kafka producer 发送消息简介

kafka 的 topic 由 partition 组成，producer 会根据 key，选择一个 partition 发送消息，而 partition 有多个副本，副本有 leader 和 follower 之分，producer 需要把消息发送到 partition 的 leader。

背景：kafka 集群由 3 个节点组成(node1，node2，node3，其中 node3 是 controller)，存在名为 idea-zhang 的 topic，只有一个 partition， partition 的副本数是2。

流程图如下：

重要日志如下：

Initialize connection to node 10.253.114.163:9092 (id: -1 rack: null) for sending metadata request (org.apache.kafka.clients.NetworkClient)
Sending metadata request (type=MetadataRequest, topics=idea-zhang) to node 10.253.114.163:9092 (id: -1 rack: null) (org.apache.kafka.clients.NetworkClient)

Completed receive from node -1 for METADATA with correlation id 1, received 
{
	throttle_time_ms = 0,
	brokers = [{
		node_id = 2,
		host = 10.253.162.17,
		port = 9092,
		rack = null
	},
	{
		node_id = 1,
		host = 10.253.160.154,
		port = 9092,
		rack = null
	},
	{
		node_id = 3,
		host = 10.253.114.163,
		port = 9092,
		rack = null
	}],
	cluster_id = oX31KEPESLeIWHz7BgJv7g,
	controller_id = 3,
	topic_metadata = [{
		error_code = 0,
		topic = idea-zhang,
		is_internal = false,
		partition_metadata = [{
			error_code = 0,
			partition = 0,
			leader = 2,
			replicas = [2, 3],
			isr = [2, 3]
		}]
	}]
}
 (org.apache.kafka.clients.NetworkClient)
 
 Initiating connection to node 10.253.162.17:9092 (id: 2 rack: null) (org.apache.kafka.clients.NetworkClient)
 
 Sending record ProducerRecord(topic=idea-zhang, partition=null, headers=RecordHeaders(headers = [], isReadOnly = true), key=1, value=Message_1, timestamp=null) with callback null to topic idea-zhang partition 0 (org.apache.kafka.clients.producer.KafkaProducer)