ZooKeeper入门指南

ZooKeeper使用log4j记录消息-有关详细信息，请参阅《程序员指南》的“记录”部分。您将看到进入控制台的日志消息（默认）和/或一个日志文件，具体取决于log4j配置。

此处概述的步骤以独立模式运行ZooKeeper。没有集群，因此，如果ZooKeeper进程失败，该服务将关闭。这对于大多数开发情况都很好，但是要以集群方式运行ZooKeeper，请参阅“运行ZooKeeper集群”。

Managing ZooKeeper Storage

For long running production systems ZooKeeper storage must be managed externally (dataDir and logs). See the section on maintenance for more details.

Connecting to ZooKeeper

管理ZooKeeper存储

对于长时间运行的生产系统，必须从外部管理ZooKeeper存储（dataDir和日志）。有关更多详细信息，请参见维护部分。

连接到ZooKeeper

$ bin/zkCli.sh -server 127.0.0.1:2181

This lets you perform simple, file-like operations.

Once you have connected, you should see something like:

这使您可以执行简单的类似文件的操作。

连接后，您应该会看到类似以下内容的信息：

Connecting to localhost:2181 log4j:WARN No appenders could be found for logger (org.apache.zookeeper.ZooKeeper). log4j:WARN Please initialize the log4j system properly. Welcome to ZooKeeper! JLine support is enabled [zkshell: 0]

From the shell, type
help
to get a listing of commands that can be executed from the client, as in:

在shell中，键入

help

以获取可以在客户端执行的命令的列表，如下所示：

[zkshell: 0] help ZooKeeper -server host:port cmd args addauth scheme auth close config [-c] [-w] [-s] connect host:port create [-s] [-e] [-c] [-t ttl] path [data] [acl] delete [-v version] path deleteall path delquota [-n|-b] path get [-s] [-w] path getAcl [-s] path getAllChildrenNumber path getEphemerals path history listquota path ls [-s] [-w] [-R] path ls2 path [watch] printwatches on|off quit reconfig [-s] [-v version] [[-file path] | [-members serverID=host:port1:port2;port3[,...]*]] | [-add serverId=host:port1:port2;port3[,...]]* [-remove serverId[,...]*] redo cmdno removewatches path [-c|-d|-a] [-l] rmr path set [-s] [-v version] path data setAcl [-s] [-v version] [-R] path acl setquota -n|-b val path stat [-w] path sync path

From here, you can try a few simple commands to get a feel for this simple command line interface. First, start by issuing the list command, as in
ls
, yielding:

从这里，您可以尝试一些简单的命令，以了解这种简单的命令行界面。首先，如中下所示

ls

发出list命令，得到：

[zkshell: 8] ls / [zookeeper]

Next, create a new znode by running
create /zk_test my_data
. This creates a new znode and associates the string “my_data” with the node. You should see:

接下来，通过运行创建一个新的znode

create /zk_test my_data

。这将创建一个新的znode并将字符串“ my_data”与该节点关联。您应该看到：

[zkshell: 9] create /zk_test my_data Created /zk_test

Issue another
ls /
command to see what the directory looks like:

发出另一个

ls /

命令以查看目录的情况：

[zkshell: 11] ls / [zookeeper, zk_test]

Notice that the zk_test directory has now been created.

Next, verify that the data was associated with the znode by running the
get
command, as in:

请注意，现在已创建zk_test目录。

接下来，通过运行

get

命令来验证数据是否与znode关联，如下所示：

[zkshell: 12] get /zk_test my_data cZxid = 5 ctime = Fri Jun 05 13:57:06 PDT 2009 mZxid = 5 mtime = Fri Jun 05 13:57:06 PDT 2009 pZxid = 5 cversion = 0 dataVersion = 0 aclVersion = 0 ephemeralOwner = 0 dataLength = 7 numChildren = 0

We can change the data associated with zk_test by issuing the
set
command, as in:

我们可以通过发出

set

命令来更改与zk_test相关的数据，如下所示：

[zkshell: 14] set /zk_test junk cZxid = 5 ctime = Fri Jun 05 13:57:06 PDT 2009 mZxid = 6 mtime = Fri Jun 05 14:01:52 PDT 2009 pZxid = 5 cversion = 0 dataVersion = 1 aclVersion = 0 ephemeralOwner = 0 dataLength = 4 numChildren = 0 [zkshell: 15] get /zk_test junk cZxid = 5 ctime = Fri Jun 05 13:57:06 PDT 2009 mZxid = 6 mtime = Fri Jun 05 14:01:52 PDT 2009 pZxid = 5 cversion = 0 dataVersion = 1 aclVersion = 0 ephemeralOwner = 0 dataLength = 4 numChildren = 0

(Notice we did a
get
after setting the data and it did, indeed, change.

Finally, let’s
delete
the node by issuing:

（请注意，我们在设置数据后做了一个改变，

get确认

确实发生了变化。

最后，通过发出以下命令

delete

来删除节点：

[zkshell: 16] delete /zk_test [zkshell: 17] ls / [zookeeper] [zkshell: 18]

That’s it for now. To explore more, see the Zookeeper CLI.

现在就这样。要了解更多信息，请参见Zookeeper CLI。

Programming to ZooKeeper

ZooKeeper has a Java bindings and C bindings. They are functionally equivalent. The C bindings exist in two variants: single threaded and multi-threaded. These differ only in how the messaging loop is done. For more information, see the Programming Examples in the ZooKeeper Programmer’s Guide for sample code using the different APIs.

Running Replicated ZooKeeper

Running ZooKeeper in standalone mode is convenient for evaluation, some development, and testing. But in production, you should run ZooKeeper in replicated mode. A replicated group of servers in the same application is called a quorum, and in replicated mode, all servers in the quorum have copies of the same configuration file.

针对ZooKeeper编程

ZooKeeper具有Java绑定和C绑定。它们在功能上是等效的。C绑定存在两种变体：单线程和多线程。这些区别仅在于消息传递循环的完成方式。有关更多信息，请参见《ZooKeeper程序员指南》中的“编程示例”，以获取使用不同API的示例代码。

运行集群的ZooKeeper

以独立模式运行ZooKeeper便于评估，某些开发和测试。但是在生产中，您应该在集群模式下运行ZooKeeper。同一应用程序中的一组服务器的集群组称为（quorum）仲裁，并且在集群模式下，仲裁中的所有服务器都具有相同配置文件的副本。

Note

For replicated mode, a minimum of three servers are required, and it is strongly recommended that you have an odd number of servers. If you only have two servers, then you are in a situation where if one of them fails, there are not enough machines to form a majority quorum. Two servers are inherently less stable than a single server, because there are two single points of failure.

The required conf/zoo.cfg file for replicated mode is similar to the one used in standalone mode, but with a few differences. Here is an example:

注意

对于集群模式，至少需要三个服务器，并且强烈建议您使用奇数个服务器。如果只有两台服务器，那么您将处于一种情况，如果其中一台服务器发生故障，则没有足够的计算机构成多数仲裁。由于存在两个单点故障，因此两个服务器就不如单个服务器稳定。

集群模式所需的conf / zoo.cfg文件类似于独立模式下使用的文件，但有一些区别。这是一个例子：

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

The new entry, initLimit is timeouts ZooKeeper uses to limit the length of time the ZooKeeper servers in quorum have to connect to a leader. The entry syncLimit limits how far out of date a server can be from a leader.

With both of these timeouts, you specify the unit of time using tickTime. In this example, the timeout for initLimit is 5 ticks at 2000 milliseconds a tick, or 10 seconds.

The entries of the form server.X list the servers that make up the ZooKeeper service. When the server starts up, it knows which server it is by looking for the file myid in the data directory. That file has the contains the server number, in ASCII.

Finally, note the two port numbers after each server name: " 2888" and “3888”. Peers use the former port to connect to other peers. Such a connection is necessary so that peers can communicate, for example, to agree upon the order of updates. More specifically, a ZooKeeper server uses this port to connect followers to the leader. When a new leader arises, a follower opens a TCP connection to the leader using this port. Because the default leader election also uses TCP, we currently require another port for leader election. This is the second port in the server entry.

新条目initLimit是超时ZooKeeper用于限制仲裁中的ZooKeeper服务器必须连接到领导者的时间长度。条目syncLimit限制服务器与领导者之间过时的差距。

对于这两个超时，您都可以使用tickTime指定时间单位。在此示例中，initLimit的超时是5心跳数，即2000毫秒/心跳数，即10秒。

表格_server.X_的条目列出了组成ZooKeeper服务的服务器。服务器启动时，它通过在数据目录中查找文件_myid_来知道它是哪台服务器。该文件包含ASCII格式服务器号。

最后，记下每个服务器名称后的两个端口号：“ 2888”和“ 3888”。对等方使用前一个端口连接到其他对等方。这样的连接是必要的，以便对等方可以进行通信，例如，同意更新顺序。更具体地说，ZooKeeper服务器使用此端口将关注者连接到领导者。当出现新的领导者时，跟随者使用此端口打开与领导者的TCP连接。因为默认的领导者选举也使用TCP，所以我们当前需要另一个端口来进行领导者选举。这是服务器条目中的第二个端口。(第一个端口节点间通信，第二个端口用于leader选举)

If you want to test multiple servers on a single machine, specify the servername as localhost with unique quorum & leader election ports (i.e. 2888:3888, 2889:3889, 2890:3890 in the example above) for each server.X in that server’s config file. Of course separate _dataDir_s and distinct _clientPort_s are also necessary (in the above replicated example, running on a single localhost, you would still have three config files).

Please be aware that setting up multiple servers on a single machine will not create any redundancy. If something were to happen which caused the machine to die, all of the zookeeper servers would be offline. Full redundancy requires that each server have its own machine. It must be a completely separate physical server. Multiple virtual machines on the same physical host are still vulnerable to the complete failure of that host.

If you have multiple network interfaces in your ZooKeeper machines, you can also instruct ZooKeeper to bind on all of your interfaces and automatically switch to a healthy interface in case of a network failure. For details, see the Configuration Parameters.

注意

如果要在一台计算机上测试多台服务器，请为每台服务器指定服务器名称为_localhost，_并具有唯一的仲裁和领导者选择端口（例如，在上面的示例中为2888：3888、2889：3889、2890：3890）。配置文件。当然，也需要单独的_dataDir_s和不同的_clientPort_s（在上面的复制示例中，在单个_localhost_上运行，您仍然会有三个配置文件）。