Migrating 200 Microservices from Jenkins to GitHub Actions in 3 Months

Our platform team managed a Jenkins cluster running over 200 pipelines for our microservices. Jenkins was running on a fleet of 40 EC2 instances, costing us roughly $25k/month in compute alone. We had 3 full-time engineers maintaining the Jenkins infrastructure, dealing with plugin updates, security patches, and flaky executors. Build times averaged 18 minutes and teams were constantly complaining about queue times during peak hours.

After a particularly bad week where Jenkins was down for 6 hours due to a corrupted plugin update, leadership approved the migration to GitHub Actions. We formed a 4-person migration squad. The biggest challenge was that each of the 200 pipelines had its own quirks — custom Groovy scripts, shared libraries, artifact caching patterns, and deployment hooks. We built a transpiler that converted 80% of Jenkinsfile syntax to GitHub Actions YAML, then manually handled the remaining 20%. We migrated in waves of 20-30 services, starting with the least critical.

The migration was completed in 11 weeks, one week ahead of schedule. Build times dropped from 18 minutes to 7 minutes average thanks to better caching and parallelism. Monthly CI/CD costs dropped from $25k to $12k. We eliminated the 3-person Jenkins maintenance burden. The transpiler we built was open-sourced and got 400 GitHub stars in the first month.