ci: push Docker image to container registry

Update the CI pipeline file and Makefile to
push the Docker image on tagged releases.

Part of dananglin/pleroma-ansible-playbook#14

.gitlab-ci.yml

@@ -1,18 +1,17 @@
 ---
 stages:
 - test
+- publish
 
 .use-python:
   image: python:3.7.6-slim-buster
 
-.docker-dind-service:
+.docker-build-setup:
+  image: docker:19.03.8
   services:
   - docker:19.03.8-dind
 
-.use-docker:
-  image: docker:19.03.8
-
-.install-deps: &install-deps
+.install-make: &install-make
 - apk add --no-cache make
 
 test:dockerfile-lint:
@@ -29,11 +28,9 @@ test:dockerfile-lint:
     - master
 
 test:docker-image-build:
-  extends:
-  - .docker-dind-service
-  - .use-docker
+  extends: .docker-build-setup
   script:
-  - *install-deps
+  - *install-make
   - make image
   stage: test
   only:
@@ -61,3 +58,18 @@ test:custom-modules:
   except:
     refs:
     - master
+
+publish:docker-image:
+  extends: .docker-build-setup
+  before_script:
+  - docker login -u ${CI_REGISTRY_USER} -p ${CI_REGISTRY_PASSWORD} ${CI_REGISTRY}
+  after_script:
+  - docker logout ${CI_REGISTRY}
+  script:
+  - *install-make
+  - make publish
+  only:
+  - /^v[0-9]+(.[0-9]+){2}$/
+  variables:
+    IMAGE_NAME: ${CI_REGISTRY}/${CI_PROJECT_PATH}
+    IMAGE_TAG: ${CI_COMMIT_REF_NAME}

Makefile

@@ -5,8 +5,9 @@ PLAYBOOK_FILE ?= "playbook.yml"
 DOCKERFILE = Dockerfile
 IMAGE_NAME ?= pleroma-ansible-playbook
 IMAGE_TAG ?= latest
+DOCKER_IMAGE = $(IMAGE_NAME):$(IMAGE_TAG)
 
-PHONY: secret_key_base signing_salt vapid_private_key vapid_public_key test_modules_unit image pleroma
+PHONY: secret_key_base signing_salt vapid_private_key vapid_public_key test_modules_unit image publish pleroma
 
 all: secret_key_base signing_salt vapid_key_pair
 
@@ -35,7 +36,10 @@ test_modules_unit:
 	@find ./library -mindepth 1 -maxdepth 1 -type f -name test_*.py | xargs python3
 
 image:
-	@docker build -f $(DOCKERFILE) -t $(IMAGE_NAME):$(IMAGE_TAG) .
+	@docker build -f $(DOCKERFILE) -t $(DOCKER_IMAGE) .
+
+publish: image
+	@docker push $(DOCKER_IMAGE)
 
 pleroma:
 	ansible-playbook --inventory $(INVENTORY) --tags $(PLAYBOOK_TAGS) $(EXTRA_ARGS) $(PLAYBOOK_FILE)