【ZooKeeper是Apache Hadoop下的开源软件，是一个分布式的协调器，本文来自于Zookeeper的官方网站，地址为：http://zookeeper.apache.org/doc/r3.4.5/zookeeperAdmin.html】

ZooKeeper Administrator's Guide：A Guide to Deployment and Administration

ZooKeeper部署和管理手册

Deployment

部署

This section contains information about deploying Zookeeper and covers these topics:

• System Requirements
• Clustered (Multi-Server) Setup
• Single Server and Developer Setup

The first two sections assume you are interested in installing ZooKeeper in a production environment such as a datacenter. The final section covers situations in whichyou are setting up ZooKeeper on a limited basis - for evaluation, testing, ordevelopment - but not in a production environment.

这一部分包含部署ZooKeeper的内容，包含如下方面：

• 系统要求
• 集群搭建
• 单服务器和开发机搭建

前两方面假设你对生产环境中安装ZooKeeper有性趣，后一部分假设你想评估、测试和开发，而不是在生产环境中部署，因而搭建的ZooKeeper有些限制。

SystemRequirements

系统要求

Supported Platforms

• GNU/Linux is supported as a development and production platform for both server and client.
• Sun Solaris is supported as a development and production platform for both server and client.
• FreeBSD is supported as a development and production platform for clients only. Java NIO selector support in the FreeBSD JVM is broken.
• Win32 is supported as a development platform only for both server and client.
• MacOSX is supported as a development platform only for both server and client.

Required Software

ZooKeeperruns in Java, release 1.6 or greater (JDK 6 or greater). It runs as anensembleof ZooKeeper servers. Three ZooKeeper servers is the minimum recommended sizefor an ensemble, and we also recommend that they run on separate machines. AtYahoo!, ZooKeeper is usually deployed on dedicated RHEL boxes, with dual-coreprocessors, 2GB of RAM, and 80GB IDE hard drives.

支持的平台

• 无论生产环境和开发环境，服务器和客户端支持GNU/Linux
• 无论生产环境和开发环境，服务器和客户端支持Sun Solaris
• 无论生产环境和开发环境，仅客户端支持FreeBSD。 FreeBSD JVM已不支持Java NIO selector了。
• 服务器和客户端支持Win32，仅适用于开发环境
• 服务器和客户端支持MacOSX，仅适用于开发环境

要求的软件

ZooKeeper在Java1.6或之上(JDK 6或之上)运行，若干ZooKeeper服务器作为一个ensemble运行，三台ZooKeeper服务器是一个ensemble最小台数要求，同时我们建议它们运行在不同的机器上。在Yahoo!，ZooKeeper通常被部署在专门的RHEL（Red Hat Enterprise Linux）机器上，双核、2GB RAM以及80GB IDE硬盘。

Clustered (Multi-Server) Setup

集群（多服务器）安装

For reliable ZooKeeper service, you should deploy ZooKeeper in a cluster known as anensemble.As long as a majority of the ensemble are up, the service will be available.Because Zookeeper requires a majority, it is best to use an odd number ofmachines. For example, with four machines ZooKeeper can only handle the failureof a single machine; if two machines fail, the remaining two machines do not constitute a majority. However, with five machines ZooKeeper can handle thefailure of two machines.

Here are thesteps to setting a server that will be part of an ensemble. These steps shouldbe performed on every host in the ensemble:

1. Install the Java JDK. You can use the native packaging system for your system, or download the JDK from:http://java.sun.com/javase/downloads/index.jsp
2. Set the Java heap size. This is very important to avoid swapping, which will seriously degrade ZooKeeper performance. To determine the correct value, use load tests, and make sure you are well below the usage limit that would cause you to swap. Be conservative - use a maximum heap size of 3GB for a 4GB machine.
3. Install the ZooKeeper Server Package. It can be downloaded from:http://zookeeper.apache.org/releases.html
4. Create a configuration file. This file can be called anything. Use the following settings as a starting point:

   tickTime=2000
   dataDir=/var/lib/zookeeper/
   clientPort=2181
   initLimit=5
   syncLimit=2
   server.1=zoo1:2888:3888
   server.2=zoo2:2888:3888
   server.3=zoo3:2888:3888
   

   You can find the meanings of these and other configuration settings in the section Configuration Parameters. A word though about a few here:Every machine that is part of the ZooKeeper ensemble should know about every other machine in the ensemble. You accomplish this with the series of lines of the form server.id=host:port:port. The parameters host and port are straightforward. You attribute the server id to each machine by creating a file named myid, one for each server, which resides in that server's data directory, as specified by the configuration file parameter dataDir.

5. The myid file consists of a single line containing only the text of that machine's id. So myid of server 1 would contain the text "1" and nothing else. The id must be unique within the ensemble and should have a value between 1 and 255.
6. If your configuration file is set up, you can start a ZooKeeper server:

   $ java -cp zookeeper.jar:lib/slf4j-api-1.6.1.jar:lib/slf4j-log4j12-1.6.1.jar:lib/log4j-1.2.15.jar:conf \ org.apache.zookeeper.server.quorum.QuorumPeerMain zoo.cfg
   

   QuorumPeerMain starts a ZooKeeper server, JMX management beans are also registered which allows management through a JMX management console. The ZooKeeper JMX document contains details on managing ZooKeeper with JMX. See the script bin/zkServer.sh, which is included in the release, for an example of starting server instances.

7. Test your deployment by connecting to the hosts:
   • In Java, you can run the following command to execute simple operations:

     $ java -cp zookeeper.jar:lib/slf4j-api-1.6.1.jar:lib/slf4j-log4j12-1.6.1.jar:lib/log4j-1.2.15.jar:conf:src/java/lib/jline-0.9.94.jar \ org.apache.zookeeper.ZooKeeperMain -server 127.0.0.1:2181
     

   • In C, you can compile either the single threaded client or the multithreaded client: or n the c subdirectory in the ZooKeeper sources. This compiles the single threaded client:

     $ make cli_st
     

     And this compiles the mulithreaded client:

     $ make cli_mt
     

     Running either program gives you a shell in which to execute simple file-system-like operations. To connect to ZooKeeper with the multithreaded client, for example, you would run:

     $ cli_mt 127.0.0.1:2181 

要得到可靠的ZooKeeper服务，你应当将ZooKeeper部署成集群方式，即部署为一个ensemble，只要这个ensemble中大部分机器可用，则服务就可用。由于ZooKeeper需要多数原则，因此最好使用奇数台机器。例如，对4台机器，ZooKeeper只能应对单台机器故障，如果两台机器发生故障，剩下的两台将不能应用多数原则，但是，如果是5台机器，ZooKeeper能应对2台机器故障。

下面是搭建一台服务器的步骤，而这是搭建一个ensemble的组成部分，在ensemble中，应对每台主机应用这些步骤：

1. 安装Java JDK。你可用使用适合于你系统的原生包，也可用从http://java.sun.com/javase/downloads/index.jsp下载。
2. 设置Java堆大小。这个设置对避免内存换入换出很重要，而内存交换将极大地降低ZooKeeper的性能。为了正确设置这个值，采用负载测试，确保你的应用在这个使用限制之下。保守点好—对一个4GB的机器使用3GB的最大堆。
3. 安装ZooKeeper服务器包，可从http://zookeeper.apache.org/releases.html下载。
4. 创建配置文件，这个文件可以叫任何名字，采用以下设置项：

   tickTime=2000
   dataDir=/var/lib/zookeeper/
   clientPort=2181
   initLimit=5
   syncLimit=2
   server.1=zoo1:2888:3888
   server.2=zoo2:2888:3888
   server.3=zoo3:2888:3888
   

   这些设置项的意义以及其他的设置项，请参阅“Configuration Parameters”一节。这里简要说一下：
   ZooKeeper ensemble中的每一台计算机都要知道其他计算机，你需要设置像server.id=host:port:port这样形式的行，其中host和port的意义很明显，通过创建一个叫myid的文件（它在配置文件中dataDir指定的data目录下），你为每台机器分配一个server id。

5. myid文件只有一行，即计算机的id（文本方式），所以，服务器1的myid文件将只包含文字“1”，没有其他东西。这个id必须是这个ensemble中唯一的，并介于1到255之间。
6. 如果配置文件建立好了，就可以启动ZooKeeper服务器了：

   $ java -cp zookeeper.jar:lib/slf4j-api-1.6.1.jar:lib/slf4j-log4j12-1.6.1.jar:lib/log4j-1.2.15.jar:conf \ org.apache.zookeeper.server.quorum.QuorumPeerMain zoo.cfg
   

   QuorumPeerMain启动了一个ZooKeeper服务器，JMX管理的bean也注册了，这样可以通过JMX控制台来管理它们。“ZooKeeper JMX document”包含了用JMX管理ZooKeeper的更详细内容。请参阅脚本bin/zkServer.sh，它在发行的内容中，看看如何启动服务器实例。

7. 通过连接主机来验证你的部署：
   • 用Java，运行如下命令:

     $ java -cp zookeeper.jar:lib/slf4j-api-1.6.1.jar:lib/slf4j-log4j12-1.6.1.jar:lib/log4j-1.2.15.jar:conf:src/java/lib/jline-0.9.94.jar \ org.apache.zookeeper.ZooKeeperMain -server 127.0.0.1:2181
     

   • 用C，编译单线程或多线程客户端，例如，
     下面命令编译单线程客户端：

     $ make cli_st

     下面命令编译多线程客户端：

     $ make cli_mt

     运行它们中的任何一个，会给你一个shell，你就可以执行简单的像文件系统一样的操作，用多线程客户端连接ZooKeeper，运行

     $ cli_mt 127.0.0.1:2181

Single Server and Developer Setup

单服务器和开发模式安装

If you want to setup ZooKeeper for development purposes, you will probably want to setup asingle server instance of ZooKeeper, and then install either the Java or Cclient-side libraries and bindings on your development machine.

The steps to setting up a single server instance are the similar to the above, except the configuration file is simpler. You can find the complete instructions in theInstalling and Running ZooKeeper in Single Server Mode section ofthe ZooKeeper Getting Started Guide.

For information on installing the client side libraries, refer to theBindingssection of theZooKeeper Programmer's Guide.

如果你想以开发目的搭建ZooKeeper，你可能希望以单服务实例方式运行ZooKeeper，在你的开发机上安装Java或C的客户端库。

在单服务器上搭建ZooKeeper的步骤与上面类似，配置文件将更简单，请参阅“ZooKeeper Getting Started Guide”一文中“Installing and Running ZooKeeper in Single Server Mode”一节。

关于如何安装客户端库，请参阅“ZooKeeper Programmer's Guide”中“Bindings”一节。

Administration

管理

This section contains information about running and maintaining ZooKeeper and covers these topics:

• Designing a ZooKeeper Deployment
• Provisioning
• Things to Consider: ZooKeeper Strengths and Limitations
• Administering
• Maintenance
• Supervision
• Monitoring
• Logging
• Troubleshooting
• Configuration Parameters
• ZooKeeper Commands: The Four Letter Words
• Data File Management
• Things to Avoid
• Best Practices

Designing a ZooKeeper Deployment

设计一个ZooKeeper的部署方式

The reliablity of ZooKeeper rests on two basic assumptions.

1. Only a minority of servers in a deployment will fail.Failure in this context means a machine crash, or some error in the network that partitions a server off from the majority.
2. Deployed machines operate correctly. To operate correctly means to execute code correctly, to have clocks that work properly, and to have storage and network components that perform consistently.

The sections below contain considerations for ZooKeeper administrators to maximize the probability for these assumptions to hold true. Some of these arecross-machines considerations, and others are things you should consider foreach and every machine in your deployment.

Cross Machine Requirements

For the ZooKeeper service to be active, there must be a majority of non-failingmachines that can communicate with each other. To create a deployment that cantolerate the failure of F machines, you should count on deploying 2xF+1machines. Thus, a deployment that consists of three machines can handle onefailure, and a deployment of five machines can handle two failures. Note that adeployment of six machines can only handle two failures since three machines isnot a majority. For this reason, ZooKeeper deployments are usually made up ofan odd number of machines.

To achievethe highest probability of tolerating a failure you should try to make machinefailures independent. For example, if most of the machines share the same switch, failure of that switch could cause a correlated failure and bring downthe service. The same holds true of shared power circuits, cooling systems,etc.

Single Machine Requirements

If  ZooKeeper has to contend with other applications for access to resourses like storagemedia, CPU, network, or memory, its performance will suffer markedly. ZooKeeper has strong durability guarantees, which means it uses storage media to logchanges before the operation responsible for the change is allowed to complete.You should be aware of this dependency then, and take great care if you want to ensure that ZooKeeper operations aren’t held up by your media. Here are somethings you can do to minimize that sort of degradation:

• ZooKeeper's transaction log must be on a dedicated device. (A dedicated partition is not enough.) ZooKeeper writes the log sequentially, without seeking Sharing your log device with other processes can cause seeks and contention, which in turn can cause multi-second delays.
• Do not put ZooKeeper in a situation that can cause a swap. In order for ZooKeeper to function with any sort of timeliness, it simply cannot be allowed to swap. Therefore, make certain that the maximum heap size given to ZooKeeper is not bigger than the amount of real memory available to ZooKeeper. For more on this, seeThings to Avoid below.

ZooKeeper的可靠性依赖于下面两个基本的假设：

1.       整个部署中只有少数服务器会发生故障。故障在这里是指机器宕机或网络发生故障使之与其他多数机器分开。

2.       部署的机器运行正常，运行正常是指代码运行正常，时钟工作正常以及存储和网络工作正常。

本节之后各节包含了ZooKeeper管理员所考虑的使这些假设尽可能实现的东西。有些考虑因素是跨机器的，另一些则是某台或每台机器的。

跨机器方面的要求

要使ZooKeeper服务正常启动，需要多数（满足多数逻辑）机器运行正常且能相互通讯。一个部署中，如果要容忍F台机器故障，则应该有2xF+1台机器，所以，在3台机器的部署中，可以应对1台机器故障，5台机器部署中，可以应对2台故障，注意，6台机器的部署中，只能应对2台故障，因为3台机器不满足多数原则逻辑。基于此，ZooKeeper部署通常由奇数台机器组成。

为最大程度容忍机器故障，应该使机器的故障相互独立，例如，如果大部分机器共享一个开关，开关故障将产生相互关联故障，整个服务就终止了，同样，公用的供电线路，空调系统等也会有同样问题。

单机方面的要求

如果ZooKeeper需要与其他应用通讯，以获得存储、CPU、网络、内存等资源，那它的性能将会大受影响。ZooKeeper有耐用性保证，就是说，在实际的操作之前，会记录日志到介质上，你应用清楚这种依赖性，并且小心利用它，不至于因为存储介质问题而使ZooKeeper停止，这有些因素，你要考虑，来减小这类性能下降：

• ZooKeeper的日志应放到一个专门的设备上（专门的的分区是不够的）ZooKeeper顺序写日志，不要与其他进程共享日志设备，其他进程可能产生寻址或发生争夺资源，这样就会有数秒的延迟。
• 不要使ZooKeeper运行在发生内存交换的场合下。为使ZooKeeper的运行不发生延迟，简单的方法就是不发生内存换入换出。因此，确保分配给ZooKeeper的最大堆不超过它所能得到的最大实际内存，详情请参阅下面的“Things to Avoid”。

Provisioning

设置过程

Things to Consider: ZooKeeperStrengths and Limitations

需要思考的问题

Administering

管理

Maintenance

维护

Little long term maintenance is required for a ZooKeeper cluster however you must be awareof the following:

Ongoing Data Directory Cleanup

The ZooKeeper Data Directorycontains files which are a persistent copy of the znodes stored by a particularserving ensemble. These are the snapshot and transactional log files. Aschanges are made to the znodes these changes are appended to a transaction log,occasionally, when a log grows large, a snapshot of the current state of all znodes will be written to the filesystem. This snapshot supercedes all previouslogs.

A ZooKeeper server will not remove old snapshots and log files when using thedefault configuration (see autopurge below), this is the responsibility of theoperator. Every serving environment is different and therefore the requirementsof managing these files may differ from install to install (backup forexample).

ThePurgeTxnLog utility implements a simple retention policy that administratorscan use. TheAPI docscontains details on calling conventions (arguments, etc...).

In the following example the last count snapshots and their corresponding logs areretained and the others are deleted. The value of <count> shouldtypically be greater than 3 (although not required, this provides 3 backups inthe unlikely event a recent log has become corrupted). This can be run as acron job on the ZooKeeper server machines to clean up the logs daily.

 java -cp zookeeper.jar:lib/slf4j-api-1.6.1.jar:lib/slf4j-log4j12-1.6.1.jar:lib/log4j-1.2.15.jar:conf org.apache.zookeeper.server.PurgeTxnLog <dataDir> <snapDir> -n <count>

Automatic purging of the snapshots and corresponding transaction logs was introduced inversion 3.4.0 and can be enabled via the following configuration parametersautopurge.snapRetainCount andautopurge.purgeInterval. For more on this, seeAdvancedConfiguration below.

Debug Log Cleanup (log4j)

See the section on logging inthis document. It is expected that you will setup a rolling file appender usingthe in-built log4j feature. The sample configuration file in the release tar'sconf/log4j.properties provides an example of this.

ZooKeeper集群基本上不需要长期的维护，但是，你必须清楚以下内容：

数据目录(DataDirectory)的持续清理

ZooKeeper的数据目录包含了ensemble中znode数据的持久化拷贝，它们是快照和日志文件。随着znode的变化，变化被记录到log文件，有时候，当日志变大后，所有znode当前状态的快照被写入文件系统，这个快照将取代以前的日志。

在缺省配置下，ZooKeeper服务器不会删除以前的快照和日志（参阅下面的autopurge），这个责任落在管理员身上。每个应用场合都不同，因此管理这些文件的要求也不同（例如是否备份）。

管理员可以利用工具“PurgeTxnLog”来实现管理策略，API文档包含了详细的调用说明（参数等等）。

下面的例子中，最后若干个快照和对应的日志被保留，其它被删掉。的典型值应大于3（尽管不是必需的），在ZooKeeper机器上作为cron的job来运行，就可以每天清除这些日志。

java -cp zookeeper.jar:lib/slf4j-api-1.6.1.jar:lib/slf4j-log4j12-1.6.1.jar:lib/log4j-1.2.15.jar:conf org.apache.zookeeper.server.PurgeTxnLog <dataDir> <snapDir> -n <count>

自动清除快照以及相应的日志是从3.4.0版开始的，通过设置下面的配置项实现：

autopurge.snapRetainCount，autopurge.purgeInterval，详情请参阅下面的“AdvancedConfiguration”。

调试日志清除(log4j)

请参阅本文中“logging”一节。这里假设你利用内置的log4j的功能安装一个带滚动功能的文件添加器(rolling file appender)，配置的例子包含在发行内容的conf/log4j.properties中。

Supervision

管理

You will want to have a supervisory process that manages each of your ZooKeeper server processes (JVM). The ZK server is designed to be "fail fast" meaning that it will shutdown (process exit) if an error occurs that it cannot recover from. As a ZooKeeper serving cluster is highly reliable, this means that whilethe server may go down the cluster as a whole is still active and serving requests. Additionally, as the cluster is "self healing" the failed server once restarted will automatically rejoin the ensemble w/o any manual interaction.

Having a supervisory process such as daemontools or SMF(other options for supervisory process are also available, it's up to you which one you would like to use, these are just two examples) managing your ZooKeeper server ensures that if the process does exit abnormally it will automatically be restarted and will quickly rejoin the cluster.

你可能想要一个监控程序来管理你的每一个ZooKeeper服务进程(JVM)，ZooKeeper服务为设计成”fail fast”，意思是如果它不能从错误中恢复过来，进程就会退出。由于ZooKeeper是高可用的，意思是若干服务宕掉后，整个集群依然可以正常响应请求。另外，集群是“自我恢复”的，如果发生故障的服务器重新启动后，它会自动再加入到ensemble，这中间，需要或不需要人工干预。

Monitoring

监控

The ZooKeeper service can be monitored in one of two primary ways; 1) the command port through the use of4 letter words and2)JMX. See the appropriate section for your environment/requirements.

ZooKeeper服务可以采用以下两种基本方法之一来监控：1）采用4字母命令；2）JMX。你具体的要求和环境可以请参阅本文合适的内容。

Logging

日志

ZooKeeper uses log4j version 1.2 as its logging infrastructure. The ZooKeeper default log4j.properties file resides in the confdirectory. Log4j requires that log4j.properties either be in the working directory (the directory from which ZooKeeper is run)or be accessible from the classpath.

For more information, see Log4j DefaultInitialization Procedure of the log4j manual.

ZooKeeper采用log4j 1.2版作为日志的基础架构。ZooKeeper中缺省的log4j.properties文件位于conf目录下。Log4j要求log4j.properties或者位于工作目录（ZooKeeper运行的目录）或在classpath指明的可以访问的目录。

Troubleshooting

故障处理

Server not coming up because of file corruption

A server might not be able to read its database and fail to come up because ofsome file corruption in the transaction logs of the ZooKeeper server. You willsee some IOException on loading ZooKeeper database. In such a case, make sureall the other servers in your ensemble are up and working. Use "stat"command on the command port to see if they are in good health. After you haveverified that all the other servers of the ensemble are up, you can go aheadand clean the database of the corrupt server. Delete all the files indatadir/version-2 and datalogdir/version-2/. Restart the server.

因文件损坏而使服务不能启动

一个服务可能因为不能读数据库而启动不了，日志中可以看到文件的损坏信息：在加载ZooKeeper数据库中有IOException。这种情况下，确保ensemble中其他服务器能起来并正常工作，可用“start”命令来看他们是否正常。验证其他服务器都正常工作后，你可以清理故障服务器的数据库，删除datadir/version-2 和 datalogdir/version-2/下的所有文件，重启服务器。

Configuration Parameters

配置参数

ZooKeeper's behavior is governed by the ZooKeeper configuration file. This file is designedso that the exact same file can be used by all the servers that make up a ZooKeeper server assuming the disk layouts are the same. If servers usedifferent configuration files, care must be taken to ensure that the list ofservers in all of the different configuration files match.

ZooKeeper的行为受它的配置文件控制，这个文件被设计成如果ZooKeeper中各服务器磁盘划分一样，则它可以被各服务器所共有。如果你想使各服务器使用不同的配置文件，则必须保证不同配置文件中的服务器列表相互匹配。

Minimum Configuration

Here are the minimum configuration keywords that must be defined in the configuration file:

clientPort

the port to listen for client connections; that is, the port that clients attempt to connect to.

dataDir

the location where ZooKeeper will store the in-memory database snapshots and, unless specified otherwise, the transaction log of updates to the database.

tickTime

最少配置项

以下是配置文件中最少的必须被定义的项目。

clientPort

侦听客户端连接的端口，也就是客户端连接服务器的端口

dataDir

ZooKeeper存储内存数据库快照的位置，以及对数据库进行修改的日志的位置（如果不特别指明）。

注：小心你放日志的位置。采用专门的日志设备是保持好性能的关键，将日志放到一个忙碌的设备上将大大损失性能。

tickTime

一次tick的时间（毫秒），它是ZooKeeper使用的基本时间单位，心跳、超时的时间都由它来规定。例如，最小的session过期时间是2个tick。

Advanced Configuration

The configuration settings in the section are optional. You can use them to furtherfine tune the behaviour of your ZooKeeper servers. Some can also be set usingJava system properties, generally of the formzookeeper.keyword. Theexact system property, when available, is noted below.

dataLogDir

(No Java system property)

globalOutstandingLimit

preAllocSize

snapCount

traceFile

maxClientCnxns

clientPortAddress

minSessionTimeout

maxSessionTimeout

fsync.warningthresholdms

autopurge.snapRetainCount

autopurge.purgeInterval

高级配置项

这节中的配置项是可选的。你可以使用它们进一步调优ZooKeeper的运行。一些也可以用Java系统的参数，它们通常采用zookeeper.keyword这样的形式。系统特有的参数（如果有），将标识在下面。

dataLogDir

globalOutstandingLimit

preAllocSize

snapCount

traceFile

maxClientCnxns

clientPortAddress

minSessionTimeout

maxSessionTimeout

fsync.warningthresholdms

autopurge.snapRetainCount

autopurge.purgeInterval

Cluster Options

The optionsin this section are designed for use with an ensemble of servers -- that is,when deploying clusters of servers.

electionAlg

(No Java system property)

initLimit

(No Java system property)

leaderServes

(Java system property: zookeeper.leaderServes)

server.x=[hostname]:nnnnn[:nnnnn], etc

(No Java system property)

syncLimit

(No Java system property)

group.x=nnnnn[:nnnnn]

(No Java system property)

weight.x=nnnnn

(No Java system property)

cnxTimeout

(Java system property: zookeeper.cnxTimeout)

集群配置项

本节中的选项是用于ensemble的，即集群部署的场合。

electionAlg

(无Java系统参数)

initLimit

(无Java系统参数)

leaderServes

(Java系统参数: zookeeper.leaderServes)

server.x=[hostname]:nnnnn[:nnnnn], etc

(无Java系统参数)

syncLimit

(无Java系统参数)

group.x=nnnnn[:nnnnn]

(无Java系统参数)

weight.x=nnnnn

(无Java系统参数)

cnxTimeout

(Java系统属性: zookeeper.cnxTimeout)

Authentication & Authorization Options

The optionsin this section allow control over authentication/authorization performed bythe service.

zookeeper.DigestAuthenticationProvider.superDigest

(Java system property only: zookeeper.DigestAuthenticationProvider.superDigest)

认证和授权配置项

本节中的选项控制Zookeeper服务的认证和授权。

zookeeper.DigestAuthenticationProvider.superDigest

(仅是Java系统的参数: zookeeper.DigestAuthenticationProvider.superDigest)

Experimental Options/Features

New features that are currently considered experimental.

Read Only Mode Server

(Java system property: readonlymode.enabled)

试验性质的选项

目前，这些新的特性是试验性质的。

Read Only Mode Server

(Java系统参数: readonlymode.enabled)

Unsafe Options

The followingoptions can be useful, but be careful when you use them. The risk of each isexplained along with the explanation of what the variable does.

forceSync

jute.maxbuffer

skipACL

不安全选项

这些选项可能有用，但必须小心使用它们，每个选项的风险与它的意义一同解释。

forceSync

jute.maxbuffer

skipACL

Communication using the Netty framework

New in 3.4:Netty isan NIO based client/server communication framework, it simplifies (over NIObeing used directly) many of the complexities of network level communicationfor java applications. Additionally the Netty framework has built in supportfor encryption (SSL) and authentication (certificates). These are optionalfeatures and can be turned on or off individually.

Prior toversion 3.4 ZooKeeper has always used NIO directly, however in versions 3.4 andlater Netty is supported as an option to NIO (replaces). NIO continues to bethe default, however Netty based communication can be used in place of NIO bysetting the environment variable "zookeeper.serverCnxnFactory" to"org.apache.zookeeper.server.NettyServerCnxnFactory". You have theoption of setting this on either the client(s) or server(s), typically youwould want to set this on both, however that is at your discretion.

TBD - tuningoptions for netty - currently there are none that are netty specific but weshould add some. Esp around max bound on the number of reader worker threadsnetty creates.

TBD - how tomanage encryption

TBD - how tomanage certificates

用Netty框架实现通讯

3.4版中的新特性：Netty是一个基于client/server的网络IO架构，对Java应用，它简化了许多复杂的网络通讯，另外，Netty架构支持加密(SSL)和认证（证书），这些是可选特性，可以被单独的打开或关上。

3.4版之前，ZooKeeper一直直接使用网络IO，但是3.4版及之后，Netty被支持作为可选的网络IO（替代）。直接进行网络IO继续是缺省值，但设置环境变量"zookeeper.serverCnxnFactory"为 "org.apache.zookeeper.server.NettyServerCnxnFactory"，基于Netty的通讯可以用来替代直接网络IO。你可以分别在客户端和服务器端分别设置，虽然这取决于你自己，但通常情况是在两边都设置为Netty。

待定—对netty的优化选项。目前还没用特定的针对netty的选项，但我们应该添加，特别是netty创建的读工作者线程的最大值。

待定—如何管理加密

待定—如何管理证书

ZooKeeper Commands: The FourLetter Words

ZooKeeper命令：4个字母的命令

ZooKeeper responds to a small set of commands. Each command is composed of four letters.You issue the commands to ZooKeeper via telnet or nc, at the client port.

Three of themore interesting commands: "stat" gives some general informationabout the server and connected clients, while "srvr" and"cons" give extended details on server and connections respectively.

ZooKeeper有一个小的命令集。每个命令由4个字母构成，你可以通过telnet或nc，在客户端端口来发出这些命令。

以下是3个有趣的命令：”stat”命令显示服务器及连接的客户端的一般信息，”srvr”和”cons”命令分别显示服务器和客户端连接的详细信息。

conf

cons

crst

dump

envi

ruok

srst

srvr

stat

wchs

wchc

wchp

mntr

$ echo mntr | nc localhost 2185zk_version  3.4.0
zk_avg_latency  0
zk_max_latency  0
zk_min_latency  0
zk_packets_received 70
zk_packets_sent 69
zk_outstanding_requests 0
zk_server_state leader
zk_znode_count   4
zk_watch_count  0
zk_ephemerals_count 0
zk_approximate_data_size    27
zk_followers    4                   - only exposed by the Leader
zk_synced_followers 4               - only exposed by the Leader
zk_pending_syncs    0               - only exposed by the Leader
zk_open_file_descriptor_count 23    - only available on Unix platforms
zk_max_file_descriptor_count 1024   - only available on Unix platforms

key \t value

Here's an example of the ruok command:

$ echo ruok | nc 127.0.0.1 5111
imok

conf

cons

crst

dump

envi

ruok

srst

srvr

stat

wchs

wchc

wchp

mntr

$ echo mntr | nc localhost 2185zk_version  3.4.0
zk_avg_latency  0
zk_max_latency  0
zk_min_latency  0
zk_packets_received 70
zk_packets_sent 69
zk_outstanding_requests 0
zk_server_state leader
zk_znode_count   4
zk_watch_count  0
zk_ephemerals_count 0
zk_approximate_data_size    27
zk_followers    4                   - only exposed by the Leader
zk_synced_followers 4               - only exposed by the Leader
zk_pending_syncs    0               - only exposed by the Leader
zk_open_file_descriptor_count 23    - only available on Unix platforms
zk_max_file_descriptor_count 1024   - only available on Unix platforms

key \t value

这里有一个ruok命令的例子：

$ echo ruok | nc 127.0.0.1 5111
imok

Data File Management

数据文件管理

ZooKeeper stores its data in a data directory and its transaction log in a transactionlog directory. By default these two directories are the same. The server can(and should) be configured to store the transaction log files in a separate directory than the data files. Throughput increases and latency decreases when transaction logs reside on a dedicated log devices.

ZooKeeper将数据保存到数据目录，事务日志保存到日志目录，缺省情况下，这两个目录相同。能够（应该）将事务日志文件配置到不同于数据目录的地方，当事务日志保存到一个专门的设备上时，就会提高吞吐量和降低延时。

The Data Directory

Thisdirectory has two files in it:

• myid - contains a single integer in human readable ASCII text that represents the server id.
• snapshot.<zxid> - holds the fuzzy snapshot of a data tree.

Each ZooKeeper server has a unique id. This id is used in two places: the myid fileand the configuration file. The myid file identifies the server that corresponds to the given data directory. The configuration file lists the contact information for each server identified byits server id. When a ZooKeeper server instance starts, it reads its id fromthe myid file and then, using that id,reads from the configuration file, looking up the port on which it should listen.

The snapshot files stored in the data directory are fuzzy snapshots in the sense that during the time the ZooKeeper server is taking the snapshot, updates are occurring tothe data tree. The suffix of the snapshot file namesis the zxid, the ZooKeeper transaction id, of the last committedtransaction at the start of the snapshot. Thus, the snapshot includes a subset of the updates to the data tree that occurred while the snapshot was inprocess. The snapshot, then, may not correspond to any data tree that actually existed, and for this reason we refer to it as a fuzzy snapshot. Still, ZooKeeper can recover using this snapshot because it takes advantage of theidempotent nature of its updates. By replaying the transaction log against fuzzy snapshots ZooKeeper gets the state of the system at the end of the log.

数据目录

这个目录有个文件：

• myid—以ASCII码形式保存的一个整数，它代表服务器id。
• Snapshot.<zxid>—保存着树形数据的“模糊“快照

每个服务器有一个唯一的id，这个id用在两个地方：myid文件和配置文件。myid文件标识了与特定数据目录相对应的服务器，配置文件列出了有sever id所标识的每台服务器的联络信息。当ZooKeeper服务器实例启动时，它从myid文件中读取id，然后，使用该id，从配置文件中读取并查找它应用监听的端口。

Snapshot文件存储在数据目录，它是“模糊“的快照，意思是，ZooKeeper一边在做树形数据快照的同时，更新也在进行。快照文件名字的后缀是zxid，即ZooKeeper事务id，这个id是快照开始之后最后提交的事务。因此，这个快照包含了快照正在进行过程中对树形数据更新的一个子集。这个快照可能并不对应实际发生的数据更新，因此我们把它叫做是“模糊“快照。但是，ZooKeeper仍然能利用快照恢复，因为它利用了更新操作的等幂性。对“模糊“快照重放事务日志，ZooKeeper能得到日志文件结束时的状态。

The Log Directory

The Log Directory contains the ZooKeeper transaction logs. Before any update takesplace, ZooKeeper ensures that the transaction that represents the update is written to non-volatile storage. A new log file is started each time a snapshotis begun. The log file's suffix is the first zxid written to that log.

日志目录

日志目录包含ZooKeeper的事务日志，任何更新发生前，ZooKeeper保证表达了更新的日志被写入持久化存储。当一个快照开始时，也开始一个新的日志文件。日志文件名的后缀是第一个被写入日志的事务id zxid。

File Management

The format ofsnapshot and log files does not change between standalone ZooKeeper servers and different configurations of replicated ZooKeeper servers. Therefore, you can pull these files from a running replicated ZooKeeper server to a development machine with a stand-alone ZooKeeper server for trouble shooting.

Using olderlog and snapshot files, you can look at the previous state of ZooKeeper serversand even restore that state. The LogFormatter class allows an administrator tolook at the transactions in a log.

The ZooKeeper server creates snapshot and log files, but never deletes them. The retention policy of the data and log files is implemented outside of the ZooKeeper server. The server itself only needs the latest complete fuzzy snapshot and the log files from the start of that snapshot. See the maintenance section in this document for more details on setting a retention policy and maintenance of ZooKeeper storage.

文件管理

Standalone部署的ZooKeeper服务器，replicated部署下不同配置的ZooKeeper服务器，快照和日志的格式都是一样的。因此，你可以将replicated部署下服务器上的这些文件拷到standalone部署下的开发机上，进行故障分析。

使用老的日志和快照文件，你可以看到ZooKeeper以前的状态，甚至恢复到这种状态。LogFormatter类允许管理员查看日志文件中的事务。

ZooKeeper服务器创建快照和日志文件，但从不删除它们。是否保留这些数据以及日志文件的策略在ZooKeeper服务器之外实现，服务器本身只需要最新的一个完整的“模糊“快照以及该快照开始之后的日志。关于更多ZooKeeper存储的保留和维护策略，参阅本文“maintenance”一节。

Things to Avoid

应避免的事情

Here are some common problems you can avoid by configuring ZooKeeper correctly:

inconsistent lists of servers

incorrect placement of transasction log

incorrect Java heap size

这有些关于正确配置ZooKeeper的常见问题，你应该避免它们。

服务器列表不一致

事务日志不正确放置

Java堆的不正确配置

Best Practices

最佳实践

For bes tresults, take note of the following list of good Zookeeper practices:

Formulti-tennant installations see the section detailing ZooKeeper "chroot" support, this can be very useful when deploying many applications/services interfacing to a single ZooKeeper cluster.

为了得到最好的结果，请记住下面使用ZooKeeper的经验：

对多租户（multi-tennant）安装，请参阅详述ZooKeeeper“chroot”支持那一节，当部署许多应用/服务到一个ZooKeeper集群时，这非常有用。

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