Zookeeper keeps getting the WARN: "caught end of stream exception"

I am now using a CDH-5.3.1 cluster with three zookeeper instances located in three ips:

133.0.127.40 n1
133.0.127.42 n2
133.0.127.44 n3

Everything works fine when it starts, but these days I notice that the node n2 keeps getting the WARN:

caught end of stream exception

EndOfStreamException: Unable to read additional data from client sessionid **0x0**, likely client has closed socket
    at org.apache.zookeeper.server.NIOServerCnxn.doIO(NIOServerCnxn.java:220)
    at org.apache.zookeeper.server.NIOServerCnxnFactory.run(NIOServerCnxnFactory.java:208)
    at java.lang.Thread.run(Thread.java:722)

it happens every second, and only on n2, while n1 and n3 are fine. I can still use HBase shell to scan my table, and the Solr WEB UI to do querys. But I cannot start Flume agents, the process all stops at this step:

Logging to org.slf4j.impl.Log4jLoggerAdapter(org.mortbay.log) via org.mortbay.log.Slf4jLog

jetty-6.1.26.cloudera.4

Started [email protected]:41414.

And minutes later I get the warning from Cloudera Manager that Flume agent is exceeding the threshold of File Descriptors.

Does anyone know what is going wrong? Thanks in advance.

I recall seeing similar errors in ZK (admittedly not with Flume). I believe the problem at the time was to do with the large amount of data stored on the node and/or transferred to the client. Things to consider tweaking in zoo.cfg:

put a limit on autopurge.snapRetainCount, e.g. set it to 10
set autopurge.purgeInterval to, say, 2 (hours)

If the ZK client (Flume?) is streaming large znodes to/from the ZK cluster, you may want to set the Java system property jute.maxbuffer on the client JVM(s), and possibly on the server nodes, to a large enough value. I believe the default value for this property is 1M. Determining the appropriate value for your workload is an exercise in trial and error I'm afraid!

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