Merge pull request #4635 from hiepxanh/patch-1

Add buildkit cache example to Dockerfile docs

docs/deployment/builders/dockerfiles.md

@@ -77,6 +77,24 @@ RUN echo $NODE_ENV
 
 If your Dockerfile is using Docker engine's [buildkit](https://docs.docker.com/develop/develop-images/build_enhancements/) (not to be confused with buildpacks), then the `DOCKER_BUILDKIT=1` environment variable needs to be set. One way to do this is to edit `/etc/environment` on your dokku host and reboot your instance. Note, for complete build log output, you should also set `BUILDKIT_PROGRESS=plain` in the same file. 
 
+#### Buildkit directory caching
+
+Buildkit implements the `RUN --mount` option, enabling mount directory caches for `RUN` directives. The following is an example that mounts debian packaging related directories, which can speed up fetching of remote package data.
+
+```Dockerfile
+FROM debian:latest
+RUN --mount=target=/var/lib/apt/lists,type=cache \
+    --mount=target=/var/cache/apt,type=cache \
+    apt-get update \
+ && DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
+      git
+```
+
+Mount cache targets may vary depending on the tool in use, and users are encouraged to investigate the directories that apply for their language and framework.
+
+
+You would adjust the cache directory for whatever application cache you have, e.g. `/root/.pnpm-store/v3` for pnpm, `$HOME/.m2` for maven, or `/root/.cache` for golang.
+
 ### Customizing the run command
 
 By default no arguments are passed to `docker run` when deploying the container and the `CMD` or `ENTRYPOINT` defined in the `Dockerfile` are executed. You can take advantage of docker ability of overriding the `CMD` or passing parameters to your `ENTRYPOINT` setting `$DOKKU_DOCKERFILE_START_CMD`. Let's say for example you are deploying a base Node.js image, with the following `ENTRYPOINT`: