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Created June 26, 2025 15:36
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Jenkins to GitHub Actions Planning
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README.md

Migrating from CloudBees Jenkins to GitHub Actions

Goal: Migrate Jenkins to GitHub Actions while minimizing downtime, and maintaining CI/CD continuity.

Phase 1: Discovery & Assessment

Objectives: Understand current state, identify gaps, and define migration scope.

  1. Inventory Jenkins Environment:

    • Audit all Jenkins jobs:
      • Freestyle vs. Pipeline jobs.
      • Dependencies (plugins, shared libraries, external scripts).
      • Frequency, complexity, and runtime.
    • Catalog integrations (SCM, artifact repos, notifications, deployment targets).
    • Document security/access controls (credentials, RBAC).
    • Tool: Jenkins API, job-dsl-plugin, or custom scripts.

  2. Assess GitHub Actions Readiness:

    • Map Jenkins features to GitHub Actions:
      • Plugins → GitHub Actions Marketplace equivalents (e.g., actions/checkout for SCM).
      • Shared libraries → Reusable workflows/composite actions.
      • Agents → GitHub-hosted vs. self-hosted runners.
    • Identify gaps (e.g., niche plugins) and solutions (custom actions, SaaS tools).
    • Review GitHub rate limits, concurrency, and storage quotas.

  3. Stakeholder Alignment:

    • Define migration priorities (e.g., non-critical jobs first).
    • Establish success metrics (e.g., build time, failure rate, cost savings).

Phase 2: Strategy & Design

Objectives: Design migration approach, governance, and testing framework.

  1. Migration Strategy:

    • Phased Rollout:
      • Group jobs by team/project complexity (e.g., low-risk CI jobs → CD pipelines).
      • Use feature flags to toggle between Jenkins/GitHub Actions during transition.
    • Parallel Run Model:
      • Run GitHub Actions workflows alongside Jenkins for validation (compare outputs/logs).
    • Self-Hosted Runners:
      • Deploy GitHub Actions runners on existing Jenkins agent infrastructure (reuse VMs/containers).

  2. Workflow Design:

    • Convert Jenkins Pipelines to GitHub Actions:
      • Rebuild Jenkinsfile as .github/workflows/*.yml.
      • Use actions/cache for dependency caching.
    • Standardize templates for:
      • Builds (e.g., Maven/Gradle).
      • Deployments (e.g., Kubernetes/Cloud).
      • Notifications (Slack/Teams).
    • Secrets Management: Migrate Jenkins credentials to GitHub Secrets or HashiCorp Vault.

  3. Governance & Security:

    • Branch protection rules, required approvals, and environment safeguards.
    • Audit logging via GitHub Audit Log.

Phase 3: Tooling & Environment Setup

Objectives: Automate migration and prepare GitHub environment.

  1. Migration Automation:

    • Develop scripts to:
      • Convert Jenkins jobs to Actions workflows (e.g., using jenkins-to-actions converters).
      • Migrate job history/logs (if critical) via GitHub API.
    • Implement CI/CD for GitHub Actions workflows (e.g., linting with actionlint).

  2. GitHub Environment:

    • Set up organizations/repositories with team-based permissions.
    • Configure self-hosted runners:
      • Use Kubernetes or Docker for scalable runner pools.
      • Label runners by OS/environment (e.g., linux-prod).
    • Integrate with existing toolchain:
      • Artifactory/Nexus → actions/upload-artifact.
      • Jira → Marketplace actions.

Phase 4: Pilot Migration

Objectives: Validate approach with low-risk jobs.

  1. Select Pilot Jobs:

    • Start with 5–10% of jobs (e.g., linters, unit tests).
    • Avoid business-critical/CD pipelines initially.

  2. Execution & Validation:

    • Run parallel Jenkins/GitHub Actions jobs.
    • Compare:
      • Build artifacts.
      • Test coverage reports.
      • Execution time/costs.
    • Solicit feedback from pilot teams.

  3. Refine Approach:

    • Adjust templates, runner scaling, and error handling.
    • Document lessons learned.

Phase 5: Full Migration

Objectives: Migrate all remaining jobs in waves.

  1. Wave-Based Execution:

    • Wave 1: Non-production jobs (20% of workloads).
    • Wave 2: Production CI jobs (40%).
    • Wave 3: CD pipelines (40%).
    • Schedule per team to minimize disruption.

  2. Automated Testing & Rollback:

    • Post-migration smoke tests for each workflow.
    • Rollback plan: Revert to Jenkins if critical failures occur.

  3. Decommission Jenkins:

    • Redirect webhooks/triggers to GitHub.
    • Archive Jenkins data post-stabilization (1–2 weeks).

Phase 6: Optimization & Governance

Objectives: Improve efficiency and enforce standards.

  1. Optimize GitHub Actions:

    • Reduce runtime via dependency caching.
    • Refactor monolith jobs into reusable workflows.
    • Monitor costs with GitHub Insights.

  2. Training & Documentation:

    • Workshops for developers on Actions syntax/debugging.
    • Playbooks for common issues (e.g., runner offline, quota limits).

  3. Continuous Improvement:

    • Quarterly reviews of failure rates/build times.
    • Adopt new Actions features (e.g., matrix builds).

Key Risks & Mitigation

Risk Mitigation
Job conversion errors Pilot testing; manual review of complex jobs
Plugin gaps Build custom actions; use SaaS alternatives
Downtime during cutover Parallel runs; off-peak migrations
Team resistance Training; assign "Actions champions" per team
Cost overruns Monitor runner usage; right-size VMs

Timeline & Resources

  • Total Duration:
  • Team:
    • Project Manager (oversight).
    • DevOps Engineers (migration, automation).
    • Security Engineer (governance).
    • Developer Champions (per team).

Success Metrics

  • 100% of jobs migrated with zero data loss.
  • 20% faster median build time.
  • 30% reduction in CI/CD costs.
  • 95%+ developer satisfaction (post-migration survey).

Final Notes:

  • Use GitHub’s Actions Importer for automated Jenkins-to-Actions conversion.
  • Engage GitHub Premium Support for quota/scaling discussions.
  • Documentation Hub: Maintain a centralized wiki for standards, templates, and FAQs.

This plan ensures a controlled, low-risk transition while maximizing GitHub’s ecosystem benefits. Adjust phases based on organizational size and complexity.

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