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docker-jenkins-image

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Docker Jenkins Image

This is code for setting up a Jenkins into a docker container that can connect to the docker host daemon.

In order to enable access to the docker host daemon it is necessary to tell the container which is the id of the docker group in the host. We achieve this with the export of the enviroment variable DOCKER_GROUP_ID and declare it as an argument to the image build.

Dockerfile

Setting enviroment

We use always the latest oficial image of Jenkins of the DockerHub repository. At the moment of this code is written the latest image is 2.32.2

FROM jenkins:latest

Defining docker group id as an argument to the Dockerfile

ARG dockergroupid

We define root as the user to run the following instructions for setting the jenkins enviroment inside the container

    USER root 

    RUN mkdir /var/log/jenkins &&\
        mkdir /var/cache/jenkins 

    RUN chown -R jenkins:jenkins /var/log/jenkins &&\
        chown -R jenkins:jenkins /var/cache/jenkins

In case you want this folders to be reachable from the host just add this folders as volumes on the docker-compose.yml

Plugin configuration

In order to obtain a list of plugins installed on a running jenkins use: $ curl -sSL "http://user:password@jenkins_url[:port]/pluginManager/api/xml?depth=1&xpath=/*/*/shortName|/*/*/version&wrapper=plugins" | perl -pe 's/.*?<shortName>([\w-]+).*?<version>([^<]+)()(<\/\w+>)+/\1 \2\n/g'|sed 's/ /:/' > plugins.txt

If you don't need or don't want to preinstall any plugins just comment or delete following lines

   COPY plugins/install-plugins.sh install-plugins.sh
   COPY plugins/plugins.txt plugins.txt

Docker configuration

For Jenkins being able to run docker commands over the docker host it is not necessary to install a full docker on the container but add the bin/docker of the host as a volume. And (of course) set permissions. We don't enable all conections to the docker host but we add the Jenkins user of the container to the docker group in the host. It maintains somewhat security on our host.

We use the argument defined for adding the same docker group of the host to the container and add the Jenkins user to this group

  RUN echo "**** docker_group_id= $dockergroupid *****" &&\
      groupadd -g $dockergroupid docker
      
  RUN usermod -a -G docker jenkins

At the end we switch user on the container to jenkins

USER jenkins

docker-compose.yml

This file sets the running enviroment for Jenkins many of the configuration set here could be placed inside the Dockerfile, but we have chose to separate it.

We use last version of docker-compose yml definition but all the instructions here should be compatible at least with version 2 (I haven't try)

  version: '3'

We define just one service but I guess you can use this sames service inside any other docker-compose.yml with more services defined (such as nginx, there are many tutorials about setting nginx and Jenkins together)

This will tell the docker daemon that this service should be started whenever the daemon is started.

   ...
    restart: always

The build tag indicates Docker how to build the image in stead of using a ready to go image we will create this image in the "up" phase so the enviroment can be setted as specified in the Dockerfile.

    build:

Whenever the structure of the deployment is as shown in this project the context of the build is .

      context: .

As specified before, host docker group id should be an argument for the Dockerfile. For defining this parameter we must set as an enviroment variable (on the shell) the docker group id (DOCKER_GROUP_ID) we provide a small script that when run as

  $ . ./exp_docker_groupid.sh

over the same console we will run the docker-compose up will set up the variable and would be reachable during the image build

      args:
        dockergroupid: ${DOCKER_GROUP_ID}

I will define a name for the image in order to be able to push it to dockerHub. If you want to publish in your own repository you would want to change this line.

    image: gtunon/docker_master:beta

This container name is just to make it more traceable

    container_name: jenkins_master

The volumes: defined in this part of the service are part defined as main configuration

      - jenkins_home:/var/jenkins_home
      - /etc/localtime:/etc/localtime:ro

And particular for our Jenkins functioning. This volumes are just for sharing information with the host or other containers, you shoud configure your own volumes that satisfies your own needs.

      - /home/ubuntu/dockerImages:/home/ubuntu/dockerImages
      - built_jars:/home/ubuntu/shared/jars

The volumes necessary for using the docker of the host are:

     - /usr/bin/docker:/usr/bin/docker
     - /var/run/docker.sock:/var/run/docker.sock

We define the following ports as exposed on the host and maped to the container.

 ports:
      - "8081:8080"
      - "50000:50000"

The syntaxis is host_exposed_port:container_listening_port

Lastly we have the definition of the volumes defined by tags.

volumes:
  jenkins_home: {}
  built_jars: {}