dev.Dockerfile: use cache mounts to speed up rebuilding

Author: ZZiigguurraatt

dev.Dockerfile

@@ -70,7 +70,13 @@ ARG NO_UI
 ARG CGO_ENABLED=1
 
 # Install dependencies and install/build lightning-terminal.
-RUN apk add --no-cache --update alpine-sdk make \
+# 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 \
+  apk add --no-cache --update alpine-sdk make \
   && cd /go/src/github.com/lightninglabs/lightning-terminal \
   # If a custom lnd version is supplied, force it now.
   && if [ -n "$LND_VERSION" ]; then \

docs/release-notes/release-notes-0.16.0.md

@@ -17,6 +17,19 @@
 
 ### Functional Changes/Additions
 
+* `dev.Dockerfile` now uses 
+  [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. This
+  is particularly useful when the build context is a remote git repo and not a
+  local filesystem, which often times causes a `COPY` layer cache and all the
+  subsequent build layer caches to be invalidated. 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`.
+
+
 ### Technical and Architectural Updates
 
 ## RPC Updates