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I am using Kafka 0.8.2.0 (Scala 2.10). In my log files, I see the following message intermittently. This seems like a connectivity issue, but I'm running both in my localhost.

Is this a harmless warning message or should I do something to avoid it?

2015-10-30 14:12:38.015  WARN 4251 --- [ad | producer-1] [                                    ] o.apache.kafka.common.network.Selector   : Error in I/O with localhost/127.0.0.1

java.io.EOFException: null
    at org.apache.kafka.common.network.NetworkReceive.readFrom(NetworkReceive.java:62)
    at org.apache.kafka.common.network.Selector.poll(Selector.java:248)
    at org.apache.kafka.clients.NetworkClient.poll(NetworkClient.java:192)
    at org.apache.kafka.clients.producer.internals.Sender.run(Sender.java:191)
    at org.apache.kafka.clients.producer.internals.Sender.run(Sender.java:122)
    at java.lang.Thread.run(Thread.java:745)

Answers

This is a bit later to the party, but may help someone - it would have helped me.

What you're seeing occurs because the Kafka broker is passively closing the connection after a certain period of idleness is exceeded. It's defined by this broker property: connections.max.idle.ms - the default is 10 minutes.

Apparently the kafka client in 0.8.x doesn't honour that setting and just leaves idle connections open. You'll see the warning in your logs but it should have no bad effect on your application.

More details here: https://issues.apache.org/jira/browse/KAFKA-3205

The broker config is documented here: https://kafka.apache.org/090/documentation/#configuration

In that table you'll find:

Name: connections.max.idle.ms
Description: Idle connections timeout: the server socket processor threads close the connections that idle more than this
Type:long
Default: 600000

Hope that helps.