Add DNS lookup plugin

config/network-problem-monitor.json

@@ -15,6 +15,12 @@
       "reason": "ConntrackFull",
       "path": "./config/plugin/network_problem.sh",
       "timeout": "3s"
+    },
+    {
+      "type": "temporary",
+      "reason": "DNSUnreachable",
+      "path": "./config/plugin/dns_problem.sh",
+      "timeout": "3s"
     }
   ]
 }

config/plugin/dns_problem.sh

@@ -0,0 +1,24 @@
+#!/bin/bash
+
+# This plugin checks for dns network issues.
+
+readonly OK=0
+readonly NONOK=1
+readonly UNKNOWN=2
+
+readonly KUBERNETES_SERVICE='kubernetes.default'
+
+# Check getent command is present
+if ! command -v getent >/dev/null; then
+  echo "Could not find 'getent' - require getent"
+  exit $UNKNOWN
+fi
+
+# Return success if a DNS lookup to the Kubernetes host is successful
+if getent hosts "${KUBERNETES_SERVICE}" >/dev/null; then
+  echo "DNS lookup to ${KUBERNETES_SERVICE} is working"
+  exit $OK
+else
+  echo "DNS lookup to ${KUBERNETES_SERVICE} is not working"
+  exit $NONOK
+fi