Use 'setcap' to bind to port 53 in the container

Dockerfile

@@ -22,15 +22,20 @@ RUN echo "replace github.com/btcsuite/btcd => github.com/gtank/btcd v0.0.0-20191
 RUN make all \
 	&& mv coredns /usr/bin/coredns
 
+
 FROM alpine:latest
 
+RUN apk --no-cache add libcap
+
 COPY --from=builder /usr/bin/coredns /usr/bin/coredns
 COPY --from=builder /etc/ssl/certs/ /etc/ssl/certs
 
 COPY coredns/Corefile /etc/dnsseeder/Corefile
 
-# DNS will bind to 8053
-EXPOSE 8053
+RUN setcap 'cap_net_bind_service=+ep' /usr/bin/coredns
+
+# DNS will bind to 53
+EXPOSE 53
 
 # Global health check will respond 200 OK on 8080
 EXPOSE 8080
@@ -41,4 +46,4 @@ RUN adduser --disabled-password dnsseeder
 USER dnsseeder
 
 ENTRYPOINT [ "coredns" ]
-CMD [ "-conf", "/etc/dnsseeder/Corefile", "-dns.port", "8053"]
+CMD [ "-conf", "/etc/dnsseeder/Corefile"]

Makefile

@@ -1,6 +1,6 @@
 .PHONY: docker docker-run docker-clean install uninstall all clean
 
-VERSION=v0.1.0
+VERSION=v0.1.1
 
 all: build_output/coredns
 
@@ -23,7 +23,7 @@ docker:
 	docker build -t zfnd-seeder:$(VERSION) -f Dockerfile .
 
 docker-run:
-	docker run -d --rm -p 1053:8053/udp -p 1053:8053/tcp -p 8080 zfnd-seeder:$(VERSION)
+	docker run -d --rm -p 1053:53/udp -p 1053:53/tcp -p 8080 zfnd-seeder:$(VERSION)
 
 docker-clean:
 	docker rmi zfnd-seeder:$(VERSION)