Optimize docker build

Dockerfile

@@ -1,18 +1,28 @@
 ARG GO_VERSION
 ARG ALPINE_VERSION
 
+# buildkit
+ARG TARGETOS="linux"
+ARG TARGETARCH="amd64"
 ARG BUILDPLATFORM="linux/amd64"
-ARG GO_SOCKADDR_VERSION="master"
 
-FROM golang:${GO_VERSION}-alpine${ALPINE_VERSION} AS builder
+FROM --platform=${BUILDPLATFORM} golang:${GO_VERSION}-alpine${ALPINE_VERSION} AS builder
 RUN apk add --no-cache git make
-ARG GO_SOCKADDR_VERSION
-ADD https://github.com/hashicorp/go-discover.git#${GO_SOCKADDR_VERSION} /hashicorp/go-discover
-RUN <<EOT
+ARG GO_SOCKADDR_VERSION="master"
+ADD https://github.com/hashicorp/go-discover.git#${GO_SOCKADDR_VERSION} /tmp/source
+RUN --mount=type=cache,target=/go/pkg/mod \
+    <<EOT
     set -ex
-    cd /hashicorp/go-discover/cmd/discover
-    go build -o /discover
+    cd /tmp/source/cmd/discover
+    export CGO_ENABLED=0
+    export GOOS=linux
+    for GOARCH in amd64 arm64; do
+        export GOARCH
+        go build -o /discover-$GOOS-$GOARCH
+    done
 EOT
 
 FROM scratch
-COPY --from=builder /hashicorp/go-discover/cmd/discover /discover
+ARG TARGETOS
+ARG TARGETARCH
+COPY --from=builder /discover-$TARGETOS-$TARGETARCH /discover