GitLab Runner understanding

How does GitLab Runner works:

PURPOSE: All documents are provided on this Blog just for educational purposes only.  Please make sure that you run it in your test environment before to move on to production environment. 

Note: Thanks to Aurora Wang to clear the concept! 

GitLab is a web-based Git repository that provides free open and private repositories. In oterwords we can as a Version Management Tool.

GitLab Runner is an application that works with GitLab CI/CD to run jobs in a pipeline.

 

GitLab Runners participate in a distributed work-stealing algorithm. They continually poll a GitLab instance for jobs that match their tags, execute them, and communicate the progress and results back. 

concurrent = 4 is a global option, it won't cause you to have 4 parallel executions. And limit is a runner option on how many executions the runner is doing.

In other words, suppose that you have this config concurrent=4 and only one runner defined with limit = 1. The maximum amount of executions you will do is 1, because you have only one runner that can run only one subprocess at the same time.

But suppose that you have the same config (concurrent=4) but you have 10 different runners running with limit=1. What this means is that only 4 of those runners will run executions at the same time at any given time and, when they run, they can spawn only one subprocess.

Concurrent: Limits how many jobs can run concurrently. The maximum number is all defined runners. 0 does not mean unlimited. 

Limit: Limit how many jobs can be handled concurrently by this token. 0 (default) simply means don’t limit

limit=4 è (how many executions the same runner can have)

 

Example1 :

STEPS:

1.     Set the parameter as follow: Current setting is=>> concurrent=1.  The new setting is =>> concurrent=4 (globally allows 4)

1.      Create 4 runners 
2.      Edit the limit parameter in each runner  =>> limit=1

3.    It could run 4 different runners parallel at the same time.

 

Example2:

1.     concurrent=4 (globally allows 4)
2.   Create 4 runners
3.     Runner 1 è limit=3 (the same runner can run parallel 3 times)
4.     Runner 2 è limit=2 (the same runner can run parallel 2 times)
5.     Runner 3 è limit=1 (this runner can just run one time =>> no parallel)

6.   Runner 4 è limit=4 (the same runner can run parallel 4 times)

What this means is that only 4 of those runners will run executions at the same time. Because we allow globally 4 concurrent è [concurrent=4 (globally allows 4)].

 

Example3:

1.     concurrent=10 (globally allows 10)
2.     Create 4 runners
3.     Runner 1 è limit=3 (the same runner can run parallel 3 times)
4.     Runner 2 è limit=2 (the same runner can run parallel 2 times)
5.     Runner 3 è limit=1 (this runner can just run one time =>> no parallel)

6.    Runner 4 è limit=4 (the same runner can run parallel 4 times)

      What this means is that all 4 runners can have run 10 executions at the same time. Because we allow globally 10 concurrent è [concurrent=10 (globally allows 10)]. Each runner limit has different, but not much then 10.

If you want to make chane in your runner config. You need to do as follow:

vi /etc/gitlab-runner/config.toml

Change the concurrent and limit values. 

Restart runner 

gitlab-runner list
gitlab-runner verify
gitlab-runner stop
gitlab-runner restart
gitlab-runner status
gitlab-runner start

-- Follwoing command stop your complete gitlab envoronment.
gitlab-ctl status
gitlab-ctl stop

gitlab-ctl start

Hope this helps.

You can Create runner as follow:

You need registration token.

Go to on you GitLab Web Link:

Groups =>> Explore groups =>>{Choos a group}: Test-HowKnow =>> {on the left side}: Setting=>> CI/CD =>> Runners =>> Expand [you find there the registration tocken 

gitlab-runner register -n --url [GitLab Server URL]/ --limit 1 --registration-token [registrationtoken] --executor docker --description "Test Deployment" --docker-image "docker:latest" --docker-privileged --docker-volumes /var/run/docker.sock:/var/run/docker.sock