zookeeper connection timing out, kafa-spark streaming - apache-spark

Question

I'm trying some exercise with spark streaming with kafka. If I use kafka producer and consumer in command line, I can publish and consume the messages in kafka. When I try to do it using pyspark in jupyter notebook. I am getting zookeeper connection timeout error.
Client session timed out, have not heard from server in 6004ms for sessionid 0x0, closing socket connection and attempting reconnect
[2017-08-04 15:49:37,494] INFO Initiating client connection, connectString=127.0.0.1:2181 sessionTimeout=6000 watcher=org.I0Itec.zkclient.ZkClient#158da8e (org.apache.zookeeper.ZooKeeper)
[2017-08-04 15:49:37,524] INFO Waiting for keeper state SyncConnected (org.I0Itec.zkclient.ZkClient)
[2017-08-04 15:49:37,527] INFO Opening socket connection to server 127.0.0.1/127.0.0.1:2181. Will not attempt to authenticate using SASL (unknown error) (org.apache.zookeeper.ClientCnxn)
[2017-08-04 15:49:37,533] WARN Session 0x0 for server null, unexpected error, closing socket connection and attempting reconnect (org.apache.zookeeper.ClientCnxn)
java.net.ConnectException: Connection refused
at sun.nio.ch.SocketChannelImpl.checkConnect(Native Method)
at sun.nio.ch.SocketChannelImpl.finishConnect(SocketChannelImpl.java:717)
at org.apache.zookeeper.ClientCnxnSocketNIO.doTransport(ClientCnxnSocketNIO.java:361)
at org.apache.zookeeper.ClientCnxn$SendThread.run(ClientCnxn.java:1141)
[2017-08-04 15:49:38,637] INFO Opening socket connection to server 127.0.0.1/127.0.0.1:2181. Will not attempt to authenticate using SASL (unknown error) (org.apache.zookeeper.ClientCnxn)
[2017-08-04 15:49:38,639] WARN Session 0x0 for server null, unexpected error, closing socket connection and attempting reconnect (org.apache.zookeeper.ClientCnxn)
java.net.ConnectException: Connection refused
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Answer 1

Zookeeper has issues when using localhost (127.0.0.1). Described in https://issues.apache.org/jira/browse/ZOOKEEPER-1661?focusedCommentId=13599352
This little program explains the following things:
ZooKeeper does call InetAddress.getAllByName (see StaticHostProvider:60) on the connect string "localhost:2181" => as a result it gets 3 different addresses for localhost which then get shuffled (Collections.shuffle(this.serverAddresses): L72
Because of the shuffling (random), the call to StaticHostProvider.next will sometime return the fe80:0:0:0:0:0:0:1%1 address which as you can see from this small program times out after 5s => this explains the randomness I am experiencing.
It really seems to me that what I am experiencing is a reverse dns lookup issue with IPv6. Whether this reverse dns lookup is actually useful and required by ZooKeeper, I do not know. It did not behave this way in 3.3.3.
Solution, specify your zookeeper address as a FQDN and make sure the reverse lookup works or use 0.0.0.0 instead of localhost.