optimize dockerfile caching for go builds

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>

src/checkoutservice/Dockerfile

@@ -1,7 +1,14 @@
 FROM golang:1.10-alpine as builder
 RUN apk add --no-cache ca-certificates git
 WORKDIR /go/src/checkoutservice
+
+# get known dependencies
+RUN go get -d github.com/google/uuid \
+    google.golang.org/grpc \
+    google.golang.org/grpc/codes \
+    google.golang.org/grpc/status
 COPY . .
+# get remaining dependencies
 RUN go get -d ./...
 RUN go build -o /checkoutservice .
 

src/productcatalogservice/Dockerfile

@@ -3,7 +3,13 @@ RUN apk add --no-cache \
   ca-certificates \
   git
 WORKDIR /src/microservices-demo/productcatalogservice
+# get known dependencies
+RUN go get -d google.golang.org/grpc \
+    google.golang.org/grpc/codes \
+    google.golang.org/grpc/status
+
 COPY . .
+# get remaining dependencies
 RUN go get -d ./...
 RUN go build -o /productcatalogservice .
 

src/shippingservice/Dockerfile

@@ -3,7 +3,12 @@ RUN apk add --no-cache \
   ca-certificates \
   git
 WORKDIR /src/microservices-demo/shippingservice
+# get known dependencies
+RUN go get -d golang.org/x/net/context \
+google.golang.org/grpc \
+google.golang.org/grpc/reflection
 COPY . .
+# get other dependencies
 RUN go get -d ./...
 RUN go build -o /shippingservice .