Dockerfile: cache build artifacts

Dockerfile

@@ -1,26 +1,30 @@
-FROM joystream/rust-builder AS node-build
-LABEL description="Compiles joystream substrate node"
-
+# syntax=docker/dockerfile:experimental
+# must enable experimental features in docker daemon and set DOCKER_BUILDKIT=1 env variable
+# https://github.com/moby/buildkit/blob/master/frontend/dockerfile/docs/experimental.md
+FROM joystream/rust-builder AS builder
+LABEL description="compiles and caches dependencies, artifacts and node"
 WORKDIR /joystream
-# if source files change will the intermediate image be rebuilt?
 COPY . /joystream
-ENV TERM=xterm
+RUN mkdir /build-output
 
-RUN cargo build --release
+RUN --mount=type=cache,target=/joystream/target \
+    --mount=type=cache,target=/root/.cargo/git \
+    --mount=type=cache,target=/root/.cargo/registry \
+    cargo build --release \
+    && cp ./target/release/joystream-node /build-output/joystream-node
+# copy in last part could be done with nightly option --out-dir
 
 FROM debian:stretch
 LABEL description="Joystream node"
-
 WORKDIR /joystream
-ENV TERM=xterm
-
-COPY --from=node-build /joystream/target/release/joystream-node /joystream
+COPY --from=builder /build-output/joystream-node /joystream/node
 
 # Use these volumes to persits chain state and keystore, eg.:
 # --base-path /data
 # optionally separate keystore (otherwise it will be stored in the base path)
 # --keystore-path /keystore
-# if basepath isn't specified it will be inside container in ~/.local/share/joystream-node/
+# if base-path isn't specified, chain state is stored inside container in ~/.local/share/joystream-node/
+# which is not ideal
 VOLUME ["/data", "/keystore"]
 
-ENTRYPOINT ["/joystream/joystream-node"]
+ENTRYPOINT ["/joystream/node"]