check can block RPC thread
</li>
<li>[<a href='https://issues.apache.org/jira/browse/FLINK-18663'>FLINK-18663</a>] -         RestServerEndpoint may prevent server shutdown
</li>
<li>[<a href='https://issues.apache.org/jira/browse/FLINK-18677'>FLINK-18677</a>] -         ZooKeeperLeaderRetrievalService does not invalidate leader in case of SUSPENDED connection
</li>
<li>[<a href='https://issues.apache.org/jira/browse/FLINK-18702'>FLINK-18702</a>] -         Flink elasticsearch connector leaks threads and class