Debug-action-cache ((exclusive))

What is debug-action-cache?

debug-action-cache is not a standalone command but rather a diagnostic technique used to inspect, validate, and troubleshoot how GitHub Actions (or similar CI systems) save and restore cached dependencies, build artifacts, or intermediate files. It helps answer:
"Why is my cache miss happening?" or "What exactly is stored in this cache?"

It typically involves:

  1. Enabling step debug logging (runner diagnostic logging).
  2. Using the ACTIONS_RUNNER_DEBUG and ACTIONS_STEP_DEBUG secrets.
  3. Manually inspecting cache contents via API or temporary debug jobs.

Part 1: The Anatomy of CI Caching

Before we debug, we must understand the architecture. When a CI job runs, it typically starts in a fresh, ephemeral environment. Without caching, every job would re-download dependencies (npm, pip, Maven, apt), re-compile code, or re-pull Docker layers. debug-action-cache

4. Advanced Debugging: Isolating the Cache

If you suspect the cache is corrupted or causing flaky builds, perform an isolation test.

Strategy: Force a Cache Miss Modify the key temporarily to force the creation of a fresh cache. What is debug-action-cache

key: debug-test-$ github.run_id -$ hashFiles('**/package-lock.json')
  • $ github.run_id ensures a unique key every run.
  • If the build succeeds with this unique key but fails with the standard key, your previous cache was corrupted or stale.

Part 4: Advanced debug-action-cache Techniques

Once you have basic visibility, you can move to advanced diagnostics.

Understanding and Debugging action-cache in GitHub Actions

In the context of Continuous Integration (CI) with GitHub Actions, the term debug-action-cache usually refers to the process of troubleshooting the GitHub Actions Cache mechanism. Developers often encounter issues where caches are not saving, not restoring, or growing too large. Enabling step debug logging (runner diagnostic logging)

This write-up covers the mechanics of the cache, common failure modes, and actionable strategies to debug caching issues.

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