Dockerfile upgrade for multi target

Dockerfile

@@ -1,46 +1,60 @@
+# -------------------- deps stage --------------------
 FROM golang:alpine AS deps
 
 WORKDIR /app
 COPY go.mod go.sum ./
-RUN sed -i '/replace/d' go.mod
-RUN go mod download
+RUN sed -i '/replace/d' go.mod && \
+    go mod download
 
-#----------------------------------------------------------------------------------------------
+# -------------------- builder stage --------------------
+FROM --platform=$BUILDPLATFORM golang:alpine AS builder
 
-FROM golang:alpine AS builder
+# Buildx injects these
+ARG TARGETOS
+ARG TARGETARCH
+
+# We want static binaries for scratch
+ENV CGO_ENABLED=0
 
 WORKDIR /app
 
-RUN apk add git
+# tools needed during build
+RUN apk add --no-cache git
 
+# install bee for the BUILD platform 
 RUN go install github.com/beego/bee/v2@latest
 
 WORKDIR /oc-discovery
 
+# reuse module cache from deps
 COPY --from=deps /go/pkg /go/pkg
 COPY --from=deps /app/go.mod /app/go.sum ./
 
-RUN export CGO_ENABLED=0 && \
-    export GOOS=linux && \
-    export GOARCH=amd64 && \
-    export BUILD_FLAGS="-ldflags='-w -s'"
-
+# copy the source code
 COPY . .
 
 RUN sed -i '/replace/d' go.mod
-RUN bee pack
-RUN mkdir -p /app/extracted && tar -zxvf oc-discovery.tar.gz -C /app/extracted
-#RUN sed -i 's/http:\/\/127.0.0.1:8080\/swagger\/swagger.json/swagger.json/g' /app/extracted/swagger/index.html
 
-#----------------------------------------------------------------------------------------------
+# build
+RUN GOOS=$TARGETOS GOARCH=$TARGETARCH CGO_ENABLED=0 bee pack
 
-FROM golang:alpine
+# unpack bee's tarball
+RUN mkdir -p /app/extracted && \
+    tar -zxvf oc-discovery.tar.gz -C /app/extracted && \
+    sed -i 's#http://127.0.0.1:8080/swagger/swagger.json#swagger.json#g' \
+      /app/extracted/swagger/index.html
+
+# -------------------- final image --------------------
+FROM scratch
 
 WORKDIR /app
-COPY --from=builder /app/extracted/oc-discovery /usr/bin/ 
-#COPY --from=builder /app/extracted/swagger /app/swagger
+
+# copy the binary & assets
+COPY --from=builder /app/extracted/oc-discovery /usr/bin/oc-discovery
+COPY --from=builder /app/extracted/swagger ./swagger
 COPY --from=builder /app/extracted/docker_discovery.json /etc/oc/discovery.json
 
 EXPOSE 8080
 
-ENTRYPOINT ["oc-discovery"]
+# run
+ENTRYPOINT ["/usr/bin/oc-discovery"]