The pipeline YAML looks different between GitLab CI and GitHub Actions, but that's not the decision that matters most. The decision that actually affects your costs, your build times, and your security posture is: where do your runners execute, and who's responsible for them?
Managed runners
Both platforms offer managed runners — GitLab's shared runners, GitHub's hosted runners. Zero setup, billed per minute (or included up to a quota). For most teams under a few hundred build-minutes a month, this is the right default. You're trading a small per-minute cost for not having to patch, scale, or secure a runner fleet.
Self-hosted runners
Self-hosting pays off once you hit one of these: high build volume (managed-runner minutes get expensive fast), builds that need to reach private network resources (an internal artifact registry, a database only reachable from your VPC), or specific hardware (GPU builds, ARM builds for a Raspberry Pi fleet).
The cost you're accepting in exchange: someone has to patch the runner OS, rotate the runner registration token, and make sure a compromised build script can't reach anything it shouldn't. A self-hosted runner with docker.sock mounted in, run as root, on a box that also holds production SSH keys, is a real incident waiting to happen — we've seen it.
Caching — the thing everyone gets wrong first
Both platforms cache dependencies between runs, but the default cache key is often too broad or too narrow. Too broad (e.g. keyed only on branch name) and you're serving a stale node_modules after a package.json change. Too narrow (keyed on a full lockfile hash with no fallback key) and every dependency bump pays the full install cost with no partial reuse.
cache:
key:
files:
- package-lock.json
paths:
- node_modules/That's the GitLab CI form — key on the lockfile, so the cache invalidates exactly when dependencies change, not on every commit and not never.
Our default recommendation
Start on managed runners on whichever platform your repo already lives on. Move to self-hosted only when you've hit a specific, measured reason to — not because self-hosting feels more "real." We set up self-hosted runners as part of our CI/CD engagements when the numbers justify it, hardened from day one rather than retrofitted after an incident.