fix: Avoid unnecessary re-work in docker build

.gitlab-ci.yml

@@ -29,28 +29,22 @@ test:
 build_image_for_commit:
   stage: test
   image: "docker:20.10"
-  only:
-    - master
   cache:
     paths:
       - _build/
       - deps/
   services:
     - name: docker:20.10-dind
-  script:
+  before_script:
     - docker login "https://${CI_REGISTRY}" -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD
     - docker pull $CI_REGISTRY_IMAGE:latest || true
+  script:
     # This enables fast parallel builds
     - export DOCKER_BUILDKIT=1
-    - mkdir -p _build/prod
     - docker build --cache-from $CI_REGISTRY_IMAGE:latest -t $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA .
     # Push the commit SHA tagged version to registry. We will later choose to tag that as stable
     #   if everything passes.
     - docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
-    # Pull out the built _build/prod directory so we can cache it!
-    - CONTAINER_HANDLE=`docker create $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA`
-    - docker cp $CONTAINER_HANDLE:/root/app/_build/prod _build
-    - docker cp $CONTAINER_HANDLE:/root/app/deps deps
 
 # If tests pass, tag the commit and update package versions
 deploy_to_tags:

Dockerfile

@@ -1,10 +1,5 @@
 FROM elixir:1.10.4-alpine AS elixir1
 
-RUN apk add make gcc libc-dev
-
-ENV CC=gcc
-ENV MIX_HOME=/opt/mix
-
 RUN mix local.hex --force \
   && mix local.rebar --force
 
@@ -21,23 +16,18 @@ WORKDIR /root/app
 
 # We load these things one by one so that we can load the deps first and
 #   cache those layers, before we do the app build itself
-ADD ./config /root/app/config
-ADD ./mix.exs /root/app/
-ADD ./mix.lock /root/app/
-ADD ./apps/admin/mix.exs /root/app/apps/admin/
-ADD ./apps/app/mix.exs /root/app/apps/app/
-ADD ./apps/content/mix.exs /root/app/apps/content/
-ADD ./apps/core/mix.exs /root/app/apps/core/
-ADD ./_build/${MIX_ENV}/ /root/app/_build/${MIX_ENV}/
-ADD ./deps/ /root/app/deps/
-ADD ./script/ /root/app/script/
-RUN script/restore-timestamps
+ADD ./mix.exs ./mix.lock ./
+ADD ./config ./config
+ADD ./apps/admin/mix.exs ./apps/admin/
+ADD ./apps/app/mix.exs ./apps/app/
+ADD ./apps/content/mix.exs ./apps/content/
+ADD ./apps/core/mix.exs ./apps/core/
+
 RUN mix deps.get
-RUN mix deps.compile
 
 # Leave off here so that we can built assets and compile the elixir app in parallel
 
-FROM node:15.0
+FROM node:15.0 AS asset-builder
 
 # Build assets in a node container
 ADD ./apps/app/assets/ /root/app/apps/app/assets/
@@ -49,17 +39,15 @@ RUN npm run deploy
 
 FROM elixir1
 
+RUN mix deps.compile
+
 ADD ./apps /root/app/apps
 
 # Resume compilation of the elixir app
 RUN MAKE=cmake mix compile
 
 # Copy in the built assets & fingerprint them
-COPY --from=1 /root/app/apps/app/priv/static/ /root/app/apps/app/priv/static
+COPY --from=asset-builder /root/app/apps/app/priv/static/ /root/app/apps/app/priv/static
 RUN mix phx.digest
 
-RUN script/restore-timestamps
-
-RUN mkdir -p /root/app/priv/
-
 CMD elixir --name ${NAME:=legendary}@$(hostname -f) -S mix phx.server