Use the czin/knots image as base (uses Alpine Linux).

.dockerignore

+.git/
+README*
+*.swp

Dockerfile

-FROM debian:stretch-slim
-ENV DEBIAN_FRONTEND noninteractive
-RUN apt-get update && \
-    apt-get install -y knot-dnsutils knot-host knot-resolver dma bsd-mailx && \
-    rm -rf /tmp/* /var/tmp/* /var/lib/apt/lists/* /var/cache/apt/archives/*
-COPY entrypoint.sh /entrypoint.sh
-ENTRYPOINT ["/entrypoint.sh"]
-CMD ["/bin/bash", "--login"]
+FROM cznic/knot-resolver
+RUN echo '@testing http://dl-cdn.alpinelinux.org/alpine/edge/testing' >> /etc/apk/repositories && \
+    apk add --update \
+        dma@testing \
+        iproute2 \
+        knot-utils \
+        mailx \
+        mtr \
+    && \
+    rm -rf /var/cache/apk/* /tmp/* /var/tmp/*
+COPY entrypoint /entrypoint
+ENTRYPOINT [ "/entrypoint" ]
+CMD [ "bash", "--login" ]

README.md

@@ -5,5 +5,4 @@ https://www.shore.co.il/blog/resolver/.
 
 ## Usage
 
-    docker pull adarnimrod/resolver
     docker run -it adarnimrod/resolver

entrypoint.sh → entrypoint

 #!/bin/sh
 set -eu
-service kresd start
+echo "net = { '127.0.0.1', '::1'}" | nohup kresd -f1 &
 echo 'nameserver 127.0.0.1' > /etc/resolv.conf
 eval "exec $@"