dev.Dockerfile: use cache mounts to speed up rebuilding

dev.Dockerfile

@@ -18,7 +18,13 @@ RUN apk add --no-cache --update alpine-sdk \
 COPY . /go/src/github.com/lightningnetwork/lnd
 
 #  Install/build lnd.
-RUN cd /go/src/github.com/lightningnetwork/lnd \
+# Note: When using `docker build`, setting the environmental variable
+# `DOCKER_BUILDKIT=1` is required to enable
+# [BuildKit](https://docs.docker.com/build/buildkit)
+# so that the cache mounts can be used.
+RUN --mount=type=cache,target=/go/pkg/mod \
+    --mount=type=cache,target=/root/.cache/go-build \
+    cd /go/src/github.com/lightningnetwork/lnd \
     &&  make \
     &&  make install-all tags="signrpc walletrpc chainrpc invoicesrpc peersrpc kvdb_sqlite"
 

docs/release-notes/release-notes-0.22.0.md

@@ -100,6 +100,17 @@
 
 ## Tooling and Documentation
 
+* [`dev.Dockerfile` now uses](https://github.com/lightningnetwork/lnd/pull/10903)
+  [cache mounts](https://docs.docker.com/build/cache/optimize/#use-cache-mounts)
+  to cache the `GOMODCACHE` and `GOCACHE` directories so that dependencies don't
+  need to be re-downloaded and re-built every time the image is re-created.
+  As a result of this change, `dev.Dockerfile` now requires
+  [BuildKit](https://docs.docker.com/build/buildkit) to build. When using
+  `docker build`, this can be enabled by setting the environmental variable
+  `DOCKER_BUILDKIT=1`. BuildKit also does not unnecessarily rebuild images when
+  the build context is a remote git repository because COPY layers are more
+  smartly compared to cache.
+
 # Contributors (Alphabetical Order)
 
 * bitromortac