What is the 'workflow' keyword in GitLab CI and how does it control pipeline creation?

The workflow keyword controls whether an entire pipeline is created at all, based on conditions. While rules on individual jobs control whether a specific job runs, workflow: rules controls whether the entire pipeline is created for a given event.

# Only create pipelines for main branch, MRs, and tags
workflow:
  rules:
    - if: $CI_COMMIT_BRANCH == "main"
    - if: $CI_PIPELINE_SOURCE == "merge_request_event"
    - if: $CI_COMMIT_TAG
    - when: never   # suppress all other pipeline triggers

# Name the pipeline dynamically
workflow:
  name: "Pipeline for $CI_COMMIT_REF_NAME"
  rules:
    - if: $CI_PIPELINE_SOURCE == "merge_request_event"
      name: "MR Pipeline: $CI_MERGE_REQUEST_TITLE"
    - if: $CI_COMMIT_BRANCH

# Prevent duplicate pipelines (MR + branch pipelines)
# This is a very common pattern:
workflow:
  rules:
    - if: $CI_PIPELINE_SOURCE == "merge_request_event"
    - if: $CI_COMMIT_BRANCH && $CI_OPEN_MERGE_REQUESTS
      when: never   # skip branch pipeline when MR pipeline exists
    - if: $CI_COMMIT_BRANCH

Preventing duplicate pipelines: by default, pushing to a branch that has an open MR creates two pipelines - a branch pipeline and an MR pipeline. The pattern above suppresses branch pipelines when an MR is open, avoiding redundant CI runs that waste runner minutes.

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