Fix travis docker image pulling for docs

.travis.yml

@@ -16,7 +16,7 @@ env:
 
 script:
 - echo "Skipping tests... (Tests are executed on SemaphoreCI)"
-- if [ "$TRAVIS_PULL_REQUEST" != "false" ]; then make docs; fi
+- if [ "$TRAVIS_PULL_REQUEST" != "false" ]; then travis_retry make docs-pull-images && make docs; fi
 
 before_deploy:
   - >

Makefile

@@ -127,6 +127,10 @@ docs:
 docs-serve:
 	make -C ./docs docs-serve
 
+## Pull image for doc building
+docs-pull-images:
+	make -C ./docs docs-pull-images
+
 ## Generate CRD clientset
 generate-crd:
 	./script/update-generated-crd-code.sh

docs/Makefile

@@ -22,6 +22,10 @@ docs: docs-clean docs-image docs-lint docs-build docs-verify
 docs-serve: docs-image
 	docker run  $(DOCKER_RUN_DOC_OPTS) $(TRAEFIK_DOCS_BUILD_IMAGE) mkdocs serve
 
+## Pull image for doc building
+docs-pull-images:
+	grep --no-filename -E '^FROM' ./*.Dockerfile | awk '{print $$2}' | sort | uniq | xargs -P 6 -n 1 docker pull
+
 # Utilities Targets for each step
 docs-image:
 	docker build -t $(TRAEFIK_DOCS_BUILD_IMAGE) -f docs.Dockerfile ./