Introduce CI stages (front / back), mix format runs in parallel

.gitlab-ci.yml

 image: tcitworld/mobilizon-ci
 
-services:
-  - name: mdillon/postgis:10
-    alias: postgres
+stages:
+  - front
+  - back
 
 variables:
   MIX_ENV: "test"
@@ -12,24 +12,48 @@ variables:
   POSTGRES_HOST: postgres
   GEOLITE_CITIES_PATH: "/usr/share/GeoIP/GeoLite2-City.mmdb"
 
-cache:
-  paths:
-    - deps
-    - _build
-    - .rebar3
-    - ~/.mix
-    - ~/.hex
-    - js/node_modules
+js:
+  stage: front
+  before_script:
+    - cd js
+    - npm install
+  script:
+    - npm run build
+  after_script:
+    - cd ../
+  cache:
+    paths:
+      - js/node_modules
+  artifacts:
+    paths:
+      - priv/static
+    untracked: false
+    expire_in: 30 days
 
-before_script:
-  - cd js && npm install && npm run build && cd ../
-  - mix local.rebar --force
-  - mix local.hex --force
-  - mix deps.get
-  - MIX_ENV=test mix ecto.create
-  - MIX_ENV=test mix ecto.migrate
+elixir_format:
+  stage: back
+  before_script:
+    - mix deps.get
+  script:
+    - mix format --check-formatted --dry-run
+  cache:
+    paths:
+      - deps
 
 mix:
+  stage: back
+  services:
+  - name: mdillon/postgis:10
+    alias: postgres
+  dependencies:
+    - js
+  before_script:
+    - mix deps.get
+    - MIX_ENV=test mix ecto.create
+    - MIX_ENV=test mix ecto.migrate
   script:
-  - mix format --check-formatted --dry-run
-  - mix coveralls
+    - mix coveralls
+  cache:
+    paths:
+      - deps
+      - _build

docker/tests/Dockerfile

 FROM elixir:latest
+LABEL maintainer="Thomas Citharel <tcit@tcit.fr>"
 
+ENV REFRESHED_AT=2018-12-18
 RUN apt-get update -yq && apt-get install -yq build-essential inotify-tools postgresql-client git curl gnupg
-RUN curl -sL https://deb.nodesource.com/setup_8.x | bash && apt-get install nodejs -yq
+RUN curl -sL https://deb.nodesource.com/setup_10.x | bash && apt-get install nodejs -yq
 RUN apt-get clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
+RUN mix local.hex --force && mix local.rebar --force
 RUN curl http://geolite.maxmind.com/download/geoip/database/GeoLite2-City.tar.gz --output GeoLite2-City.tar.gz -s && tar zxf GeoLite2-City.tar.gz && mkdir -p /usr/share/GeoIP && mv GeoLite2-City_*/GeoLite2-City.mmdb /usr/share/GeoIP/GeoLite2-City.mmdb
\ No newline at end of file