ipabusedb-docker-reporter: build and push multi-arch image

make push builds linux/amd64 and linux/arm64 natively, each on a daemon
of that arch (amd64 on fsn1app1 via DOCKER_HOST, arm64 locally), pushes
the per-arch tags, and joins them into the dated and latest manifest
lists with docker buildx imagetools, mirroring the baseimage repo.

ipabusedb-docker-reporter/Makefile

@@ -2,17 +2,39 @@ BIN := ipabusedb-docker-reporter
 IMAGE := git.eeqj.de/sneak/$(BIN)
 TAG := $(shell date -u +%Y-%m-%d)
 
-.PHONY: build test lint fmt fmt-check check clean image push
+# Each arch is built natively on a daemon of that arch: arm64 on the local
+# daemon, amd64 on fsn1app1. Override on the command line if needed.
+ARCHES := amd64 arm64
+DOCKER_HOST_amd64 ?= ssh://root@fsn1app1
+DOCKER_HOST_arm64 ?=
+docker_for = $(if $(DOCKER_HOST_$(1)),DOCKER_HOST=$(DOCKER_HOST_$(1))) docker
+
+.PHONY: build test lint fmt fmt-check check clean image push manifest \
+	$(ARCHES:%=image-%) $(ARCHES:%=push-%)
 
 build:
 	go build -o $(BIN) .
 
+# Local image for this machine's arch, for testing.
 image:
-	docker build -t $(BIN) -t $(IMAGE):$(TAG) -t $(IMAGE):latest .
+	docker build -t $(BIN) .
 
-push: image
-	docker push $(IMAGE):$(TAG)
-	docker push $(IMAGE):latest
+# image-ARCH builds on that arch's daemon; push-ARCH pushes the arch tag.
+define arch_rules
+image-$(1):
+	$$(call docker_for,$(1)) build --platform linux/$(1) -t $$(IMAGE):$(1) .
+
+push-$(1): image-$(1)
+	$$(call docker_for,$(1)) push $$(IMAGE):$(1)
+endef
+$(foreach a,$(ARCHES),$(eval $(call arch_rules,$(a))))
+
+# Join the per-arch tags into the dated and latest multi-arch manifests.
+manifest:
+	docker buildx imagetools create -t $(IMAGE):$(TAG) -t $(IMAGE):latest \
+		$(ARCHES:%=$(IMAGE):%)
+
+push: $(ARCHES:%=push-%) manifest
 
 test:
 	go test ./...