Create a pica-ci base image built only once, should decrease overall build time

.gitlab-ci.yml

@@ -9,14 +9,35 @@ services:
     - docker:19.03.0-dind
 
 stages:
+    - pica-ci-base
     - metabuild
     - build
     - static_tests
     - dynamic_tests
     - deployment
 
-# build the container that further steps will run in in order to avoid duplicating instructions between steps
-metabuild:
+# build the base image used for all further steps : this is done only when pica-ci's Dockerfile is modified
+pica-ci-base:
+    stage: pica-ci-base
+    before_script:
+        - echo $REGISTRY_PROD_PASSWORD | docker login $REGISTRY_PROD -u $REGISTRY_PROD_USERNAME --password-stdin
+    script:
+        - docker build -f pica-ci-base/Dockerfile . -t $REGISTRY_PROD/pica-ci-base:latest
+        - docker push $REGISTRY_PROD/pica-ci-base:latest
+    after_script:
+        - docker logout $REGISTRY_PROD
+    tags: [build]
+    only:
+        changes:
+            - "pica-ci-base/*"
+        refs:
+            - master
+            - dev-ci
+            - tx-services-p19-test
+            - dev-sympa
+
+# create a image based on pica-ci with only a few environment variables added (which Dockerfile has been modified...)
+metabuid:
     stage: metabuild
     before_script:
         - echo $REGISTRY_PASSWORD | docker login $REGISTRY -u $REGISTRY_USERNAME --password-stdin

pica-ci-base/Dockerfile

+FROM docker:19.03.0
+
+RUN apk update && \
+    apk add build-base \
+    git \
+    gnupg \
+    iproute2 \
+    libffi-dev \
+    openssl-dev \
+    py-pip \
+    python2-dev \
+    sed \
+    wget && \
+    pip install docker-compose

pica-ci/Dockerfile

-FROM docker:19.03.0
+FROM registry.picasoft.net/pica-ci-base:latest
+&
 WORKDIR /workdir
 COPY . /workdir/
 
-RUN apk update && \
-    apk add build-base \
-            git \
-            gnupg \
-            iproute2 \
-            libffi-dev \
-            openssl-dev \
-            py-pip \
-            python2-dev \
-            sed \
-            wget && \
-    pip install docker-compose && \
-    chmod +x get-modified-image.sh get-host-by-image.sh decrypt-secrets.sh && \
+RUN chmod +x get-modified-image.sh get-host-by-image.sh decrypt-secrets.sh && \
     export MODIFIED_IMAGE_FULL=$(./get-modified-image.sh) && \
     export MODIFIED_IMAGE=$(echo $MODIFIED_IMAGE_FULL | cut -d ':' -f1) && \
     export CONTAINER_NAME=$(cat $MODIFIED_IMAGE/docker-compose.yml | grep $MODIFIED_IMAGE -B1 | head -n1 | cut -d ':' -f1 | xargs) && \