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)