Add a liveness probe to the DNS container.

cluster/addons/dns/skydns-rc.yaml.in

@@ -48,6 +48,17 @@ spec:
         - containerPort: 53
           name: dns
           protocol: UDP
+        livenessProbe:
+          exec:
+            command:
+            - "/bin/sh"
+            - "-c"
+            # The health check succeeds by virtue of not hanging. It'd be nice
+            # to also check local services are known, but if that's broken then
+            # etcd or kube2sky has to be restarted, not skydns.
+            - "nslookup foobar 127.0.0.1 &> /dev/null; echo ok"
+          initialDelaySeconds: 30
+          timeoutSeconds: 5
       dnsPolicy: Default  # Don't use cluster DNS.
       volumes:
       - name: dns-token