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Maven / GitLab CI Basics Interview Questions

What is a GitLab Runner and what types are available?

A GitLab Runner is an agent (a program) that picks up CI/CD jobs from GitLab and executes them. Runners are separate from the GitLab server - they can run on any machine including physical servers, VMs, containers, or cloud instances.

Runner types by scope
TypeScopeConfigured at
Instance runners (shared)Available to all projects on a GitLab instanceAdmin area (self-managed) or GitLab.com
Group runnersAvailable to all projects in a group and its subgroupsGroup > Settings > CI/CD > Runners
Project runners (specific)Available to one specific projectProject > Settings > CI/CD > Runners

GitLab.com users: GitLab.com provides instance runners that you can use immediately without any setup. For self-managed GitLab, administrators must install and register runners separately.

Runner executors: how the runner actually runs jobs depends on its executor type:

Common runner executors
ExecutorRuns jobs inUse case
ShellDirect shell on the runner machineSimple setups; persistent environment
DockerA fresh Docker container per jobIsolated, reproducible environments
Docker+MachineAuto-scaled Docker VMsHigh concurrency, auto-scaling
KubernetesA Kubernetes pod per jobCloud-native, auto-scaling
Virtual MachineA VM snapshotFull VM isolation

You specify which runner to use by adding tags to a job. The runner must have the same tag registered to pick up that job.

What is the scope of a GitLab 'group runner'?
How do you direct a GitLab CI job to a specific runner?

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