Simplify how the docker image is built

Dockerfile

@@ -1,8 +1,27 @@
+# build stage
+FROM golang:1.11.1-alpine AS build-env
+
+ENV GOPATH /go
+ENV GOOS linux
+
+RUN apk add --update git bash
+
+ADD packaging/install-vips.sh install-vips.sh
+RUN ./install-vips.sh
+
+ADD . /go/src/github.com/zalando-stups/skrop
+WORKDIR /go/src/github.com/zalando-stups/skrop
+
+RUN go get github.com/Masterminds/glide
+
+RUN go build ./cmd/skrop
+
+# final stage
 FROM danpersa/alpine-mozjpeg-vips:3.3.1-8.7.0
 
 ARG ROUTES_FILE
 
-ADD skrop /usr/local/bin/
+COPY --from=0 /go/src/github.com/zalando-stups/skrop/skrop /usr/local/bin/
 ADD $ROUTES_FILE skrop.eskip
 
 ENTRYPOINT skrop -routes-file skrop.eskip ${SKROP_ARGS}

packaging/build.sh

@@ -6,45 +6,13 @@ readonly DOCKER_IMAGE_NAME=${3-"zalando-stups/skrop"}
 
 readonly GO_PROJECT_NAME="github.com/zalando-stups/skrop"
 
-function make_build_image() {
-  docker build -t "$DOCKER_IMAGE_NAME-build" packaging/ \
-  && return 0
-}
-
-function make_binary() {
-  docker run --rm \
-    -v ${PWD}:/go/src/${GO_PROJECT_NAME} \
-    -e "GOPATH=/go" \
-    -e "GOOS=linux" \
-    -w /go/src/${GO_PROJECT_NAME} \
-    "$DOCKER_IMAGE_NAME-build" sh \
-    -c 'go build ./cmd/skrop' \
-  && return 0
-}
-
 function make_production_image() {
   docker build \
   --build-arg ROUTES_FILE=${ROUTES_FILE} \
   -t ${DOCKER_IMAGE_NAME}:${DOCKER_IMAGE_VERSION} . \
   && return 0
 }
 
-echo >&2 "Building build Docker image…"
-
-make_build_image
-if [ "$?" -ne 0 ]; then
-  echo >&2 "Aborting!"
-  exit 1
-fi
-
-echo >&2 "Building binary…"
-
-make_binary
-if [ "$?" -ne 0 ]; then
-  echo >&2 "Aborting!"
-  exit 1
-fi
-
 echo >&2 "Building Docker image…"
 
 make_production_image