GitHub Actions / GitLab CI

Modern CI/CD is a build-and-test-in-code paradigm, and GitHub Actions and GitLab CI are the two platforms that have won. GitHub Actions' marketplace has 30,000+ reusable actions and tight integration with the world's largest code host. GitLab CI's advantage is a truly integrated platform (code + CI + registry + security scanning in one product), which reduces vendor sprawl for self-hosted teams. The critical DevOps skill here is not writing pipelines — it's understanding caching strategies (Docker layer caching, dependency caching), matrix builds, and reusable workflow patterns. Poorly designed pipelines are the single biggest source of developer productivity loss: a 15-minute CI build that could be 4 minutes with proper caching costs teams thousands of engineer-hours annually.