Kafka是一个分布式的、可分区的、可复制的消息系统。它提供了普通消息系统的功能，但具有自己独特的设计

• Kafka将消息以topic为单位进行归纳。
• 将向Kafka topic发布消息的程序成为producers.
• 将预订topics并消费消息的程序成为consumer.
• Kafka以集群的方式运行，可以由一个或多个服务组成，每个服务叫做一个broker.

下面来看下如何简单的使用：

首先，去官网下载kakfa的安装包 http://kafka.apache.org/downloads.html

下载完了自后，tar -zxvf *.tar.gz 解压，目录如下：

先来看下bin目录下：

从这些脚本可以看出kafka本身是结合了zookeeper来使用的

Zookeeper 协调控制
1. 管理broker与consumer的动态加入与离开。
2. 触发负载均衡，当broker或consumer加入或离开时会触发负载均衡算法，使得一
个consumer group内的多个consumer的订阅负载平衡。
3. 维护消费关系及每个partion的消费信息。

Zookeeper上的细节：
1. 每个broker启动后会在zookeeper上注册一个临时的broker registry，包含broker的ip地址和端口号，所存储的topics和partitions信息。
2. 每个consumer启动后会在zookeeper上注册一个临时的consumer registry：包含consumer所属的consumer group以及订阅的topics。
3. 每个consumer group关联一个临时的owner registry和一个持久的offset registry。对于被订阅的每个partition包含一个owner registry，内容为订阅这个partition的consumer id；同时包含一个offset registry，内容为上一次订阅的offset。

对于入门，我们就暂且使用kafka安装包中自带的zookeeper程序，这个程序在libs库中

可以看到这里有zkclient和zookeeper的依赖包，所以当我们使用该kafka程序的时候，得先启动zookeeper

再来看下config下面是什么东东：

这里就是一些具体的配置信息了

我们来看一个producer.properties

# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements.  See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License.  You may obtain a copy of the License at
#
#    http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# see kafka.producer.ProducerConfig for more details

############################# Producer Basics #############################

# list of brokers used for bootstrapping knowledge about the rest of the cluster
# format: host1:port1,host2:port2 ...
metadata.broker.list=localhost:9092

# name of the partitioner class for partitioning events; default partition spreads data randomly
#partitioner.class=

# specifies whether the messages are sent asynchronously (async) or synchronously (sync)
producer.type=sync

# specify the compression codec for all data generated: none , gzip, snappy.
# the old config values work as well: 0, 1, 2 for none, gzip, snappy, respectivally
compression.codec=none

# message encoder
serializer.class=kafka.serializer.DefaultEncoder

# allow topic level compression
#compressed.topics=

############################# Async Producer #############################
# maximum time, in milliseconds, for buffering data on the producer queue 
#queue.buffering.max.ms=

# the maximum size of the blocking queue for buffering on the producer 
#queue.buffering.max.messages=

# Timeout for event enqueue:
# 0: events will be enqueued immediately or dropped if the queue is full
# -ve: enqueue will block indefinitely if the queue is full
# +ve: enqueue will block up to this many milliseconds if the queue is full
#queue.enqueue.timeout.ms=

# the number of messages batched at the producer 
#batch.num.messages=

下面我们就来用一下，展示一下：

1、启动zookeeper

2、启动kafka

3、都启动成功了，我们就生产消费吧

创建topic

[root@com23 bin]# sh kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 1 --partitions 1 --topic CMCC
Created topic "CMCC".

生产信息

[root@com23 bin]# sh kafka-console-producer.sh --broker-list localhost:9092 --topic CMCC
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
Hwl^H^H
Hwll
Hello Kafka !

消费信息

[root@com23 bin]# sh kafka-console-consumer.sh --zookeeper localhost:2181 --topic CMCC --from-beginning
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
Hwl
Hwll
Hello Kafka !

至此，一个简单的DEMO就演示结束了，下面看看一个简单的集群怎么来玩？？

首先，我们要再配置两个服务

第一个

broker.id=1
port=9093
log.dirs=/tmp/kafka-logs-1

broker.id=2
port=9094
log.dirs=/tmp/kafka-logs-2

下面将这个两个服务也启动起来

sh bin/kafka-server-start.sh config/server-1.properties &

sh bin/kafka-server-start.sh config/server-2.properties &

下面创建topic

sh bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 3 --partitions 1 --topic chiwei

看下topic描述

[root@com23 kafka_2.10-0.8.1.1]# sh bin/kafka-topics.sh --describe --zookeeper localhost:2181 --topic chiwei
Topic:chiwei    PartitionCount:1        ReplicationFactor:3     Configs:
        Topic: chiwei   Partition: 0    Leader: 2       Replicas: 2,1,0 Isr: 2,1,0
[root@com23 kafka_2.10-0.8.1.1]# 

• "leader" is the node responsible for all reads and writes for the given partition. Each node will be the leader for a randomly selected portion of the partitions.
• "replicas" is the list of nodes that replicate the log for this partition regardless of whether they are the leader or even if they are currently alive.
• "isr" is the set of "in-sync" replicas. This is the subset of the replicas list that is currently alive and caught-up to the leader.

[root@com23 kafka_2.10-0.8.1.1]# sh bin/kafka-topics.sh --describe --zookeeper localhost:2181 --topic CMCC
Topic:CMCC      PartitionCount:1        ReplicationFactor:1     Configs:
        Topic: CMCC     Partition: 0    Leader: 0       Replicas: 0     Isr: 0

下面我们开始生产消息

[root@com23 kafka_2.10-0.8.1.1]# sh bin/kafka-console-producer.sh --broker-list localhost:9092 --topic chiwei
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
Hello Chiwei !

消费信息

[root@com23 kafka_2.10-0.8.1.1]# sh bin/kafka-console-consumer.sh --zookeeper localhost:2181 --from-beginning --topic chiwei
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
Hello Chiwei !

下面我们来测试一下这个集群的容错能力怎么样？

刚才我们看到主题描述的信息显示brokder.id=2是leader，那么我现在把leader进程给杀了，来看看什么情况啊？

ps -ef | grep server-2

kill -9 9663

[root@com23 kafka_2.10-0.8.1.1]# sh bin/kafka-topics.sh --describe --zookeeper localhost:2181 --topic chiwei
Topic:chiwei    PartitionCount:1        ReplicationFactor:3     Configs:
        Topic: chiwei   Partition: 0    Leader: 1       Replicas: 2,1,0 Isr: 1,0
[root@com23 kafka_2.10-0.8.1.1]# 

leader已经被换了，同时我们注意到replicas已然显示有2，而isr没有2了，因为isr显示的是“in-sync”的服务id，而2已经不再同步服务了；而replicas为什么还显示2呢

• "replicas" is the list of nodes that replicate the log for this partition regardless of whether they are the leader or even if they are currently alive.

这时候我们再去消费刚才主题的消息看看

[root@com23 kafka_2.10-0.8.1.1]# sh bin/kafka-console-consumer.sh --zookeeper localhost:2181 --from-beginning --topic chiwei
SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
SLF4J: Defaulting to no-operation (NOP) logger implementation
SLF4J: See http://www.slf4j.org/codes.html#StaticLoggerBinder for further details.
Hello Chiwei !

【Kafka】kafka的环境搭建，集群环境的搭建