Use tonistiigi/xx for cross-platform builds

Update the Dockerfile to use tonistiigi/xx to cross-compile the
manager binaries natively and speed up the multi-arch image build
time.

Signed-off-by: Sunny <darkowlzz@protonmail.com>

Dockerfile

@@ -1,4 +1,13 @@
-FROM golang:1.16-alpine as builder
+ARG XX_VERSION=1.0.0-rc.2
+
+FROM --platform=$BUILDPLATFORM tonistiigi/xx:${XX_VERSION} AS xx
+
+FROM --platform=$BUILDPLATFORM golang:1.16-alpine as builder
+
+# Copy the build utilities.
+COPY --from=xx / /
+
+ARG TARGETPLATFORM
 
 WORKDIR /workspace
 
@@ -18,7 +27,8 @@ COPY controllers/ controllers/
 COPY internal/ internal/
 
 # build
-RUN CGO_ENABLED=0 go build -a -o notification-controller main.go
+ENV CGO_ENABLED=0
+RUN xx-go build -a -o notification-controller main.go
 
 FROM alpine:3.13
 

Makefile

@@ -10,6 +10,11 @@ else
 GOBIN=$(shell go env GOBIN)
 endif
 
+# Allows for defining additional Docker buildx arguments, e.g. '--push'.
+BUILD_ARGS ?=
+# Architectures to build images for.
+BUILD_PLATFORMS ?= linux/amd64
+
 all: manager
 
 # Run tests
@@ -82,7 +87,11 @@ generate: controller-gen
 
 # Build the docker image
 docker-build: test
-	docker build . -t ${IMG}
+	docker buildx build \
+	--platform=$(BUILD_PLATFORMS) \
+	-t ${IMG} \
+	--load \
+	${BUILD_ARGS} .
 
 # Push the docker image
 docker-push: