How to run a specific job in gitlab CI

Question

We are facing a problem where we need to run one specific job in gitlab CI. We currently not know how to solve this problem. We have multitple jobs defined in our .gitlab-ci.yml but we only need to run a single job within our pipelines. How could we just run one job e.g. job1 or job2? We can't use tags or branches as a software switch in our environment.

.gitlab-ci.yml:

before_script:
  - docker info

job1:
  script:
    - do something

job2:
  script:
    - do something

Answer 1

You can use a gitlab variable expression with only/except like below and then pass the variable into the pipeline execution as needed.

This example defaults to running both jobs, but if passed 'true' for "firstJobOnly" it only runs the first job.

Old Approach -- (still valid as of gitlab 13.8) - only/except

variables:
  firstJobOnly: 'false'

before_script:
  - docker info

job1:
  script:
    - do something

job2:
  script:
    - do something
  except:
    variables:
      - $firstJobOnly =~ /true/i

Updated Approach - rules

While the above still works, the best way to accomplish this now would be using the rules syntax. A simple example similar to my original reply is below.

If you explore the options in the rules syntax, depending on the specific project constraints there are many ways this could be achieved.

variables:
  firstJobOnly: 'false'

job1:
  script: 
    - do something

job2:
  script: 
    - do something
  rules:
    - if: '$firstJobOnly == "true"'
      when: never
    - when: always