On most modern platforms, including GitHub Actions, . Once a cache is saved under a specific key (e.g., node-modules-v1 ), it can never be updated or overwritten. If your dependencies change but your cache key remains the same, the runner will continue to pull the old, stale cache. This behavior is the root cause of most caching bugs and makes learning how to execute a debug-action-cache workflow essential.
: Use actions/cache/restore and actions/cache/save as separate steps to identify if the failure is during download or upload. 📊 Sample Debug Report Data
To debug a cache effectively, you must first understand how GitHub Actions and similar CI/CD platforms manage the cache lifecycle. A typical caching mechanism consists of three distinct phases:
[debug] Restoring cache... (originally saved on windows-2022) [debug] Extracting binary: 'app.exe' -> incompatible. debug-action-cache
Better yet, use inside the key to invalidate automatically when needed.
Inspect the execution logs of your caching step. You are looking for one of three outcomes:
: If you require that the cache always be saved, you must abandon the all-in-one actions/cache action and use the more granular restore and save actions separately. By splitting the logic, you can control the save step with an if: always() condition to ensure it executes regardless of prior failures. On most modern platforms, including GitHub Actions,
Create a secret named ACTIONS_STEP_DEBUG with value true (Settings > Secrets and variables > Actions > New repository secret). This activates debug mode for all workflows without modifying YAML files.
[CI Run Begins] │ ▼ ┌───────────┐ Yes ┌─────────────────────────┐ │ Cache Key ├───────────────────►│ Restore Pre-built State │ │ Match? │ [Cache Hit] │ (Skip Compilation/Deps) │ └─────┬─────┘ └─────────────────────────┘ │ No │ [Cache Miss] ▼ ┌─────────────────────────┐ │ Fetch & Build Fresh │ ├─────────────────────────┤ │ Generate New Cache Key │ ├─────────────────────────┤ │ Upload Artifact to Store│ └─────────────────────────┘
debug-action-cache is a caching mechanism designed to store and reuse the results of expensive computations or actions during the development process. It's particularly useful in Continuous Integration/Continuous Deployment (CI/CD) pipelines, where repeated computations or actions can significantly slow down the build process. This behavior is the root cause of most
The first step is determining why a cache miss occurred when a hit was expected. Most modern build tools provide execution logs or "cache-miss" reports. By comparing the hash of a local action against the hash stored in the cache, developers can identify the specific file or environment variable that caused the discrepancy.
Source files that change on every build (e.g., a file containing a build timestamp).