Jenkins Job Builder

Jenkins Job Builder is a system for configuring Jenkins jobs using simple YAML files stored in Git.

Overview

In order to make the process of managing thousands of Jenkins jobs easier, Jenkins Job Builder was designed to take YAML based configurations and convert those into jobs that are injected into Jenkins.

The documentation below describes how the OpenStack Infrastructure team uses the Jenkins Job Builder in our environment.

Configuring Projects

The YAML scripts to make this work are stored in the project-config: jenkins/jobs/ directory of the project-config repository. In this directory you can have four different types of yaml config files:

  • Jenkins Jobs Defaults in defaults.yaml.
  • Jenkins Jobs Macros to give larger config sections meaningful names in macros.yaml.
  • Project specific configurations in project_name.yaml.
  • Job template configurations. Need a projects.yaml file to specify how the templates should be filled out and templates go in template_name.yaml.

YAML Format

Defaults

Example defaults config:

- defaults:
    name: global
    project-type: freestyle
    concurrent: true

    wrappers:
      - timeout:
          timeout: 30
          fail: true
      - timestamps

    logrotate:
      daysToKeep: 1
      numToKeep: -1
      artifactDaysToKeep: -1
      artifactNumToKeep: -1

This config starts with the - defaults:: line. This specifies that this section contains default values rather than job specifications. In this section we specify a useful set of defaults including a default description indicating Puppet manages these jobs, jobs are allowed to run concurrently, and a thirty minute job timeout.

Macros

Macros exist to give meaningful names to blocks of configuration that can be used in job configs in place of the blocks they name. For example:

- builder:
    name: git-prep
    builders:
      - shell: "/slave_scripts/git-prep.sh"

- builder:
    name: docs
    builders:
      - shell: "/slave_scripts/run-docs.sh"

- publisher:
    name: console-log
    publishers:
      - scp:
          site: 'scp-server'
          files:
            - target: 'logs/$JOB_NAME/$BUILD_NUMBER'
              copy-console: true
              copy-after-failure: true

In this block of code we define two builder macros and one publisher macro. Each macro has a name and using that name in a job config is equivalent to having the yaml below the name in place of the name in the job config. The next section shows how you can use these macros.

Job Config

Example job config:

- job:
    name: example-docs
    node: node-label

    triggers:
      - zuul

    builders:
      - git-prep
      - docs

    publishers:
      - scp:
          site: 'scp-server'
          files:
            - target: 'dir/ectory'
              source: 'build/html/foo'
              keep-hierarchy: true
      - console-log

Each job specification begins with -job:. Under this section you can specify the job details like name, node, etc. Any detail defined in the defaults section that is not defined under this job will be included as well. In addition to attribute details you can also specify how jenkins should perform this job. What trigger methods should be used, the build steps, jenkins publishing steps and so on. The macros defined earlier make this easy and simple.

Job Templates

Job templates allow you to specify a job config once with arguments that are replaced with the values specified in projects.yaml. This allows you to reuse job configs across many projects. First you need a templated job config:

- job-template:
    name: '{name}-docs'

    triggers:
      - zuul

    builders:
      - git-prep
      - docs

    publishers:
      - scp:
          site: 'scp-server'
          files:
            - target: 'dir/ectory'
              source: 'build/html/foo'
              keep-hierarchy: true
      - console-log

    node: '{node}'


- job-group:
    name: python-jobs
    jobs:
      - '{name}-docs'

This takes the previous example-docs job and templatizes it. This will allow us to easily create example1-docs and example2-docs jobs. Each job template begins with - job-template: and the job specification is identical to the previous one, but we have introduced variable arguments. In this case {name} is a variable value that will be replaced. The values for name will be defined in the projects.yaml file.

The - job-group: section is not strictly necessary but allows you to group many job templates with the same variable arguments under one name.

The projects.yaml pulls all of the magic together. It specifies the arguments to and instantiates the job templates as real jobs. For example:

- project:
    name: example1
    node: bare-trusty

    jobs:
      - python-jobs

- project:
    name: example2
    node: bare-centos6

    jobs:
      - {name}-docs

Each project using templated jobs should have its own - project: section. Under this sections there should be a jobs: section with a list of job templates or job groups to be used by this project. Other values under the - project: section define the arguments to the templates lised under jobs:. In this case we are giving the docs template name and node values.

Notice that example1 makes use of the job group and example2 makes use of the job template.

Zuul

In our environment, we no longer use Jenkins to execute jobs. Zuul itself, via Ansible, runs the actual workload. Zuul reads JJB config files in order to define its jobs, so, aside from the detail of not actually using Jenkins or creating any jobs in it, the use of JJB to configure jobs in Zuul is the same.

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