Kafka - AdminClient - Connection to node -1 could not be established. Broker may not be available

A short post to help Googlers. On a single-node sandbox Apache Kafka / Confluent Platform installation, I was getting this error

WARN [AdminClient clientId=adminclient-3] Connection to node -1 could not be established. Broker may not be available. (org.apache.kafka.clients.NetworkClient)

I had correctly set the machine's hostname in my Kafka server.properties:


but in Schema Registry, Connect etc I had not, and so they were using the default (localhost). The AdminClient bit comes in because when they launch each creates its own internal topics.

Based on my /etc/hosts we can see localhost has a different IP from the hostname (proxmox01):

rmoff@proxmox01 ~> cat /etc/hosts localhost.localdomain localhost proxmox01.moffatt.me proxmox01  

Thus, Kafka was listening on one IP (

rmoff@proxmox01 ~> sudo netstat -plnt|grep 9092  
tcp6       0      0     :::*                    LISTEN      30345/java  

But Schema Registry and Kafka Connect were trying (and failing) to connect to it on another (localhost127.0.0.1). With the appropriate files fixed (connect-avro-distributed.properties, schema-registry.properties) all was well with the world!

I also hit a hostname/networking related error earlier in this process, which stopped Kafka launching entirely:

kafka.common.KafkaException: Socket server failed to bind to proxmox01.moffatt.me:9092: Cannot assign requested address.

Turns out my /etc/hosts was fubar - it had the wrong IP address listed for the hostname. Instead of proxmox01.moffatt.me proxmox01 

it had proxmox01.moffatt.me proxmox01 

which was wrong. Fixing this solved the problem.

Robin Moffatt

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Yorkshire, UK