Apache Kafka是分布式發布-訂閱消息系統。它最初由LinkedIn公司開發，之后成為Apache項目的一部分。Kafka是一種快速、可擴展的、設計內在就是分布式的，分區的和可復制的提交日志服務。
現在很多開源分布式系統，例如Flume(數據實時分析)，Storm(數據實時處理)，Spark(內存數據處理)，elasticsearch(全文檢索)
幾種分布式系統的對比

2017-05-05_095912.png

AMQP協議

kafka借鑒AMQP協議進行開發
基本概念

• 消費者(Consumer)：從消息隊列中請求消息的客戶端應用程序
• 生產者(Producer)：向Broker發布消息的客戶端應用程序。
• AMQP服務器端(Broker)：用于接收生產者發送的消息并將消息路由給服務器中隊列。
• 話題（Topic）：是特定類型的消息流。消息是字節的有效負載（Payload），話題是消息的分類名或種子（Feed）名。類似新聞中的體育，娛樂，教育等概念。實際應用中往往一個業務一個主題。

• 分區(Partition)：topic中的消息按照分區來進行組織。其是kafka消息隊列組織的最小單位，一個分區可以看作一個FIFO隊列。

  
  
• 備份(Replication)：為了保證分布式高可靠性，kafka0.8開始對每個分區數據進行備份，防止一個Broker宕機導致分區數據中數據不可用

zookeeper配置

配置zookeeper需要先配置JAVA_HOME，注意下JAVA_HOME的配置方法如下：

JAVA_HOME=/usr/local/jdk1.8
export PATH=$JAVA_HOME/bin:$PATH

一般將系統的環境變量PATH寫在后面，因為系統讀取環境變量是從前往后找的，如果PATH中本來已經配置了JAVA_HOME，那么將其放在后面可以讓我們配置的JAVA_HOME優先被讀取到。
配置完java的環境變量后，需要配置zookeeper的conf/目錄下的zoo.cfg文件。將zoo_sample.cfg拷貝為zoo.cfg后，修改內容為下：

# The number of milliseconds of each tick
# 即下面計時方式的單位
tickTime=2000
# The number of ticks that the initial 
# synchronization phase can take
# 20S，即這個時間內，集群中的機器都要啟動
initLimit=10
# The number of ticks that can pass between 
# sending a request and getting an acknowledgement
# leader發送給follower的心跳超時時間
syncLimit=5
# the directory where the snapshot is stored.
# do not use /tmp for storage, /tmp here is just 
# example sakes.
# 設置了zookeeper的dataDir以及DataLogDir，注意下這兩個目錄不要設
# 置為同一個，那樣的話會影響到zookeeper的性能。
dataDir=/home/eversilver/silverTest/kafka/zkData
# 這里存放的是zookeeper的事務日志，一般很多，需要定期的去清理，否
# 則產生很多垃圾，拖慢響應速度。官方文檔只給出了具體的清理方法
dataLogDir=/home/eversilver/silverTest/kafka/zookeeper/zkLog
# the port at which the clients will connect
clientPort=2181
# the maximum number of client connections.
# increase this if you need to handle more clients
#maxClientCnxns=60
#
# Be sure to read the maintenance section of the 
# administrator guide before turning on autopurge.
#
# http://zookeeper.apache.org/doc/current/zookeeperAdmin.html#sc_maintenance
#
# The number of snapshots to retain in dataDir
#autopurge.snapRetainCount=3
# Purge task interval in hours
# Set to "0" to disable auto purge feature
#autopurge.purgeInterval=1
# 設置zookeeper的服務器集群，集群一般設置為基數臺，當前機器對應
# 的集群id為1，有幾臺機器就配置幾行，這里有三臺機器。
# 機器名稱=機器IP:leader與follower之間通信端口:leader選舉的端口
# 注意，所以集群中的機器上面的端口應該對應相同
server.1=192.168.142.133:12888:13888
server.2=192.168.142.134:12888:13888
server.3=192.168.142.135:12888:13888

cfg文件配置完成后，在cfg文件中的dataDir目錄下新建一個myid文件，代表當前機器的id，這個id與上面server.后面的值相同即可：

eversilver@debian:/usr/local/zookeeper$ cat ~/silverTest/kafka/zookeeper/zkData/myid 
1

然后即可啟動本機，有幾臺機器即啟動幾臺：

eversilver@debian:/usr/local/zookeeper$ ./bin/zkServer.sh start
ZooKeeper JMX enabled by default
Using config: /usr/local/zookeeper/bin/../conf/zoo.cfg
Starting zookeeper ... STARTED
eversilver@debian:/usr/local/zookeeper$ jps
25846 Jps
25822 QuorumPeerMain
eversilver@debian:/usr/local/zookeeper$ 

這里啟動了三臺虛擬機上的zookeeper，可以通過zkServer.sh status來查看zookeeper運行狀態

# debian
eversilver@debian:/usr/local/zookeeper$ ./bin/zkServer.sh status
/usr/local/jdk1.8/bin/java
ZooKeeper JMX enabled by default
Using config: /usr/local/zookeeper/bin/../conf/zoo.cfg
Client port found: 2181. Client address: localhost.
Mode: follower

#debian2
eversilver@debian:/usr/local/zookeeper$ ./bin/zkServer.sh status
/usr/local/jdk1.8/bin/java
ZooKeeper JMX enabled by default
Using config: /usr/local/zookeeper/bin/../conf/zoo.cfg
Client port found: 2181. Client address: localhost.
Mode: leader

#debian3
eversilver@debian:/usr/local/zookeeper$ ./bin/zkServer.sh status
/usr/local/jdk1.8/bin/java
ZooKeeper JMX enabled by default
Using config: /usr/local/zookeeper/bin/../conf/zoo.cfg
Client port found: 2181. Client address: localhost.
Mode: follower

上面三臺機器中，debian2機器被選作了leader
leader主要作用是從客戶端接受并且響應請求
follower的主要作用:從leader同步數據，再leader關閉時，進行投票選舉出集群中的新的leader

集群搭建中的幾個重要的文件分別為：
myid文件：用于zookeeper機器間互相發現彼此
zoo.cfg：集群配置文件
log4j.properties文件：zk集群的日志輸出文件，同樣在conf目錄下
zkEnv.sh以及zkServer.sh：分別用于啟動環境配置以及集群啟動

注意，/bin目錄下的zkCleanUp.sh腳本可以快速的對zookeeper生成的日志進行清理，這里使用crontab定期執行其來進行清理。
crontab -l來查看定時任務是否存在，crontab -e對其進行編輯。這里編輯如下。其中主要需要進行配置的配置項有broker.id,port,hostname,log.dirs,numpartitions, message.max.bytes,default,replication.factor,replica.fetch.max.bytes以及zookeeper.connect

eversilver@debian:/usr/local/zookeeper$ crontab -e
# 分別代表分鐘，小時，月，年，星期幾，命令選項
0 0 * * 0 /usr/local/zookeeper/zkCleanup.sh

kafka集群搭建

解壓縮完成kafka后，打開配置文件server.properties.配置完成的的文件如下所示。

# 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.server.KafkaConfig for additional details and defaults

############################# Server Basics #############################

# The id of the broker. This must be set to a unique integer for each broker.
# 類似zookeeper的myid字段
broker.id=1

# Switch to enable topic deletion or not, default value is false
#delete.topic.enable=true

############################# Socket Server Settings #############################

# The address the socket server listens on. It will get the value returned from 
# java.net.InetAddress.getCanonicalHostName() if not configured.
#   FORMAT:
#     listeners = security_protocol://host_name:port
#   EXAMPLE:
#     listeners = PLAINTEXT://your.host.name:9092
#listeners=PLAINTEXT://:9092


# 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
port=19092
host.name=192.168.128.128
# The number of threads handling network requests
num.network.threads=3

# The number of threads doing disk I/O
# 設置成多個的時候一般下面的logDir也設置成多個，這樣一個線程處理一個目錄，性能會好很多
# 注意下面的多個目錄往往以逗號來分割
num.io.threads=8

# The send buffer (SO_SNDBUF) used by the socket server，主要為了提高性能
socket.send.buffer.bytes=102400

# The receive buffer (SO_RCVBUF) used by the socket server
socket.receive.buffer.bytes=102400

# The maximum size of a request that the socket server will accept (protection against OOM)
# 這個數不能超過java的堆棧大小
socket.request.max.bytes=104857600


############################# Log Basics #############################

# A comma seperated list of directories under which to store log files
log.dirs=/home/eversilver/silverTest/kafka/kafka/kafkaLogs

# The default number of log partitions per topic. More partitions allow greater
# parallelism for consumption, but this will also result in more files across
# the brokers.
# topic分區數
num.partitions=2

# The number of threads per data directory to be used for log recovery at startup and flushing at shutdown.
# This value is recommended to be increased for installations with data dirs located in RAID array.
num.recovery.threads.per.data.dir=1

############################# Log Flush Policy #############################

# Messages are immediately written to the filesystem but by default we only fsync() to sync
# the OS cache lazily. The following configurations control the flush of data to disk.
# There are a few important trade-offs here:
#    1. Durability: Unflushed data may be lost if you are not using replication.
#    2. Latency: Very large flush intervals may lead to latency spikes when the flush does occur as there will be a lot of data to flush.
#    3. Throughput: The flush is generally the most expensive operation, and a small flush interval may lead to exceessive seeks.
# The settings below allow one to configure the flush policy to flush data after a period of time or
# every N messages (or both). This can be done globally and overridden on a per-topic basis.

# The number of messages to accept before forcing a flush of data to disk
#log.flush.interval.messages=10000

# The maximum amount of time a message can sit in a log before we force a flush
#log.flush.interval.ms=1000

############################# Log Retention Policy #############################

# The following configurations control the disposal of log segments. The policy can
# be set to delete segments after a period of time, or after a given size has accumulated.
# A segment will be deleted whenever *either* of these criteria are met. Deletion always happens
# from the end of the log.

# The minimum age of a log file to be eligible for deletion
# 消息失效期，7天
log.retention.hours=168

# kafka每條消息存放的最大大小
message.max.byte=5048576
#kafka集群保存消息的默認份數（副本數）
default.replication.factor=2
# 取消息的最大字節數，設置為5M
replica.fetch.max.bytes=5048576


# A size-based retention policy for logs. Segments are pruned from the log as long as the remaining
# segments don't drop below log.retention.bytes.
#log.retention.bytes=1073741824

# The maximum size of a log segment file. When this size is reached a new log segment will be created.
# 超過這個大小就不再追加文件，而是新啟動一個文件
log.segment.bytes=1073741824

# The interval at which log segments are checked to see if they can be deleted according
# to the retention policies
# 每隔這么多毫秒查看是否有失效的消息，（上面是168小時）。有的話就刪除消息
log.retention.check.interval.ms=300000
# 是否啟用log壓縮
log.cleaner.enable=false

############################# Zookeeper #############################

# Zookeeper connection string (see zookeeper docs for details).
# This is a comma separated host:port pairs, each corresponding to a zk
# server. e.g. "127.0.0.1:3000,127.0.0.1:3001,127.0.0.1:3002".
# You can also append an optional chroot string to the urls to specify the
# root directory for all kafka znodes.
zookeeper.connect=192.168.128.128:2181,192.168.128.129:2181,192.168.128.130:2181

# Timeout in ms for connecting to zookeeper
zookeeper.connection.timeout.ms=6000

三個機器都配置完成后，可以使用./bin/kafka-server.sh -daemon ./config/servers.properties命令來打開kafka。打開命令后使用jps查看運行狀態如下：

eversilver@debian:/usr/local/kafka$ jps
10273 Jps
8994 QuorumPeerMain
10026 Kafka

下面可以使用一個例子查看配置是否正確。創建一個主題。命令如下：

eversilver@debian:/usr/local/kafka$ ./bin/kafka-topics.sh --create --zookeeper localhost:2181 --replication-factor 2 --partitions 1 --topic test
Created topic "test".

查看當前的主題

eversilver@debian:/usr/local/kafka$ bin/kafka-topics.sh --list --zookeeper localhost:2181
test #當前的test主題已經存在

啟動一個kafka的生產者：

eversilver@debian:/usr/local/kafka$ bin/kafka-console-producer.sh --broker-list 192.168.128.128:19092 --topic test

另一臺機器上啟動一個kafka的消費者

eversilver@debian:/usr/local/kafka$ bin/kafka-console-consumer.sh --bootstrap-server 192.168.128.129:19092 --topic test --from-beginning

當在生產者端輸入"hello"后，消費者端也會正常顯示"hello"
同樣可以通過命令查看topic的基本信息：

eversilver@debian:/usr/local/kafka$ ./bin/kafka-topics.sh --describe --zookeeper localhost:2181 --topic test
Topic:test  PartitionCount:1    ReplicationFactor:1 Configs:
Topic: test Partition: 0    Leader: 1   Replicas: 1 Isr: 1

kafka的日志目錄下的server.log是kafka集群的機器進行leader切換時產生的日志。state.change.log日志。controller.log存放的是kafka集群中的controller所產生的日志。

zookeeper運行之后可以使用 ./bin/zkCli.sh -server 127.0.0.1:2181 可以進入zookeeper的客戶端，ls / 命令顯示的zookeeper內部狀態如下所示。

[zk: 127.0.0.1:2181(CONNECTED) 0] ls /
[admin, brokers, cluster, config, consumers, controller, controller_epoch, isr_change_notification, zookeeper]

上面的所有文件除了zookeeper文件夾是zookeeper產生的其他均為kafka所產生的。可以查看broker下面的相關信息。

[zk: 127.0.0.1:2181(CONNECTED) 12] ls /brokers
[ids, seqid, topics]
[zk: 127.0.0.1:2181(CONNECTED) 13] ls /brokers/ids
[1, 2]
[zk: 127.0.0.1:2181(CONNECTED) 14] ls /brokers/ids/1
[]
[zk: 127.0.0.1:2181(CONNECTED) 15] get /brokers/ids/1
{"jmx_port":-1,"timestamp":"1494050585414","endpoints":["PLAINTEXT://192.168.128.128:19092"],"host":"192.168.128.128","version":3,"port":19092}

上面顯示了ids1的啟動時間，端口號，版本

 [zk: 127.0.0.1:2181(CONNECTED) 16] ls /brokers/topics
[__consumer_offsets, my-first-kafka-topic, test]
[zk: 127.0.0.1:2181(CONNECTED) 17] get /brokers/topics/test
{"version":1,"partitions":{"0":[1]}}

上面顯示了當前存在的所有的topic。例如其中的test topic，只有一個分區 ，版本是1.

kafka的config文件夾下的，consumer.properties配置項如下：

eversilver@debian:/usr/local/kafka$ cat ./config/consumer.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.consumer.ConsumerConfig for more details

# Zookeeper connection string
# comma separated host:port pairs, each corresponding to a zk
# server. e.g. "127.0.0.1:3000,127.0.0.1:3001,127.0.0.1:3002"
zookeeper.connect=127.0.0.1:2181

# timeout in ms for connecting to zookeeper
zookeeper.connection.timeout.ms=6000

# consumer group id
# 用來組合一個topic下面的多個partition，如果一個topic有兩個group-id，那么
# 一個group-id對應于一個consumer組。不同consumer組可以復制消費這個topic的
# 消息。即一個topic消息可以被兩個group拿兩次。
group.id=test-consumer-group

#consumer timeout
#consumer.timeout.ms=5000

kafka的config文件夾下的，producer.properties配置項也需要注意些。
注意，kafka的配置項優先級最高的是程序中設置的配置項，其次是shell中開始命令時的配置項，最低的是配置文件中設置的配置項。

相關資料：
http://kafka.apache.org/quickstart : kafka快速開始
http://kafka.apache.org/documentation/#brokerconfigs ： broker配置項以及其他的配置項。