Apply cap_net_bind_service to kube-apiserver binary.

build/server-image/kube-apiserver/Dockerfile

@@ -0,0 +1,27 @@
+# Copyright 2021 The Kubernetes 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.
+
+# This file create the kube-apiserver image.
+ARG BASEIMAGE
+
+FROM k8s.gcr.io/build-image/setcap:buster-v1.4.0
+ARG BINARY
+COPY ${BINARY} /${BINARY}
+# We apply cap_net_bind_service so that kube-apiserver can be run as
+# non-root and still listen on port less than 1024
+RUN setcap cap_net_bind_service=+ep /${BINARY}
+
+FROM ${BASEIMAGE}
+ARG BINARY
+COPY --from=0 /${BINARY} /usr/local/bin/${BINARY}