Add DOCKER_BUILDX to inject path of buildx binary

Signed-off-by: Davanum Srinivas <davanum@gmail.com>

Makefile

@@ -14,6 +14,9 @@ CONTAINER_RUN     = "$(CONTAINER_ENGINE)" run --rm --interactive --tty --volume
 CCRED=\033[0;31m
 CCEND=\033[0m
 
+# Docker buildx related settings for multi-arch images
+DOCKER_BUILDX ?= docker buildx
+
 .PHONY: all build build-preview help serve
 
 help: ## Show this help.
@@ -78,17 +81,17 @@ PLATFORMS ?= linux/arm64,linux/amd64
 docker-push: ## Build a multi-architecture image and push that into the registry
 	docker run --rm --privileged tonistiigi/binfmt:qemu-v6.2.0-26@sha256:5bf63a53ad6222538112b5ced0f1afb8509132773ea6dd3991a197464962854e --install all
 	docker version
-	docker buildx version
-	docker buildx create --use --name=image-builder 2>/dev/null || docker buildx use --default image-builder
-	# copy existing Dockerfile and insert --platform=${BUILDPLATFORM} into Dockerfile.cross, and preserve the original Dockerfile
-	sed -e '1 s/\(^FROM\)/FROM --platform=\$$\{BUILDPLATFORM\}/; t' -e ' 1,// s//FROM --platform=\$$\{BUILDPLATFORM\}/' Dockerfile > Dockerfile.cross
-	docker buildx build \
+	$(DOCKER_BUILDX) version
+	$(DOCKER_BUILDX) inspect image-builder > /dev/null 2>&1 || $(DOCKER_BUILDX) create --name image-builder --use
+	# copy existing Dockerfile and insert --platform=${TARGETPLATFORM} into Dockerfile.cross, and preserve the original Dockerfile
+	sed -e 's/\(^FROM\)/FROM --platform=\$$\{TARGETPLATFORM\}/' Dockerfile > Dockerfile.cross
+	$(DOCKER_BUILDX) build \
 		--push \
 		--platform=$(PLATFORMS) \
 		--build-arg HUGO_VERSION=$(HUGO_VERSION) \
 		--tag $(CONTAINER_IMAGE) \
 		-f Dockerfile.cross .
-	docker buildx stop image-builder
+	$(DOCKER_BUILDX) stop image-builder
 	rm Dockerfile.cross
 
 container-build: module-check

cloudbuild.yaml

@@ -20,7 +20,8 @@ steps:
       - -c
       - |
         gcloud auth configure-docker \
-        && make container-push
+        && apk add sed \
+        && make docker-push
 substitutions:
   # _GIT_TAG will be filled with a git-based tag for the image, of the form vYYYYMMDD-hash, and
   # can be used as a substitution