Add .gitlab-ci.yml to build Dockerfile with cache for master, tag, and all.

.gitlab-ci.yml

@@ -0,0 +1,40 @@
+image: docker:latest
+
+services:
+  - docker:dind
+
+before_script:
+  - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
+
+build-master:
+  stage: build
+  script:
+    - docker pull "$CI_REGISTRY_IMAGE:latest" || true
+    - docker build --cache-from "$CI_REGISTRY_IMAGE:latest" --pull -t "$CI_REGISTRY_IMAGE:latest" .
+    - docker push "$CI_REGISTRY_IMAGE:latest"
+  only:
+    - master
+    - schedules
+
+build-master-tag:
+  stage: build
+  script:
+    - docker build --pull -t $CI_REGISTRY_IMAGE:$CI_COMMIT_TAG .
+    - docker push $CI_REGISTRY_IMAGE:$CI_COMMIT_TAG
+  only:
+    - tags
+    - schedules
+    - master
+  except:
+    - branches
+
+build:
+  stage: build
+  script:
+    - docker pull "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG" || true
+    - docker build --cache-from "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG" --pull -t "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG" .
+    - docker push "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG"
+  except:
+    - master
+  only:
+    - branches