proposal: unified multi-stage Dockerfile

Dockerfile

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+# Copyright AppsCode Inc. and Contributors.
+#
+# 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.
+#
+# Unified Dockerfile proposal — replaces Dockerfile.in / Dockerfile.dbg
+# / Dockerfile.ubi with a single multi-stage build selectable via
+# `docker build --target {prod|dbg|ubi}`.
+#
+# Build args (all required):
+#   BIN  — binary name (must match bin/${BIN}-${TARGETOS}-${TARGETARCH})
+#   BASE_PROD — base image for the prod target (e.g. gcr.io/distroless/...)
+#   BASE_DBG  — base image for the dbg target  (debian-based, runs dlv)
+#   BASE_UBI  — base image for the ubi target  (Red Hat UBI minimal)
+#   TAG       — release tag, only used for UBI label metadata
+#
+# Each target produces an image that contains the prebuilt binary
+# bin/${BIN}-${TARGETOS}-${TARGETARCH} (built outside this Dockerfile,
+# same as the current setup).
+
+ARG BIN
+ARG BASE_PROD
+ARG BASE_DBG
+ARG BASE_UBI
+ARG TAG=latest
+
+# ---------- prod (distroless / alpine) ----------------------------------
+FROM ${BASE_PROD} AS prod
+ARG BIN
+ARG TARGETOS
+ARG TARGETARCH
+
+LABEL org.opencontainers.image.source="https://github.com/kubeops/external-dns-operator"
+
+RUN set -x \
+  && apk add --update --upgrade --no-cache pcre2 ca-certificates tzdata \
+  && echo 'Etc/UTC' > /etc/timezone
+
+ADD bin/${BIN}-${TARGETOS}-${TARGETARCH} /${BIN}
+USER 65534
+ENTRYPOINT ["/${BIN}"]
+
+# ---------- dbg (debian + dlv) ------------------------------------------
+FROM ghcr.io/appscode/dlv:1.25 AS dlv
+
+FROM ${BASE_DBG} AS dbg
+ARG BIN
+ARG TARGETOS
+ARG TARGETARCH
+
+LABEL org.opencontainers.image.source="https://github.com/kubeops/external-dns-operator"
+
+RUN set -x \
+  && apt-get update \
+  && apt-get upgrade -y \
+  && apt-get install -y --no-install-recommends ca-certificates \
+  && rm -rf /var/lib/apt/lists/* /usr/share/doc /usr/share/man /tmp/* \
+  && echo 'Etc/UTC' > /etc/timezone
+
+ADD bin/${BIN}-${TARGETOS}-${TARGETARCH} /${BIN}
+COPY --from=dlv /usr/local/bin/dlv /bin/dlv
+
+EXPOSE 40000
+ENTRYPOINT ["/bin/dlv", "--listen=:40000", "--headless=true", "--api-version=2", "exec", "/${BIN}", "--"]
+
+# ---------- ubi (Red Hat UBI minimal) -----------------------------------
+FROM ${BASE_UBI} AS ubi
+ARG BIN
+ARG TARGETOS
+ARG TARGETARCH
+ARG TAG
+
+LABEL org.opencontainers.image.source="https://github.com/kubeops/external-dns-operator" \
+      name="External DNS Operator" \
+      maintainer=AppsCode \
+      vendor=AppsCode \
+      version=${TAG} \
+      release=${TAG} \
+      summary="External DNS Operator configures external DNS servers dynamically from Kubernetes resources" \
+      description="External DNS Operator configures external DNS servers dynamically from Kubernetes resources."
+
+RUN mkdir -p /licenses
+COPY LICENSE /licenses/
+
+RUN set -x \
+  && microdnf update -y \
+  && microdnf install -y tzdata \
+  && microdnf clean all
+
+ENV TZ=Etc/UTC
+RUN ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone
+
+ADD bin/${BIN}-${TARGETOS}-${TARGETARCH} /${BIN}
+USER 65534
+ENTRYPOINT ["/${BIN}"]