Analysis: Job difference between pipelines on backports and on stable branches

Analyze

The number of jobs vastly differs between pipelines executed at the merge request (pre-merge) level and on stable branches (post-merge). To understand the difference, I created a brief ruby script to fetch the jobs from each pipeline. Outcome:

• The pre-merge pipeline has 765 jobs, while the post-merge pipeline contains 297
• Jobs included in the pre-merge pipeline include almost all the jobs of the post-merge pipeline
• Pre-merge pipeline includes several downstream pipelines to test different end-to-end workflows (e2e:test-product-analytics, e2e:test-on-gdk, e2e:test-on-omnibus-ee, start-as-if-foss)
• Post-merge pipeline includes release environments.

Note the post-merge pipeline is analyzed on the security side to include the release environments jobs.

Open questions:

• Can it be assumed the pre-merge pipeline will always include the jobs of the post-merge pipeline?
• Jobs on pre-merge pipelines can vary, for example, other pipelines have 403 jobs and 593 jobs respectively. What is the difference between these two?

Details

Jobs included on the pipeline but not at merge request:

jobs_stable = ReleaseTools::GitlabClient.pipeline_jobs(project, 1715473122).auto_paginate
jobs_merge_request = ReleaseTools::GitlabClient.pipeline_jobs(project.security_path, 1715476070).auto_paginate
jobs_stable.map(&:name) - jobs_merge_request.map(&:name)
=> ["sync-stable-branch"]

Jobs that are on merge request but not in the pipeline:

Click to expand

jobs_stable = ReleaseTools::GitlabClient.pipeline_jobs(project, 1715473122).auto_paginate
jobs_merge_request = ReleaseTools::GitlabClient.pipeline_jobs(project.security_path, 1715476070).auto_paginate
jobs_merge_request.map(&:name) - jobs_stable.map(&:name)
=> ["notify-test-on-omnibus-failure",
 "fail-pipeline-early",
 "rspec:merge-auto-explain-logs",
 "rspec:undercoverage",
 "rspec:coverage",
 "rspec:artifact-collector as-if-foss",
 "rspec rspec-ee-pg14-rerun-previous-failed-tests",
 "rspec rspec-pg14-rerun-previous-failed-tests",
 "rspec-ee fail-fast",
 "rspec fail-fast",
 "rspec-ee system pg14 single-db-ci-connection 16/16",
 "rspec-ee system pg14 single-db-ci-connection 15/16",
 "rspec-ee system pg14 single-db-ci-connection 14/16",
 "rspec-ee system pg14 single-db-ci-connection 13/16",
 "rspec-ee system pg14 single-db-ci-connection 12/16",
 "rspec-ee system pg14 single-db-ci-connection 11/16",
 "rspec-ee system pg14 single-db-ci-connection 10/16",
 "rspec-ee system pg14 single-db-ci-connection 9/16",
 "rspec-ee system pg14 single-db-ci-connection 8/16",
 "rspec-ee system pg14 single-db-ci-connection 7/16",
 "rspec-ee system pg14 single-db-ci-connection 6/16",
 "rspec-ee system pg14 single-db-ci-connection 5/16",
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 "rspec-ee system pg14 single-db 14/16",
 "rspec-ee system pg14 single-db 13/16",
 "rspec-ee system pg14 single-db 12/16",
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 "rspec-ee migration pg14 single-db 2/2",
 "rspec-ee migration pg14 single-db 1/2",
 "rspec-ee unit gitlab-duo-chat-qa pg14",
 "rspec-ee unit gitlab-duo-chat-zeroshot pg14",
 "rspec fast_spec_helper",
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 "db:docs-up-to-date",
 "db:gitlabcom-database-testing",
 "db:migrate-non-superuser",
 "db:post_deployment_migrations_validator-single-db",
 "db:post_deployment_migrations_validator",
 "db:check-migrations-single-db",
 "db:check-migrations",
 "db:check-schema-single-db",
 "db:check-schema",
 "db:migrate:reset single-db",
 "db:rollback single-db",
 "db:post_deployment_migrations_validator-single-db-ci-connection",
 "db:check-schema-single-db-ci-connection",
 "db:migrate:reset single-db-ci-connection",
 "db:rollback single-db-ci-connection",
 "jest-with-fixtures vue3 check quarantined 1/1",
 "jest vue3 check quarantined 4/4",
 "jest vue3 check quarantined 3/4",
 "jest vue3 check quarantined 2/4",
 "jest vue3 check quarantined 1/4",
 "ping-appsec-for-sast-findings",
 "semgrep-appsec-custom-rules",
 "build-gdk-image",
 "e2e-test-pipeline-generate",
 "detect-previous-failed-tests",
 "detect-tests",
 "set-pipeline-name",
 "rspec-predictive:pipeline-generate",
 "gdk:compile-test-assets",
 "delete-as-if-foss-environment",
 "delete-as-if-foss-branch",
 "prepare-as-if-foss-env",
 "prepare-as-if-foss-branch",
 "danger-review dry-run",
 "danger-review",
 "pipeline-tier-3"]

Bridge jobs included in pre-merge but not post-merge

[38] pry(main)> bridge_merge.map(&:name) - bridge_stable.map(&:name)
=> ["e2e:test-product-analytics", "e2e:test-on-gdk", "e2e:test-on-omnibus-ee", "start-as-if-foss"]

Bridge jobs included in post-merge but not pre-merge

[37] pry(main)> bridge_stable.map(&:name) - bridge_merge.map(&:name)
=> ["start-release-environments-security-pipeline"]

Analysis Outcome

There is a difference between pipelines on backports and stable branches due to the behavior of our MR pipelines.

The jobs that are run in a backport pipeline are majorly affected by the changes in the MR.

For instance, updating a gem will trigger certain jobs and not have other jobs. The same is true for other changes (frontend, backend, tooling, etc). This results in the job counts being very different, but predictable.

The backport MR (pre-merge) pipeline is essentially a sub-set of the stable branch (post-merge) pipeline. The post-merge pipeline is designed to be one of the last quality gates before release, resulting in the post-merge pipeline often having more jobs and running longer.