gitlab docker build

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diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
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+# This is a GitLab CI configuration to build the project as a docker image
+# The file is generic enough to be dropped in a project containing a working Dockerfile
+# Author: Florent CHAUVEAU <florent.chauveau@gmail.com>
+# Mentioned here: https://blog.callr.tech/building-docker-images-with-gitlab-ci-best-practices/
+
+# do not use "latest" here, if you want this to work in the future
+image: docker:18
+
+stages:
+  - build
+  - push
+
+# Use this if your GitLab runner does not use socket binding
+services:
+  - docker:dind
+
+before_script:
+  # docker login asks for the password to be passed through stdin for security
+  # we use $CI_JOB_TOKEN here which is a special token provided by GitLab
+  - echo -n $CI_JOB_TOKEN | docker login -u gitlab-ci-token --password-stdin $CI_REGISTRY
+
+Build:
+  stage: build
+  script:
+    # fetches the latest image (not failing if image is not found)
+    - docker pull $CI_REGISTRY_IMAGE:latest || true
+    # builds the project, passing proxy variables, and vcs vars for LABEL
+    # notice the cache-from, which is going to use the image we just pulled locally
+    # the built image is tagged locally with the commit SHA, and then pushed to 
+    # the GitLab registry
+    - >
+      docker build
+      --pull
+      --build-arg VCS_REF=$CI_COMMIT_SHA
+      --build-arg VCS_URL=$CI_PROJECT_URL
+      --cache-from $CI_REGISTRY_IMAGE:latest
+      --tag $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
+      .
+    - docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
+
+# Here, the goal is to tag the "master" branch as "latest"
+Push latest:
+  variables:
+    # We are just playing with Docker here. 
+    # We do not need GitLab to clone the source code.
+    GIT_STRATEGY: none
+  stage: push
+  only:
+    # Only "master" should be tagged "latest"
+    - master
+  script:
+    # Because we have no guarantee that this job will be picked up by the same runner 
+    # that built the image in the previous step, we pull it again locally
+    - docker pull $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
+    # Then we tag it "latest"
+    - docker tag $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA $CI_REGISTRY_IMAGE:latest
+    # Annnd we push it.
+    - docker push $CI_REGISTRY_IMAGE:latest
+
+# Finally, the goal here is to Docker tag any Git tag
+# GitLab will start a new pipeline everytime a Git tag is created, which is pretty awesome
+Push tag:
+  variables:
+    # Again, we do not need the source code here. Just playing with Docker.
+    GIT_STRATEGY: none
+  stage: push
+  only:
+    # We want this job to be run on tags only.
+    - tags
+  script:
+    - docker pull $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA
+    - docker tag $CI_REGISTRY_IMAGE:$CI_COMMIT_SHA $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_NAME
+    - docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_REF_NAME