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<h1>ZooKeeper Getting Started Guide</h1>
<div id="minitoc-area">
<ul class="minitoc">
<li>
<a href="#ch_GettingStarted">Getting Started: Coordinating Distributed Applications with
      ZooKeeper</a>
<ul class="minitoc">
<li>
<a href="#sc_InstallingSingleMode">Installing and Running ZooKeeper in Single Server Mode</a>
</li>
<li>
<a href="#sc_ConnectingToZooKeeper">Connecting to ZooKeeper</a>
</li>
<li>
<a href="#sc_ProgrammingToZooKeeper">Programming to ZooKeeper</a>
</li>
<li>
<a href="#sc_RunningReplicatedZooKeeper">Running Replicated ZooKeeper</a>
</li>
<li>
<a href="#Other+Optimizations">Other Optimizations</a>
</li>
</ul>
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<a name="N10009"></a><a name="ch_GettingStarted"></a>
<h2 class="h3">Getting Started: Coordinating Distributed Applications with
      ZooKeeper</h2>
<div class="section">
<p>This document contains information to get you started quickly with
    Zookeeper. It is aimed primarily at developers hoping to try it out, and
    contains simple installation instructions for a single ZooKeeper server, a
    few commands to verify that it is running, and a simple programming
    example. Finally, as a convenience, there are a few sections regarding
    more complicated installations, for example running replicated
    deployments, and optimizing the transaction log. However for the complete
    instructions for commercial deployments, please refer to the <a href="zookeeperAdmin.html">Zookeeper
    Administrator's Guide</a>.</p>
<a name="N10016"></a><a name="sc_InstallingSingleMode"></a>
<h3 class="h4">Installing and Running ZooKeeper in Single Server Mode</h3>
<p>Setting up a ZooKeeper server in standalone mode is
      straightforward. The server is contained in a single JAR file, so
      installation consists of copying a JAR file and creating a
      configuration.</p>
<div class="note">
<div class="label">Note</div>
<div class="content">
        
<p>Zookeeper requires Java 1.5 or more recent.</p>
      
</div>
</div>
<p>Once you have downloaded the ZooKeeper source, cd to the root of
      your ZooKeeper source, and run "ant jar". For example:</p>
<pre class="code">
$ cd ~/dev/zookeeper
$ ~/dev/zookeeper/: ant jar
</pre>
<p>This should generate a JAR file called zookeeper.jar. To start
      Zookeeper, compile and run zookeeper.jar.</p>
<p>To start ZooKeeper you need a configuration file. Here is a sample
      file:</p>
<pre class="code">
tickTime=2000
dataDir=/var/zookeeper/ 
clientPort=2181
</pre>
<p>This file can be called anything, but for the sake of this
      discussion, call it <strong>zoo.cfg</strong>. Here are
      the meanings for each of the fields:</p>
<dl>
        
<dt>
<term>
<strong>tickTime</strong>
</term>
</dt>
<dd>
<p>the basic time unit in milliseconds used by ZooKeeper. It is
            used to do heartbeats and the minimum session timeout will be
            twice the tickTime.</p>
</dd>
      
</dl>
<dl>
        
<dt>
<term>
<strong>dataDir</strong>
</term>
</dt>
<dd>
<p>the location to store the in-memory database snapshots and,
            unless specified otherwise, the transaction log of updates to the
            database.</p>
</dd>

        
<dt>
<term>
<strong>clientPort</strong>
</term>
</dt>
<dd>
<p>the port to listen for client connections</p>
</dd>
      
</dl>
<p>Now that you created the configuration file, you can start
      ZooKeeper:</p>
<pre class="code">java -cp zookeeper-dev.jar:java/lib/log4j-1.2.15.jar:conf org.apache.zookeeper.server.quorum.QuorumPeerMain zoo.cfg</pre>
<p>ZooKeeper logs messages using log4j -- more detail available in
      the <a href="zookeeperProgrammers.html#Logging">Logging</a>
      section of the Programmer's Guide.<em>[tbd:
      real reference needed]</em> You will see log messages coming to the
      console and/or a log file depending on the log4j configuration.</p>
<p>The steps outlined here run ZooKeeper in standalone mode. There is
      no replication, so if Zookeeper process fails, the service will go down.
      This is fine for most development situations, but to run Zookeeper in
      replicated mode, please see <a href="#sc_RunningReplicatedZooKeeper">Running Replicated
      Zookeeper</a>.</p>
<p></p>
<a name="N10072"></a><a name="sc_ConnectingToZooKeeper"></a>
<h3 class="h4">Connecting to ZooKeeper</h3>
<p>Once ZooKeeper is running, you have several option for connection
      to it:</p>
<ul>
        
<li>
          
<p>
<strong>Java</strong>: Use java -cp
          zookeeper.jar:java/lib/log4j-1.2.15.jar:conf
          org.apache.zookeeper.ZooKeeperMain 127.0.0.1:2181</p>

          
<p>This lets you perform simple, file-like operations.</p>
        
</li>

        
<li>
          
<p>
<strong>C</strong>: compile cli_mt
          (multi-threaded) or cli_st (single-threaded) by running
          <span class="codefrag command">make cli_mt</span> or <span class="codefrag command">make cli_st</span>
          in the c subdirectory in the ZooKeeper sources.</p>

          
<p>You can run the program using <em>LD_LIBRARY_PATH=.
          cli_mt 127.0.0.1:2181</em> or <em>LD_LIBRARY_PATH=.
          cli_st 127.0.0.1:2181</em>. This will give you a simple shell
          to execute file system like operations on ZooKeeper.</p>
        
</li>
      
</ul>
<a name="N100A3"></a><a name="sc_ProgrammingToZooKeeper"></a>
<h3 class="h4">Programming to ZooKeeper</h3>
<p>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 <a href="zookeeperProgrammers.html#ch_programStructureWithExample.html">Programming
      Examples in the Zookeeper Programmer's Guide</a> for
      sample code using of the different APIs.</p>
<a name="N100B1"></a><a name="sc_RunningReplicatedZooKeeper"></a>
<h3 class="h4">Running Replicated ZooKeeper</h3>
<p>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 <em>quorum</em>, and in replicated
      mode, all servers in the quorum have copies of the same configuration
      file. The file is similar to the one used in standalone mode, but with a
      few differences. Here is an example:</p>
<pre class="code">
tickTime=2000 
dataDir=/var/zookeeper/ 
clientPort=2181 
initLimit=5 
syncLimit=2 
server.1=zoo1:2888
server.2=zoo2:2888 
server.3=zoo3:2888 
</pre>
<p>The new entry, <strong>initLimit</strong> is
      timeouts ZooKeeper uses to limit the length of time the Zookeeper
      servers in quorum have to connect to a leader. The entry <strong>syncLimit</strong> limits how far out of date a server can
      be from a leader.</p>
<p>With both of these timeouts, you specify the unit of time using
      <strong>tickTime</strong>. In this example, the timeout
      for initLimit is 5 ticks at 2000 milleseconds a tick, or 10
      seconds.</p>
<p>The entries of the form <em>server.X</em> 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.</p>
<p>Finally, note the "2888" port numbers after each server name.
      These are the "electionPort" numbers of the servers (as opposed to
      clientPorts), that is ports for <em>[tbd]</em>.</p>
<div class="note">
<div class="label">Note</div>
<div class="content">
        
<p>If you want to test multiple servers on a single machine, define
        the electionPort for each server in that server's config file, using
        the line <span class="codefrag command">electionPort=xxxx</span> as means of avoiding
        clashes.</p>
      
</div>
</div>
<a name="N100E6"></a><a name="Other+Optimizations"></a>
<h3 class="h4">Other Optimizations</h3>
<p>There are a couple of other configuration parameters that can
      greatly increase performance:</p>
<ul>
        
<li>
          
<p>To get low latencies on updates it is important to have a
          dedicated transaction log directory. By default transaction logs are
          put in the same directory as the data snapshots and *myid* file. The
          dataLogDir parameters indicates a different directory to use for the
          transaction logs.</p>
        
</li>

        
<li>
          
<p>
<em>[tbd: what is the other config param?]</em>
</p>
        
</li>
      
</ul>
</div>

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