group

pipeline {    agent any    stages {        stage('Gradle build') {            agent {                docker {                    reuseNode true                    image 'openjdk:11.0-jdk-slim'                    args  '-v /var/run/docker.sock:/var/run/docker.sock --group-add 992'                }            }            steps {                sh 'env | sort'                sh './gradlew build --no-daemon --stacktrace'            }        }    } // stages} // pipeline