Prepare a Jenkins Docker Build Node with Ansible

Recently I have started to take more time to learn Ansible, building role-based projects similar to what I’ve always done with Puppet, as opposed to simple monolithic playbooks. I still believe Puppet is superior to Ansible when a host has a long list of items to be managed, whereas Ansible excels for more narrowly-scoped tasks such as pushing some files out and restarting a service. However, I’m sure that most would disagree with me, and in my lab I have chosen to use Ansible for most tasks in keeping with the latest trend. For this case, I created a simple Ansible project to set up a CentOS/EL8 Jenkins build node running Docker. The directory structure of this project is below:

├── inventory
├── jenkins_build.yml
├── roles
    ├── docker
    │   └── tasks
    │       ├── install.yml
    │       ├── main.yml
    │       └── service.yml
    ├── jenkins_node
        ├── files
        │   └── jenkins.pub
        └── tasks
            ├── install.yml
            ├── main.yml
            └── user.yml

First, I created a simple inventory file. The inventory just has one host for now with no variables.

[jenkins_build]
jenkins-node2

I then created a simple playbook, jenkins_build.yml, that includes the two roles I need.

---
- hosts: jenkins_build
  roles:
    - docker
    - jenkins_node

Next, I created the roles with mkdir -p roles/docker/tasks and mkdir -p roles/jenkins_node/{tasks,files}. This project is extremely simple; it does not use templates, variables, handlers, etc. and probably could have just used a monolithic playbook for brevity’s sake. However, I decided to use the full directory structure so that the roles could be reused later.

First, I’ll go over the Docker role. All it does is install the docker-ce packages from Docker and ensures that the service is running. The install yml file also needs to install the Docker GPG key:

---
# install.yml
  - rpm_key: state=present key=https://download.docker.com/linux/centos/gpg

  - yum_repository:
      name: docker-ce-stable
      description: Docker CE Stable - $basearch
      baseurl: https://download.docker.com/linux/centos/$releasever/$basearch/stable
      gpgcheck: yes
      gpgkey: https://download.docker.com/linux/centos/gpg

  - yum: name=docker-ce state=installed
---
# service.yml
  - service: name=docker state=started enabled=yes

main.yml includes both of the above:

  - include: install.yml
  - include: service.yml

Next, the Jenkins node role: this role installs the required packages and creates the jenkins user. First, you will need a generate a password hash for the Jenkins user. To do so, execute the below Python one-liner:

python -c 'import crypt,getpass;pw=getpass.getpass();print(crypt.crypt(pw) if (pw==getpass.getpass("Confirm: ")) else exit())'

Then include the resulting hash in your user.yml file:

---
  - user:
      name: jenkins
      state: present
      password: 'hash'
      group: users
      groups:
        - docker

  - ansible.posix.authorized_key:
      user: jenkins
      key: "{{ lookup('file', 'jenkins.pub') }}"
      state: present

If you want your Jenkins server to connect to the node using an SSH key, you will need to place the public key in a file located in files. I created this file as jenkins.pub. Then create the .yml files that install the necessary packages and include the tasks.

# install.yml
---
  - yum:
      name:
        - git
        - java-1.8.0-openjdk
      state: installed
# main.yml
---
  - include: install.yml
  - include: user.yml

Finally, run the playbook against the Jenkins build node from a host with Ansible installed. You might want to run it first with the -C option to ensure that it does what you expect it to do:

ansible-playbook -Kkb -i inventory -D jenkins_build.yml

If this was successful, you should then be able to add the node to Jenkins, located at Dashboard > Manage Jenkins > Manage Nodes and Clouds > New Node:

Setting up a Jenkins build node. The Labels section is optional, but is a method of restricting on which node a job can be run.

This concludes my blog post. This is a rather simple Ansible task, but demonstrates a use case for it, especially if you are setting up a bunch of build nodes for Jenkins. In my next post I will show how I configured a Jenkins job to build an RPM in a Docker container on the node I added here.