Docker: drop alpine
* Docker: drop alpine
Create a multistage docker build image that uses debian to install certs
and then create the final image by using FROM: scratch. This creates a
(slightly) smaller images and drops busybox and alpine.
* Even less copying
-FROM alpine:latest
+FROM debian:stable-slim
-# Only need ca-certificates & openssl if want to use DNS over TLS (RFC 7858).
-RUN apk --no-cache add bind-tools ca-certificates openssl && update-ca-certificates
+RUN apt-get update && apt-get -uy upgrade
+RUN apt-get -y install ca-certificates && update-ca-certificates
+FROM scratch
+
+COPY --from=0 /etc/ssl/certs /etc/ssl/certs
ADD coredns /coredns
EXPOSE 53 53/udp
