dockerized jenkins tutorial

Usage

docker-compose -p jenkins build
docker-compose -p jenkins up -d

Accessible by entering localhost on port 80.

Docker

image

• pull:

  • docker pull jenkins/jenkins

• build:

  • based on a Dockerfile
    • docker build -t myjenkins .

container

• run (create from an image):

  • with ports & name: -p outside_port:container_port --name=container-name
    • docker run -p 8080:8080 --name=jenkins-master jenkins/jenkins
      • note: if you're running docker network with nginx proxy listening on 80, you don't need jenkins to expose 8080 and can access jenkins by localhost:80
  • in daemon mode: -d
    • docker run -p 8080:8080 --name=jenkins-master -d jenkins/jenkins
  • with environment variables: --env VARIABLE="value"
    • give 8GB to JVM
      • docker run -p 8080:8080 --name=jenkins-master -d --env JAVA_OPTS="-Xmx8192m" jenkins/jenkins
    • add port 50000 for JNLP protocol (master-slave communication)
      • docker run -p 8080:8080 -p 50000:50000 --name=jenkins-master -d --env JAVA_OPTS="-Xmx8192m" jenkins/jenkins
        • more options: wiki.jenkins.io
  • with network attached: --network jenkins-net
    • docker run -p 8080:8080 -p 50000:50000 --name=jenkins-master --network jenkins-net --mount source=jenkins-log,target=/var/log/jenkins --mount source=jenkins-data,target=/var/jenkins_home -d myjenkins

• execute command in a running container:

  • docker exec jenkins-master ps -ef | grep java
  • docker exec jenkins-master tail -f /var/log/jenkins/jenkins.log
  • docker exec jenkins-master cat /var/jenkins_home/secrets/initialAdminPassword

• copy files from (not necessarily running) container:

  • docker cp jenkins-master:/var/log/jenkins/jenkins.log ./jenkins.log

• start (existing container):

  • docker start jenkins-master

• stop:

  • default:
    • standard stop process CTRL + c
  • daemonized:
    • docker stop jenkins-master

• remove:

  • docker rm jenkins-master

volume

• containers are disposable, volumes are permanent across disposes

• create:

  • docker volume create jenkins-log

• delete:

  • docker volume rm jenkins-data
  • docker volume prune

• mount:

  • docker run -p 8080:8080 -p 50000:50000 --name=jenkins-master --mount source=jenkins-log,target=/var/log/jenkins --mount source=jenkins-data,target=/var/jenkins_home -d myjenkins
    • when container which provided the data for volume is lost and you want to pull data out of the volume, you need to mount the volume to (any) container and then use docker cp.
    • if a volume doesn't exist, docker will create one based on the name given

network

• docker can create a DNS name on the network that match the container name. If you create a container named jenkins-master, docker can create http://jenkins-master:8080 for you. It's called "automatic service discovery".

• create

  • docker network create --driver bridge jenkins-net

• remove

  • docker network rm jenkins-net

compose

• docker-compose names containers in the following manner: [project]_[service]_[instance]. This should be considered, for example, in our jenkins.conf nginx configuration(proxy pass)
• docker-compose has several API versions, the latest one being 3 atm.
• if you don't define a network, docker-compose will create one for you.
  • similarly, if any of defined volumes doesn't exist, docker-compose will create them
• docker-compose.yml structure:

version: '3'  # docker-compose API version
volumes:  # docker volumes that should be made available
  jenkins-data:
  jenkins-log:
services:  # section used to define container startup
  master:  # service image corresponding to the `jenkins-master` container
    build: ./jenkins-master  # contains a relative path to a Dockerfile defining jenkins-master image
    ports:  # port mappings
      - "50000:50000"
    volumes:  # equivalent of `--mount` attribute
      - jenkins-log:/var/log/jenkins
      - jenkins-data:/var/jenkins_home
    networks:  # contains a network name the container will be using
      - jenkins-net

• build

  • docker-compose -p jenkins build
    • -p - project name, in this case it's jenkins. It will be a prefix for all resources created with docker-compose.yml. If you don't provide this, a name will be derived from the folder docker-compose.yml is in

• spin things up

  • docker-compose -p jenkins up -d
    • -d - run as a daemon

• see what's up

  • docker-compose -p jenkins ps
    • ps list of application containers

• put things down

  • docker compose -p jenkins down
    • -v add this option at the end if you want volumes deleted too

crawling for images

• use hub.dockerhub.com to search for available tags (and corresponding Dockerfiles) and to find out what other images the image depends on

nginx

nginx.conf file

• must have settings:
  • daemon off; - by default nginx starts as a daemon and returns exit 0. This makes Docker think that the process has stopped and the container can be stopped. We don't want this to happen.
  • proxy_set_header X-Real-IP $remote_addr;
  • proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; - so Jenkins can interpret requests properly. This eliminates warnings about improperly set headers.

jenkins.conf file

• must have settings:
  • proxy_pass http://jenkins-master:8080; - this expects a domain name of jenkins-master to exist (docker networks)

spinning up

• run nginx container on port 80 attached to jenkins-net
  • docker run -p 80:80 --name=jenkins-nginx --network jenkins-net -d myjenkinsnginx

files in jenkins-master

This repository contains the following content from jenkinsci docker repository

• ./install.plugins.sh
• ./jenkins-support
• ./plugins.sh

jenkins-slave

files/resolv.conf

• applied in case containers struggle to route or resolve DNS names correctly
• uses google DNS servers by default.

troubleshooting

Failure in name resolution (no internet in container)

• Add dns resolver to your docker config (/etc/docker/daemon.json)
  • This file might not exist. If that's the case, just create it.

{
  "dns": ["8.8.8.8"]
}

• Restart docker daemon

sudo service docker restart