title: Kafka monitoring in cluster environment
body: <p>I have an kafka cluster (3 machine with 1 zookeeper and 1 broker run on each machine)
  I am using kafka_exporter to monitoring consumer lag metric, it's work fine in normal case.
  But, when i kill 1 broker, the Prometheus cannot get metric from <a href="http://machine1:9308/metric" rel="nofollow noreferrer">http://machine1:9308/metric</a> (kafka_exporter metric endpoint), because it take a long time to get data (1,5m), so it will be timeout.
  Now, if I restart kafka_exporter I will see some error:</p>
  
  <pre><code>Cannot get leader of topic __consumer_offsets partition 20: kafka server: In the middle of a leadership election, there is currently no leader for this partition and hence it is unavailable for writes
  </code></pre>
  
  <p>When I run the command: kafka-topics.bat --describe --zookeeper machine1:2181,machine2:2181,machine3:2181 --topic __consumer_offsets
  The result are:</p>
  
  <pre><code>Topic:__consumer_offsets        PartitionCount:50       ReplicationFactor:1     Configs:compression.type=producer,cleanup.policy=compact,segment.bytes=104857600
  Topic: __consumer_offsets       Partition: 0    Leader: -1      Replicas: 1     Isr: 1
  Topic: __consumer_offsets       Partition: 1    Leader: 2       Replicas: 2     Isr: 2
  
  Topic: __consumer_offsets       Partition: 49   Leader: 2       Replicas: 2     Isr: 2
  </code></pre>
  
  <p>Is this a configuration error? And how can I get the consumer lag in this case? The "Leader: -1" is an error? if I shutdown the machine 1 forever, it's still work fine?</p>