Serve checkouts from pre-warmed repository clones

Keep repository clones warm on a few machines and run Git operations against them, so jobs skip the cold clone.

Prompt

Evaluate and apply this CI technique to my repository: Serve checkouts from pre-warmed repository clones.

Keep repository clones warm on a few machines and run Git operations against them, so jobs skip the cold clone.

Read the technique and its source-backed company examples: https://starsling.dev/ci-playbooks/techniques/git-checkout-service.md

Inspect this repository’s CI workflows, build and test commands, dependencies, and recent run timings. Identify where this technique applies and explain the expected benefit using this repository’s evidence.
Measure a baseline from recent comparable runs: elapsed time, queue time, runner minutes and failures where available. If data is unavailable, say what cannot be measured.
Compare relevant company approaches, checking prerequisites, platform differences and tradeoffs. Rank applicable options by evidence, fit and measurable opportunity; do not present company results as predictions for this repo.
Recommend the smallest safe change, show what checks and fallback paths remain, and ASK ME WHICH CHANGE TO APPROVE BEFORE EDITING ANY FILES.
Only after approval, work on a new feature branch, make one reversible change, and open a reviewable pull request. Never merge or push to a default or protected branch.
Keep required checks, test coverage, deployment and release behavior intact. Validate the change and compare equivalent runs where possible; report limitations and what should be monitored after merge.

View all playbooks

How Uber used this technique

Read what Uber changed and follow the original sources.

Serve checkouts from pre-warmed repository clones

Translated to GitHub Actions

What Uber built: Uber's GitFarm serves checkouts from pre-warmed bare clones, so clients get a full Git checkout in under 500 milliseconds.
Your GitHub Actions version: Check out from a pre-warmed repository clone or a shallow fetch, sized to what the job reads.

Cloning Uber's Go monorepo takes roughly 15 minutes and consumes around 6 CPU cores, 32 GB of memory and over 40 GB of disk. GitFarm runs standard Git commands for other services inside ephemeral sandboxes backed by pre-warmed repository checkouts. Each backend keeps one bare clone per repository, updated by push-based events with a fetch every 5 minutes behind them. Clients get a full Git checkout in under 500 milliseconds and no local clone.

Uber reports that clients get a full Git checkout in under 500 milliseconds, and services no longer suffer cold starts of 10-15 minutes due to initial clones on each host. Source

Uber reports a CODEOWNERS service's startup time going from 15-20 minutes to under 1 minute, and its CPU from over 70 cores to 16 cores, after switching to GitFarm API calls. Source

Use it when: Many jobs or services clone the same large repository, and each pays for the clone and adds load on the Git server.
Before applying it: Freshness is eventually consistent with the upstream repository, so let a caller ask for the latest state when a job needs it.
GitHub Actions adaptation: Compare the source system with your own workflow before applying this translation.

How Uber used this technique

Serve checkouts from pre-warmed repository clones

Related techniques

Fetch only the repository history a job needs

Keep full history and download old blobs on demand

Bake stable dependencies into runner images

Company Playbooks

Related guides

Filter workflows by changed files

Cancel superseded CI runs