Update .gitlab-ci.yml

.gitlab-ci.yml

@@ -1,11 +1,21 @@
-build-docker:
-    image: docker:cli
-    before_script:
-        - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
-    script:
-        - docker build --pull -t illegitimate:$CI_COMMIT_BRANCH .
-        - docker push "illegitimate:$CI_COMMIT_BRANCH"
-    rules:
+docker-build:
+  image: docker:cli
+  stage: build
+  services:
+    - docker:dind
+  variables:
+    DOCKER_IMAGE_NAME: illegitimate:$CI_COMMIT_REF_SLUG
+  before_script:
+    - docker login -u "$CI_REGISTRY_USER" -p "$CI_REGISTRY_PASSWORD" $CI_REGISTRY
+  script:
+    - docker build --pull -t "$DOCKER_IMAGE_NAME" .
+    - docker push "$DOCKER_IMAGE_NAME"
+    - |
+      if [[ "$CI_COMMIT_BRANCH" == "$CI_DEFAULT_BRANCH" ]]; then
+        docker tag "$DOCKER_IMAGE_NAME" "$CI_REGISTRY_IMAGE:latest"
+        docker push "$CI_REGISTRY_IMAGE:latest"
+      fi
+  rules:
     - if: $CI_COMMIT_BRANCH
       exists:
         - Dockerfile