Overview

Teaching: 5 min
Exercises: 10 min

Questions

• How can we make job templates?

Objectives

• Don’t Repeat Yourself (DRY)

• Making reusable/flexible CI/CD jobs

Hidden (keys) Jobs

A fun feature about GitLab’s CI YAML is the ability to disable entire jobs simply by prefixing the job name with a period (.). Naively, we could just comment it out

#hidden job:
#  script:
#    - make

but it’s much easier to simply write

.hidden job:
  script:
    - make

Why is this fun? We should be able to combine it with some other nice features of GitLab’s CI YAML to build…

Job Templates

From the previous lesson, our .gitlab-ci.yml looks like

hello world:
  script:
   - echo "Hello World"

build_skim:
  image: rootproject/root-conda:6.18.04
  before_script:
   - COMPILER=$(root-config --cxx)
   - FLAGS=$(root-config --cflags --libs)
  script:
   - $COMPILER -g -O3 -Wall -Wextra -Wpedantic -o skim skim.cxx $FLAGS

build_skim_latest:
  image: rootproject/root-conda:latest
  before_script:
   - COMPILER=$(root-config --cxx)
   - FLAGS=$(root-config --cflags --libs)
  script:
   - $COMPILER -g -O3 -Wall -Wextra -Wpedantic -o skim skim.cxx $FLAGS
  allow_failure: yes

We’ve already started to repeat ourselves. How can we combine the two into a single job template called .build_template? Let’s refactor things a little bit.

Refactoring the code

Can you refactor the above code by adding a hidden job (named .build_template) containing parameters that build_skim and build_skim_latest have in common?

Solution

hello world:
  script:
   - echo "Hello World"

.build_template:
  before_script:
   - COMPILER=$(root-config --cxx)
   - FLAGS=$(root-config --cflags --libs)
  script:
   - $COMPILER -g -O3 -Wall -Wextra -Wpedantic -o skim skim.cxx $FLAGS

build_skim:
  image: rootproject/root-conda:6.18.04
  before_script:
   - COMPILER=$(root-config --cxx)
   - FLAGS=$(root-config --cflags --libs)
  script:
   - $COMPILER -g -O3 -Wall -Wextra -Wpedantic -o skim skim.cxx $FLAGS

build_skim_latest:
  image: rootproject/root-conda:latest
  before_script:
   - COMPILER=$(root-config --cxx)
   - FLAGS=$(root-config --cflags --libs)
  script:
   - $COMPILER -g -O3 -Wall -Wextra -Wpedantic -o skim skim.cxx $FLAGS
  allow_failure: yes

The idea behind not repeating yourself is to merge multiple (job) definitions together, usually a hidden job and a non-hidden job. This is done through a concept of inheritance. Interestingly enough, GitLab CI/CD also allows for :job:extends as an alternative to using YAML anchors. I tend to prefer this syntax as it appears to be “more readable and slightly more flexible” (according to GitLab - but I argue it’s simply just more readable and has identical functionality!!!).

.only-important:
  only:
    - master
    - stable
  tags:
    - production

.in-docker:
  tags:
    - docker
  image: alpine

rspec:
  extends:
    - .only-important
    - .in-docker
  script:
    - rake rspec

will become

rspec:
  only:
    - master
    - stable
  tags:
    - docker
  image: alpine
  script:
    - rake rspec

Note how .in-docker overrides :rspec:tags because it’s “closest in scope”.

Anchors Away?

If we use extends to remove duplicate code, what do we get?

Solution

hello world:
  script:
   - echo "Hello World"

.build_template:
  before_script:
   - COMPILER=$(root-config --cxx)
   - FLAGS=$(root-config --cflags --libs)
  script:
   - $COMPILER -g -O3 -Wall -Wextra -Wpedantic -o skim skim.cxx $FLAGS

build_skim:
  extends: .build_template
  image: rootproject/root-conda:6.18.04

build_skim_latest:
  extends: .build_template
  image: rootproject/root-conda:latest
  allow_failure: yes

Look how much cleaner you’ve made the code. You should now see that it’s pretty easy to start adding more build jobs for other images in a relatively clean way, as you’ve now abstracted the actual building from the definitions.

Key Points

• Hidden jobs can be used as templates with the extends parameter.

• Using job templates allows you to stay DRY!