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Jenkins Inbound Agent with enhanced capabilities

This docker image is originally based on jenkins/inbound-agent and was replaced with the alpine image of odavid/jenkins-jnlp-slave in order to resolve the docker-in-docker requirement for more flexible CI agent deployments required to support docker and docker-compose calls in the qa environment.

To be able to use MQTT and to ease handling of json objects the mosquitto_clients and jq library are added.

Build

To build the image manually:

docker build --no-cache -t jforge/jenkins-inbound-agent .

Usage

Use the jenkins-inbound-agent command line options or use corresponding environment variables.

The privileged mode (--privileged) is required and either the -e DIND=true flag or the docker daemon socket mount (-v /var/run/docker.sock:/var/run/docker.sock).

For ease of use of docker inside jenkins build pipelines use the docker-in-docker feature by setting the flag DIND=true as an environment variable.

Refer to the jenkins master configuration for this agent node for the node label and ensure that configuration uses /home/jenkins/agent as the remote root folder.

Docker run

docker run --init --privileged \
  -e JENKINS_URL=https://jenkins.example.org \
  -e JENKINS_WEB_SOCKET=true \
  -e JENKINS_SECRET=TheAgentSecret  \
  -e JENKINS_AGENT_NAME=MyInboundAgent \
  -e DIND=true \
  -e TINI_SUBREAPER=true \
  jforge/jenkins-inbound-agent:latest

Docker-compose

See the compose folder for a ready to use compose file. Just create an .env file for it (or environment variables on the shell) specifying the 3 required environment variables.

The say docker-compose up -d on the target host acting as a build node.

This composition uses the webSockets connection only (instead of JNLP-4):

version: '3.7'
services:
  inbound-agent:
    image: jforge/jenkins-inbound-agent
    init: true
    privileged: true
    environment:
      - JENKINS_URL=${JENKINS_MASTER_URL}
      - JENKINS_SECRET=${JENKINS_AGENT_SECRET}
      - JENKINS_AGENT_NAME=${JENKINS_AGENT_NAME}
      - JENKINS_WEB_SOCKET=true
      - DIND=true
      - TINI_SUBREAPER=true

Using the image with a Jenkins Pipeline

To use the image with the added feature prepare the Jenkins node on the master and start the node as described above.

Zombie Reaping (removing orphaned processes)

In case of orphaned process the tini program is responsible for removing them and performing signal forwarding. It runs transparently as a single child process (on a container).

Orphan processes consume resources, affect the process identifier namespace they run in and make the environment unstable or unusable, so that they should be removed.

By default, Tini needs to run using the process identifier (PID) 1 to remove orphaned processes. If PID 1 cannot be used or if containers are run without PID namespace isolation, the Tini program should be registered as a process subreaper by setting the TINI_SUBREAPER environment variable to true. This ensures the orphaned processes to be re-parented as children of the Tini program which can then remove them to complete its execution.

References