Use multi-stage build in Dockerfile

#300.

.dockerignore

@@ -2,7 +2,6 @@
 #
 # SPDX-License-Identifier: CC0-1.0
 
-.git
 node_modules
 config
 lib

Dockerfile

@@ -3,19 +3,24 @@
 #
 # SPDX-License-Identifier: Apache-2.0 AND AFL-3.0
 
-# We can't use alpine anymore because crypto has rust deps.
-FROM node:20-slim
+FROM alpine/git:latest as git-stamp-stage
 COPY . /tmp/src
+RUN cd /tmp/src && git describe > version.txt.tmp && mv version.txt.tmp version.txt
+
+FROM node:20-slim as build-stage
+COPY . /tmp/src
+COPY --from=git-stamp-stage /tmp/src/version.txt version.txt
 RUN cd /tmp/src \
-    && yarn install --network-timeout 100000 \
+    && yarn install --frozen-lockfile --network-timeout 100000 \
     && yarn build \
-    && mv lib/ /mjolnir/ \
-    && mv node_modules / \
-    && mv mjolnir-entrypoint.sh / \
-    && mv package.json / \
-    && mv version.txt / \
-    && cd / \
-    && rm -rf /tmp/*
+    && yarn install --frozen-lockfile --production --network-timeout 100000
+
+FROM node:20-slim as final-stage
+COPY --from=git-stamp-stage /tmp/src/version.txt version.txt
+COPY --from=build-stage /tmp/src/lib/ /mjolnir/
+COPY --from=build-stage /tmp/src/node_modules /node_modules
+COPY --from=build-stage /tmp/src/mjolnir-entrypoint.sh /
+COPY --from=build-stage /tmp/src/package.json /
 
 ENV NODE_ENV=production
 ENV NODE_CONFIG_DIR=/data/config