cache/restore/README.md

Restore action

The restore action restores a cache. It works similarly to the cache action except that it doesn't have a post step to save the cache. This action provides granular ability to restore a cache without having to save it. It accepts the same set of inputs as the cache action.

Documentation

Inputs

• key - An explicit key for a cache entry. See creating a cache key.
• path - A list of files, directories, and wildcard patterns to restore. See @actions/glob for supported patterns.
• restore-keys - An ordered list of prefix-matched keys to use for restoring stale cache if no cache hit occurred for key.
• fail-on-cache-miss - Fail the workflow if cache entry is not found. Default: false
• lookup-only - Check if a cache entry exists for the given input(s) (key, restore-keys) without downloading the cache. Default: false

Outputs

• cache-hit - A boolean value to indicate an exact match was found for the key.
• cache-primary-key - Cache primary key passed in the input to use in subsequent steps of the workflow.
• cache-matched-key - Key of the cache that was restored, it could either be the primary key on cache-hit or a partial/complete match of one of the restore keys.

Note

cache-hit will be set to true only when cache hit occurs for the exact key match. For a partial key match via restore-keys or a cache miss, it will be set to false.

Environment Variables

• SEGMENT_DOWNLOAD_TIMEOUT_MINS - Segment download timeout (in minutes, default 60) to abort download of the segment if not completed in the defined number of minutes. Read more

Use cases

As this is a newly introduced action to give users more control in their workflows, below are some use cases where one can use this action.

Only restore cache

If you are using separate jobs to create and save your cache(s) to be reused by other jobs in a repository, this action will take care of your cache restoring needs.

steps:
  - uses: actions/checkout@v3

  - uses: actions/cache/restore@v3
    id: cache
    with:
      path: path/to/dependencies
      key: ${{ runner.os }}-${{ hashFiles('**/lockfiles') }}

  - name: Install Dependencies
    if: steps.cache.outputs.cache-hit != 'true'
    run: /install.sh

  - name: Build
    run: /build.sh

  - name: Publish package to public
    run: /publish.sh

Once the cache is restored, unlike actions/cache, this action won't run a post step to do post-processing, and the rest of the workflow will run as usual.

Save intermediate private build artifacts

In case of multi-module projects, where the built artifact of one project needs to be reused in subsequent child modules, the need to rebuild the parent module again and again with every build can be eliminated. The actions/cache or actions/cache/save action can be used to build and save the parent module artifact once, and it can be restored multiple times while building the child modules.

Step 1 - Build the parent module and save it

steps:
  - uses: actions/checkout@v3

  - name: Build
    run: /build-parent-module.sh

  - uses: actions/cache/save@v3
    id: cache
    with:
      path: path/to/dependencies
      key: ${{ runner.os }}-${{ hashFiles('**/lockfiles') }}

Step 2 - Restore the built artifact from cache using the same key and path

steps:
  - uses: actions/checkout@v3

  - uses: actions/cache/restore@v3
    id: cache
    with:
      path: path/to/dependencies
      key: ${{ runner.os }}-${{ hashFiles('**/lockfiles') }}

  - name: Install Dependencies
    if: steps.cache.outputs.cache-hit != 'true'
    run: /install.sh

  - name: Build
    run: /build-child-module.sh

  - name: Publish package to public
    run: /publish.sh

Exit workflow on cache miss

You can use fail-on-cache-miss: true to exit a workflow on a cache miss. This way you can restrict your workflow to only build when there is a cache-hit.

To fail if there is no cache hit for the primary key, leave restore-keys empty!

steps:
  - uses: actions/checkout@v3

  - uses: actions/cache/restore@v3
    id: cache
    with:
      path: path/to/dependencies
      key: ${{ runner.os }}-${{ hashFiles('**/lockfiles') }}
      fail-on-cache-miss: true

  - name: Build
    run: /build.sh

Tips

Reusing primary key and restored key in the save action

Usually you may want to use the same key with both actions/cache/restore and actions/cache/save actions. To achieve this, use outputs from the restore action to reuse the same primary key (or the key of the cache that was restored).

Using restore action outputs to make save action behave just like the cache action

The outputs cache-primary-key and cache-matched-key can be used to check if the restored cache is same as the given primary key. Alternatively, the cache-hit output can also be used to check if the restored was a complete match or a partially restored cache.

Ensuring proper restores and save happen across the actions

It is very important to use the same key and path that were used by either actions/cache or actions/cache/save while saving the cache. Learn more about cache key naming and versioning here.