[bug] Support "This ZooKeeper instance is not currently serving requests"

[TomaszUrugOlszewski]

Hello,

When there is no leader in Zookeeper, stat command returns :

echo stat | nc 10.0.0.7 2181
This ZooKeeper instance is not currently serving requests

Monitoring script check_zookeeper.py can't handle this situation gracefuly, and dies with

/etc/sensu/plugins/check_zookeeper.py -s 10.0.0.7:2181,10.0.0.8:2181,10.0.0.9:2181 -o nagios -w 1 -c 0 -k zk_followers
Traceback (most recent call last):
  File "/etc/sensu/plugins/check_zookeeper.py", line 369, in <module>
    sys.exit(main())
  File "/etc/sensu/plugins/check_zookeeper.py", line 287, in main
    cluster_stats = get_cluster_stats(opts.servers)
  File "/etc/sensu/plugins/check_zookeeper.py", line 325, in get_cluster_stats
    stats["%s:%s" % (host, port)] = zk.get_stats()
  File "/etc/sensu/plugins/check_zookeeper.py", line 172, in get_stats
    stat = self._parse_stat(self._send_cmd('stat'))
  File "/etc/sensu/plugins/check_zookeeper.py", line 221, in _parse_stat
    result['zk_version'] = version[version.index(':')+1:].strip()
ValueError: substring not found

Problem exists here (change in lines 218-221 is my dirty hack):

214     def _parse_stat(self, data):
215         """ Parse the output from the 'stat' 4letter word command """
216         h = StringIO(data)
217 
218         not_serving_requests = re.match("^This ZooKeeper instance is not", data)
219         if not_serving_requests:
220            print("CRITICAL: Zookeeper is out of quorum, not serving requests")
221            sys.exit(2)
222         
223         result = {}
224         
225         version = h.readline()
226         if version:
227             result['zk_version'] = version[version.index(':')+1:].strip()

I'm not sure how to fix it in legitimate way :-)