kafka -version 3.0.0

当把kafka部署在云服务器或者虚拟机上，使用本地主机的java客户端连接kafka进行消息的收发操作，可能在程序一开始就会产生java.net.UnknownHostException错误，这是由于没有正确配置kafka的advertised.listeners地址产生的

这是我遇到的报错信息 lavm-rl6vynrf1w: nodename nor servname provided, or not known

java.net.UnknownHostException: lavm-rl6vynrf1w: nodename nor servname provided, or not known
	at java.net.Inet6AddressImpl.lookupAllHostAddr(Native Method)
	at java.net.InetAddress$2.lookupAllHostAddr(InetAddress.java:929)
	at java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1343)
	at java.net.InetAddress.getAllByName0(InetAddress.java:1295)
	at java.net.InetAddress.getAllByName(InetAddress.java:1205)
	at java.net.InetAddress.getAllByName(InetAddress.java:1127)
	at org.apache.kafka.clients.DefaultHostResolver.resolve(DefaultHostResolver.java:27)
	at org.apache.kafka.clients.ClientUtils.resolve(ClientUtils.java:109)
	at org.apache.kafka.clients.ClusterConnectionStates$NodeConnectionState.currentAddress(ClusterConnectionStates.java:508)
	at org.apache.kafka.clients.ClusterConnectionStates$NodeConnectionState.access$200(ClusterConnectionStates.java:465)
	at org.apache.kafka.clients.ClusterConnectionStates.currentAddress(ClusterConnectionStates.java:170)
	at org.apache.kafka.clients.NetworkClient.initiateConnect(NetworkClient.java:975)
	at org.apache.kafka.clients.NetworkClient.ready(NetworkClient.java:301)
	at org.apache.kafka.clients.producer.internals.Sender.sendProducerData(Sender.java:354)
	at org.apache.kafka.clients.producer.internals.Sender.runOnce(Sender.java:327)
	at org.apache.kafka.clients.producer.internals.Sender.run(Sender.java:256)
	at java.lang.Thread.run(Thread.java:750)
17:17:51.661 [kafka-producer-network-thread | producer-1] DEBUG org.apache.kafka.clients.NetworkClient - [Producer clientId=producer-1] Give up sending metadata request since no node is available
17:17:51.712 [kafka-producer-network-thread | producer-1] DEBUG org.apache.kafka.clients.NetworkClient - [Producer clientId=producer-1] Give up sending metadata request since no node is available
17:17:51.764 [kafka-producer-network-thread | producer-1] DEBUG org.apache.kafka.clients.NetworkClient - [Producer clientId=producer-1] Give up sending metadata request since no node is available
17:17:51.815 [kafka-producer-network-thread | producer-1] DEBUG org.apache.kafka.clients.NetworkClient - [Producer clientId=producer-1] Give up sending metadata request since no node is available
17:17:51.866 [kafka-producer-network-thread | producer-1] DEBUG org.apache.kafka.clients.NetworkClient - [Producer clientId=producer-1] Give up sending metadata request since no node is available
17:17:51.917 [kafka-producer-network-thread | producer-1] DEBUG org.apache.kafka.clients.NetworkClient - [Producer clientId=producer-1] Give up sending metadata request since no node is available
17:17:51.968 [kafka-producer-network-thread | producer-1] DEBUG org.apache.kafka.clients.NetworkClient - [Producer clientId=producer-1] Give up sending metadata request since no node is available

在kafka/config/server.properties的配置文件中有一个advertised.listeners的配置(在配置文件中用esc + / + advertised.listeners 查找) 以下为默认值

# Hostname and port the broker will advertise to producers and consumers. If not set,
# it uses the value for "listeners" if configured.  Otherwise, it will use the value
# returned from java.net.InetAddress.getCanonicalHostName().
#advertised.listeners=PLAINTEXT://your.host.name:9092

这个参数的作用用于指定 Kafka Broker 向客户端（如生产者和消费者）公开的地址。它直接影响到客户端如何连接到 Kafka Broker。也就是说当客户端连接kafka进行操作，kafka会将这个地址发送给客户端，用于后续通信

那么如果客户端和kafka在同一主机上，客户端直接使用主机名也可以进行通信

如果在虚拟机或者云服务器，要么客户端在DNS中注册主机名和ip要么修改这个配置信息，暴露ip和端口

然后重启kafka

$KAFKA_HOME/bin/kafka-server-stop.sh
$KAFKA_HOME/bin/kafka-server-start.sh -daemon $KAFKA_HOME/config/server.properties

补充

客户端连接到 Broker时，会先连接到 bootstrap.servers 中指定的地址来获取元数据信息。

通过这个可以访问到kafka集群(如果存在)，而集群中的其他成员，通过这个广告地址，使得通信得以建立

这一配置确保了客户端连接时的地址与实际数据传输的地址可以不同，适用于跨网络或需要特定访问控制的环境。

应用场景

1. 可以将 Kafka 广告的地址设置为内网 IP，以限制外网访问
2. Kafka 部署在内网中，而客户端在外网访问 Kafka，advertised.listeners 设置成一个外网ip
3. Kafka 在 Docker 中运行，通过容器的 IP 连接无法访问 Kafka 实例，但可以通过宿主机的 IP 连接