split the dockerfile (#104)

Dockerfile

@@ -1,25 +1,24 @@
-# Build docker image at gcr.io/images-public/metadata:<tag>
+# This file builds the metadata backend server image at
+# gcr.io/kubeflow-images-public/metadata.
+#
+# The docker build flags are
+# BASE_IMG: base image that has Go and Bazel installed.
+# OUTPUT_DIR: the platform name that Bazel used to ouput the executable.
 
-FROM golang:1.12
+ARG BASE_IMG=gcr.io/kubeflow-images-public/metadata-base
+FROM ${BASE_IMG}
 
-ENV GO111MODULE on
-
-RUN apt-get update && apt-get -y install cmake unzip patch wget && apt-get clean
+ARG OUTPUT_DIR=linux_amd64_stripped
 
-RUN cd /tmp && \
-    wget -O /tmp/bazel-installer.sh https://github.com/bazelbuild/bazel/releases/download/0.24.1/bazel-0.24.1-installer-linux-x86_64.sh && \
-    chmod +x bazel-installer.sh && \
-    ./bazel-installer.sh --user
-
-ENV PATH=/root/bin:${PATH}
+ENV GO111MODULE on
 
 WORKDIR /go/src/github.com/kubeflow/metadata
 
 COPY . .
 
 RUN bazel build -c opt --define=grpc_no_ares=true //...
 
-RUN cp bazel-bin/server/linux_amd64_stripped/server server/server
+RUN cp bazel-bin/server/${OUTPUT_DIR}/server server/server
 
 # Copy Licenses
 RUN wget https://github.com/grpc-ecosystem/grpc-gateway/blob/master/LICENSE.txt -O GRPC-GATEWAY-LICENSE.txt

dockerfiles/Dockerfile-linux-base

@@ -0,0 +1,15 @@
+# This file builds the base image for metadata backend server.
+# The images are at gcr.io/kubeflow-images-public/metadata-base.
+
+FROM golang:1.12
+
+RUN apt-get update && apt-get -y install cmake unzip patch wget && apt-get clean
+
+RUN cd /tmp && \
+    wget -O /tmp/bazel-installer.sh https://github.com/bazelbuild/bazel/releases/download/0.24.1/bazel-0.24.1-installer-linux-x86_64.sh && \
+    chmod +x bazel-installer.sh && \
+    ./bazel-installer.sh --user
+
+ENV PATH=/root/bin:${PATH}
+
+CMD ["bash"]