Use apk's no-cache flag in Dockerfile
@@ -2,7 +2,7 @@ FROM alpine:latest
MAINTAINER Miek Gieben <miek@miek.nl> @miekg
# only need ca-certificates & openssl if want to use https_google
-RUN apk --update add bind-tools ca-certificates openssl && update-ca-certificates && rm -rf /var/cache/apk/*
+RUN apk --no-cache add bind-tools ca-certificates openssl && update-ca-certificates
ADD coredns /coredns
