chore: support multi-container Dockerfile multiple architecture

Signed-off-by: kahirokunn <okinakahiro@gmail.com>

code-samples/serving/multi-container/README.md

@@ -68,6 +68,10 @@ You can do this by copying the following code into the `servingcontainer.go` fil
    # This is based on Debian and sets the GOPATH to /go.
    # https://hub.docker.com/_/golang
    FROM golang:1.15 as builder
+
+   ARG TARGETOS
+   ARG TARGETARCH
+
    # Create and change to the app directory.
    WORKDIR /app
    # Retrieve application dependencies using go modules.
@@ -78,7 +82,7 @@ You can do this by copying the following code into the `servingcontainer.go` fil
    COPY . ./
    # Build the binary.
    # -mod=readonly ensures immutable go.mod and go.sum in container builds.
-   RUN CGO_ENABLED=0 GOOS=linux go build -mod=readonly -v -o servingcontainer
+   RUN CGO_ENABLED=0 GOOS=linux GOOS=${TARGETOS} GOARCH=${TARGETARCH} go build -mod=readonly -v -o servingcontainer
    # Use the official Alpine image for a lean production container.
    # https://hub.docker.com/_/alpine
    # https://docs.docker.com/develop/develop-images/multistage-build/#use-multi-stage-builds
@@ -125,6 +129,10 @@ You can do this by copying the following code into the `sidecarcontainer.go` fil
    # This is based on Debian and sets the GOPATH to /go.
    # https://hub.docker.com/_/golang
    FROM golang:1.15 as builder
+
+   ARG TARGETOS
+   ARG TARGETARCH
+
    # Create and change to the app directory.
    WORKDIR /app
    # Retrieve application dependencies using go modules.
@@ -135,7 +143,7 @@ You can do this by copying the following code into the `sidecarcontainer.go` fil
    COPY . ./
    # Build the binary.
    # -mod=readonly ensures immutable go.mod and go.sum in container builds.
-   RUN CGO_ENABLED=0 GOOS=linux go build -mod=readonly -v -o sidecarcontainer
+   RUN CGO_ENABLED=0 GOOS=linux GOOS=${TARGETOS} GOARCH=${TARGETARCH} go build -mod=readonly -v -o sidecarcontainer
    # Use the official Alpine image for a lean production container.
    # https://hub.docker.com/_/alpine
    # https://docs.docker.com/develop/develop-images/multistage-build/#use-multi-stage-builds