Add custom build of coredns

Dockerfile

@@ -0,0 +1,20 @@
+FROM golang:alpine
+
+ADD ./build.sh /usr/local/bin/build.sh
+RUN set -ex \
+ && apk --no-cache add git bash \
+ && bash /usr/local/bin/build.sh
+
+FROM alpine
+
+LABEL maintainer Knut Ahlers <knut@ahlers.me>
+
+COPY --from=0 /go/bin/coredns /usr/local/bin/
+
+ADD . /src
+WORKDIR /src
+
+EXPOSE 53/udp
+
+ENTRYPOINT ["/usr/local/bin/coredns"]
+CMD ["--"]

build.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+set -euxo pipefail
+
+IFS=$'\n'
+
+GOPKGS=(
+  'github.com/coredns/coredns'
+  'github.com/Luzifer/alias'
+)
+
+for pkg in ${GOPKGS[@]}; do
+  go get -d -v "${pkg}"
+done
+
+PLUGINS=(
+  '/^file:file/ i alias:github.com/Luzifer/alias'
+)
+
+cd /go/src/github.com/coredns/coredns
+for insert in ${PLUGINS[@]}; do
+  sed -i "${insert}" plugin.cfg
+done
+
+go generate
+go install