UnknownHostException kafka

Question

I am trying to setup a Kafka cluster (the first node in the cluster actually).

I have a single node zookeeper cluster setup. I am setting up kafka on a separate node.

Both running CentOS 6.4, running IPV6 which is a bit of a PITA. I verified that the machines can talk to each other using netcat.

When I startup kafka, I am getting the following exception (which causes kafka to shut down). EDIT: I got kafka starting, I had to set the host.name property in the server.config file.

I was able to create a test topic and send messages just fine from the kafka server.

However, I get the same error when trying to consume the messages.

Any help, suggestions?

bin/kafka-console-consumer.sh --zookeeper zk1:2181 --topic test --from-beginning
Exception in thread "main" java.net.UnknownHostException: kafka: kafka: Name or service not known
    at java.net.InetAddress.getLocalHost(InetAddress.java:1473)
    at kafka.consumer.ZookeeperConsumerConnector.<init>(ZookeeperConsumerConnector.scala:107)
    at kafka.consumer.ZookeeperConsumerConnector.<init>(ZookeeperConsumerConnector.scala:128)
    at kafka.consumer.Consumer$.create(ConsumerConnector.scala:89)
    at kafka.consumer.ConsoleConsumer$.main(ConsoleConsumer.scala:178)
    at kafka.consumer.ConsoleConsumer.main(ConsoleConsumer.scala)
Caused by: java.net.UnknownHostException: kafka: Name or service not known
    at java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method)
    at java.net.InetAddress$1.lookupAllHostAddr(InetAddress.java:901)
    at java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1293)
    at java.net.InetAddress.getLocalHost(InetAddress.java:1469)
    ... 5 more

Terrarium

Internet connection, URL are correct? – Sonar

Well, I know that I can communicate from the KAFKA server to ZOOKEEPER because a leader was elected, I created a topic, and posted a sample message. It is consuming messages that isn't working. There is some configuration someplace that isn't right here, but I am not clear on what that is. – Terrarium

so I am assuming that config/server.properties does have the host.name property set properly .. what is your /etc/hosts file shows? – Nigercongo

host.name=kafka1; zookeeper.connect=zk1:2181. I have entries in the /etc/hosts file for both "kafka1" and "zk1" with the correct IPV6 addresses. Can confirm that both servers can talk to each other by using PING and "nc -z -w 1 kafka1 9092" and "nc -z -w 1 zk1 2181" – Terrarium

I am thinking there is something on the zookeeper side that I didn't setup correctly? When I see "UnknownHostException: kafka", it looks like "kafka" is a default setup someplace, and of course that is not right. – Terrarium

In that case in my opinion it would throw something like org.I0Itec.zkclient.exception.ZkException: Unable to connect to zk1:2181 & Caused by: java.net.UnknownHostException: zk1 – Nigercongo

Looked in the kafka source code, turns out that "java.net.InetAddress.getLocalHost" is not resolving on the VM, this is used to construct a default consumer.id if one is not set in the Consumer properties. – Terrarium

I am facing same error can you please tell me how did you resolved this ? java.net.UnknownHostException: QN_STG1 – Turaco

Answer 1

When you run > bin/kafka-console-consumer.sh command kafka loads a ConsoleConsumer, which will attempt to create a consumer with an auto generated consumer id. The way Kafka generates the consumer id is to concatenate the name of the local host to it. So, in the problem was the fact that java could not resolve the ip address for local host on the Open Stack VM I am working with.

So the answer was that the Open Stack VM was resolving the local host name to kafka, which is the name of the VM. I had everything setup in the Kafka and Zookeeper instances as kafka1.

So, when java was calling getLocalHost, it was trying to find the IP Address for kafka, which I did not have in my /etc/hosts file.

I simply added an entry for kafka in my /etc/hosts file and everything started working wonderfully!!!

I would have thought it would resolve to localhost, but it did not, it resolved to the name of the vm, kafka.

Terrarium

So how you kafka entry look like now? – Sprig

how does your entry look like ? – Bract

127.0.0.1 localhost 127.0.0.1 ip-172-31-0-252 – Halfcock

Editing the hosts file is only a workaround - the actual fix is to set advertised.listener correctly - see rmoff.net/2018/08/02/kafka-listeners-explained – Amoebaean

Answer 2

As noplay pointed out the issue was that Kafka wasn't able to resolve the correct IP, this may happen for example on you EC2 instances running in private subnets without assignment of public IP. The solution summarized:

hostname

Which will show you the host name, something like ip-10-180-128-217. Then just update your /etc/hosts

sudo nano /etc/hosts

edit, e.g.

127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomain4 ip-10-180-128-217

Thicket

Answer 3

Under your kafka_folder/config (sudo vim /etc/hosts), your file should look like that:

127.0.0.1 kafka localhost localhost.localdomain localhost4 localhost4.localdomain4
::1 localhost localhost.localdomain <localhost_OR_DNS_OR_ip_address>
<localhost_OR_DNS_OR_ip_address> kafka

note that kafka is my desired hostname name.

Then, under

kafka_folder/config/server.properties

there's a field "listeners=".

It looks like that

# The address the socket server listens on. If not configured, the host name will be equal to the value of
# java.net.InetAddress.getCanonicalHostName(), with PLAINTEXT listener name, and port 9092.
#   FORMAT:
#     listeners = listener_name://host_name:port
#   EXAMPLE:
#     listeners = PLAINTEXT://your.host.name:9092

Simply uncomment that field by removing the "#" before it. Should look like that:

listeners=PLAINTEXT://<localhost_OR_DNS_OR_ip_address>:9092

Fiducial

Answer 4

• if you get dns server configured kafka will consider your dns domain name so tape this command on your server

  hostname the result will be your localdomain, now copie your localdomain then open hosts file

  nano /etc/hosts add your localdomain.

  127.0.0.1 localhost localhost.localdomain "your localdomain"

  ::1 localhost localhost.localdomain "your localdomain"

Kentonkentucky