Add health check to docker container

Signed-off-by: Knut Ahlers <knut@ahlers.me>

Dockerfile

@@ -16,7 +16,7 @@ COPY --from=0 /go/bin/coredns /usr/local/bin/
 
 ADD ./requirements.txt /src/requirements.txt
 RUN set -ex \
- && apk --no-cache add python3 \
+ && apk --no-cache add python3 bind-tools \
  && pip3 install -r /src/requirements.txt
 
 ADD . /src
@@ -26,5 +26,8 @@ EXPOSE 53/udp 53
 
 VOLUME ["/src/zones"]
 
+HEALTHCHECK --interval=30s --timeout=5s \
+  CMD dig +short @localhost health.server.test TXT || exit 1
+
 ENTRYPOINT ["/usr/local/bin/coredns"]
 CMD ["--"]

zones.yml

@@ -354,4 +354,10 @@ zones:
       - name: ""
         alias: docker01.cloud.kserver.biz.
 
+  server.test:
+    entries:
+      - name: health
+        type: TXT
+        records:
+          - "OK"
 ...