How to Schedule a Cache Warm-Up on the Default Branch in GitHub Actions

Scheduled runs execute on the default branch, which is exactly where a shared cache must live to be reused by PRs.

Caches are scoped to a branch, and PR runs read caches from the base branch. A cron job on the default branch reinstalls dependencies so the cache stays populated and unexpired.

Steps

• Schedule a daily cron (schedule runs on the default branch by design).
• Restore and save the cache keyed on the lockfile hash.
• Run npm ci so a save happens on a cache miss.

Workflow

on:
  schedule:
    - cron: '0 5 * * *'
jobs:
  warm-cache:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/cache@v4
        with:
          path: ~/.npm
          key: npm-${{ hashFiles('package-lock.json') }}
      - run: npm ci

Gotchas

• Caches unused for seven days are evicted; a daily warm-up keeps them alive.
• PR runs can read base-branch caches but cannot write them, so the warm-up must run on the default branch.

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