Having Gitlab Projects calling the same gitlab-ci.yml stored in a central location - bash

Question

I have many Gitlab project followed the same CI template. Whenever there is a small change in the CI script, I have to manually modify the CI script in each project. Is there a way you can store your CI script in a central location and have your project called that CI script with some environment variable substitution? For instance,
gitlab-ci.yml in each project
/bin/bash -c "$(curl -fsSL <link_to_the_central_location>.sh)"
gitlab-ci.yml in the central location
stages:
- build
- test
build-code-job:
stage: build
script:
- echo "Check the ruby version, then build some Ruby project files:"
- ruby -v
- rake
test-code-job1:
stage: test
script:
- echo "If the files are built successfully, test some files with one command:"
- rake test1
test-code-job2:
stage: test
script:
- echo "If the files are built successfully, test other files with a different command:"
- rake test2

Answer 1

You do not need curl, actually gitlab supports this via the include directive.
you need a repository, where you store your general yml files. (you can choose if it is a whole ci file, or just parts. For this example lets call this repository CI and assume your gitlab runs at example.com - so the project url would be example.com/ci. we create two files in there just to show the possibilities.
is a whole CI definition, ready to use - lets call the file ci.yml. This approach is not really flexible
stages:
- build
- test
build-code-job:
stage: build
script:
- echo "Check the ruby version, then build some Ruby project files:"
- ruby -v
- rake
test-code-job1:
stage: test
script:
- echo "If the files are built successfully, test some files with one command:"
- rake test1
test-code-job2:
stage: test
script:
- echo "If the files are built successfully, test other files with a different command:"
- rake test2
is a partly CI definition, which is more extendable. lets call the files includes.yml
.build:
stage: build
script:
- echo "Check the ruby version, then build some Ruby project files:"
- ruby -v
- rake
.test:
stage: test
script:
- echo "this script tag will be overwritten"
There is even the option to use template string from yaml. please reference the gitlab documentation but it is similar to 2.
we do have our project which wants to use such definitions. so either
For the whole CI file
include:
- project: 'ci'
ref: master # think about tagging if you need it
file: 'ci.yml'
as you can see now we are referencing one yml file, with all the cahnges.
with partial extends
include:
- project: 'ci'
ref: master # think about tagging if you need it
file: 'includes.yml'
stages:
- build
- test
build-code-job:
extends: .build
job1:
extends: .test
script:
- rake test1
job2:
extends: .test
script:
- rake test2
As you see, you can easily use the includes, to have a way more granular setup. Additionally you could define at job1 and job2 variables, eg for the test target, and move the script block into the includes.yml
Futhermore you can also use anchors for the script parts. Which looks like this
includes.yml
.build-scirpt: &build
- echo "Check the ruby version, then build some Ruby project files:"
- ruby -v
- rake
.build:
stage: build
script:
- *build
and you can use also the script anchor within your configuration
For a deeper explanation you can also take a look at https://docs.gitlab.com/ee/ci/yaml/includes.html