interop/xds: dockerfile for the xds interop client

interop/xds/client/Dockerfile

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+# Copyright 2021 gRPC authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Dockerfile for building the xDS interop client. To build the image, run the
+# following command from grpc-go directory:
+# docker build -t <TAG> -f interop/xds/client/Dockerfile .
+
+FROM golang:1.16-alpine as build
+
+# Make a grpc-go directory and copy the repo into it.
+WORKDIR /go/src/grpc-go
+COPY . .
+
+# Build a static binary without cgo so that we can copy just the binary in the
+# final image, and can get rid of Go compiler and gRPC-Go dependencies.
+RUN go build -tags osusergo,netgo interop/xds/client/client.go
+
+# Second stage of the build which copies over only the client binary and skips
+# the Go compiler and gRPC repo from the earlier stage. This significantly
+# reduces the docker image size.
+FROM alpine
+COPY --from=build /go/src/grpc-go/client .
+ENTRYPOINT ["./client"]