Implement multi-stage pattern to reduce docker image from 800mb to 7mb

Dockerfile

@@ -1,10 +1,31 @@
-FROM golang:1.9.3
+FROM golang:alpine as builder
 
-RUN mkdir -p /go/src/baton
+# get deps ca-certs and git
-WORKDIR /go/src/baton
+RUN apk update && apk add git && apk add ca-certificates
+ADD https://github.com/golang/dep/releases/download/v0.4.1/dep-linux-amd64 /usr/bin/dep
+RUN chmod +x /usr/bin/dep
 
-COPY . .
+# create baton user
+RUN adduser -D -g '' batonuser
 
-RUN go install
+# copy src and set working directory
+COPY . $GOPATH/src/baton/
+WORKDIR $GOPATH/src/baton/
 
-ENTRYPOINT ["baton"]
+# run dep 
+RUN dep ensure --vendor-only
+
+# disable support for c system libs, for use with scratch
+ENV CGO_ENABLED 0
+ENV GOOS linux
+ENV GOARCH amd64
+
+# build and test our binary
+RUN go test -v
+RUN go build -a -installsuffix cgo -o /go/bin/baton
+
+FROM scratch
+COPY --from=builder /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
+COPY --from=builder /etc/passwd /etc/passwd
+COPY --from=builder /go/bin/baton /go/bin/baton
+ENTRYPOINT ["/go/bin/baton"]