Cache backend API example

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

docs/advanced/cache.md

@@ -1,13 +1,18 @@
 # Cache
 
+* [Inline cache](#inline-cache)
 * [Registry cache](#registry-cache)
 * [GitHub cache](#github-cache)
+  * [Cache backend API](#cache-backend-api)
+  * [Local cache](#local-cache)
 
-> More info about buildx cache: https://github.com/docker/buildx/blob/master/docs/reference/buildx_build.md#cache-from
+> More info about cache on [BuildKit](https://github.com/moby/buildkit#export-cache) and [Buildx](https://github.com/docker/buildx/blob/master/docs/reference/buildx_build.md#cache-from) repositories.
 
-## Registry cache
+## Inline cache
 
-You can import/export cache from a cache manifest or (special) image configuration on the registry.
+In most case you want to use the [`type=inline` cache exporter](https://github.com/moby/buildkit#inline-push-image-and-cache-together).
+However, note that the `inline` cache exporter only supports `min` cache mode. To enable `max` cache mode, push the
+image and the cache separately by using the `registry` cache exporter as shown in the [next example](#registry-cache).
 
 ```yaml
 name: ci
@@ -44,16 +49,104 @@ jobs:
           cache-to: type=inline
 ```
 
+## Registry cache
+
+You can import/export cache from a cache manifest or (special) image configuration on the registry with the
+[`type=registry` cache exporter](https://github.com/crazy-max/buildkit/tree/cache-docs#registry-push-image-and-cache-separately).
+
+```yaml
+name: ci
+
+on:
+  push:
+    branches:
+      - 'master'
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v2
+      -
+        name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+      -
+        name: Login to DockerHub
+        uses: docker/login-action@v1 
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+      -
+        name: Build and push
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          push: true
+          tags: user/app:latest
+          cache-from: type=registry,ref=user/app:buildcache
+          cache-to: type=registry,ref=user/app:buildcache,mode=max
+```
+
 ## GitHub cache
 
+### Cache backend API
+
+> :test_tube: This cache exporter is considered EXPERIMENTAL until further notice. Please provide feedback on
+> [BuildKit repository](https://github.com/moby/buildkit) if you encounter any issues.
+
+Since [buildx 0.6.0](https://github.com/docker/buildx/releases/tag/v0.6.0) and [BuildKit 0.9.0](https://github.com/moby/buildkit/releases/tag/v0.9.0),
+you can use the [`type=gha` cache exporter](https://github.com/moby/buildkit/tree/master#github-actions-cache-experimental).
+
+GitHub Actions cache exporter backend uses the [GitHub Cache API](https://github.com/tonistiigi/go-actions-cache/blob/master/api.md)
+to fetch and upload cache blobs. That's why this type of cache should be exclusively used in a GitHub Action workflow
+as the `url` (`$ACTIONS_CACHE_URL`) and `token` (`$ACTIONS_RUNTIME_TOKEN`) attributes are populated when a workflow
+is started.
+
+```yaml
+name: ci
+
+on:
+  push:
+    branches:
+      - 'master'
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v2
+      -
+        name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+      -
+        name: Login to DockerHub
+        uses: docker/login-action@v1 
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+      -
+        name: Build and push
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          push: true
+          tags: user/app:latest
+          cache-from: type=gha
+          cache-to: type=gha,mode=max
+```
+
+### Local cache
+
 > :warning: At the moment caches are copied over the existing cache so it [keeps growing](https://github.com/docker/build-push-action/issues/252).
 > The `Move cache` step is used as a temporary fix (see https://github.com/moby/buildkit/issues/1896).
 
-> :rocket: There is a new cache backend using GitHub cache being developed that will lighten your workflow.
-> More info: https://github.com/docker/buildx/pull/535
-
-You can leverage [GitHub cache](https://docs.github.com/en/actions/configuring-and-managing-workflows/caching-dependencies-to-speed-up-workflows)
-using [actions/cache](https://github.com/actions/cache) with this action:
+You can also leverage [GitHub cache](https://docs.github.com/en/actions/configuring-and-managing-workflows/caching-dependencies-to-speed-up-workflows)
+using [actions/cache](https://github.com/actions/cache) and [`type=local` cache exporter](https://github.com/moby/buildkit#local-directory-1)
+with this action:
 
 ```yaml
 name: ci
@@ -95,7 +188,7 @@ jobs:
           push: true
           tags: user/app:latest
           cache-from: type=local,src=/tmp/.buildx-cache
-          cache-to: type=local,dest=/tmp/.buildx-cache-new
+          cache-to: type=local,dest=/tmp/.buildx-cache-new,mode=max
       -
         # Temp fix
         # https://github.com/docker/build-push-action/issues/252