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<p>Heron relies on ZooKeeper for a wide variety of cluster coordination tasks. You
can use either a shared or dedicated ZooKeeper cluster.</p>
<p>There are a few things you should be aware of regarding Heron and ZooKeeper:</p>
<ul>
<li>Heron uses ZooKeeper only for coordination, <em>not</em> for message passing, which
means that ZooKeeper load should generally be fairly low. A single-node
and/or shared ZooKeeper <em>may</em> suffice for your Heron cluster, depending on
usage.</li>
<li>Heron uses ZooKeeper more efficiently than Storm. This makes Heron less likely
than Storm to require a bulky or dedicated ZooKeeper cluster, but your use
case may require one.</li>
<li>We strongly recommend running ZooKeeper <a href="http://zookeeper.apache.org/doc/r3.3.3/zookeeperAdmin.html#sc_supervision">under
supervision</a>.</li>
</ul>
<h3><a class="anchor" aria-hidden="true" id="zookeeper-state-manager-configuration"></a><a href="#zookeeper-state-manager-configuration" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>ZooKeeper State Manager Configuration</h3>
<p>You can make Heron aware of the ZooKeeper cluster by modifying the
<code>statemgr.yaml</code> config file specific for the Heron cluster. You'll
need to specify the following for each cluster:</p>
<ul>
<li><p><code>heron.class.state.manager</code> --- Indicates the class to be loaded for managing
the state in ZooKeeper and this class is loaded using reflection. You should set this
to <code>org.apache.heron.statemgr.zookeeper.curator.CuratorStateManager</code></p></li>
<li><p><code>heron.statemgr.connection.string</code> --- The host IP address and port to connect to ZooKeeper
cluster (e.g) &quot;127.0.0.1:2181&quot;.</p></li>
<li><p><code>heron.statemgr.root.path</code> --- The root ZooKeeper node to be used by Heron. We recommend
providing Heron with an exclusive root node; if you do not, make sure that the following child
nodes are unused: <code>/tmanagers</code>, <code>/topologies</code>, <code>/pplans</code>, <code>/executionstate</code>, <code>/schedulers</code>.</p></li>
<li><p><code>heron.statemgr.zookeeper.is.initialize.tree</code> --- Indicates whether the nodes under ZooKeeper
root <code>/tmanagers</code>, <code>/topologies</code>, <code>/pplans</code>, <code>/executionstate</code>, and <code>/schedulers</code> need to created,
if they are not found. Set it to <code>True</code> if you could like Heron to create those nodes. If those
nodes are already there, set it to <code>False</code>. The absence of this configuration implies <code>True</code>.</p></li>
<li><p><code>heron.statemgr.zookeeper.session.timeout.ms</code> --- Specifies how much time in milliseconds
to wait before declaring the ZooKeeper session is dead.</p></li>
<li><p><code>heron.statemgr.zookeeper.connection.timeout.ms</code> --- Specifies how much time in milliseconds
to wait before the connection to ZooKeeper is dead.</p></li>
<li><p><code>heron.statemgr.zookeeper.retry.count</code> --- Count of the number of retry attempts to connect
to ZooKeeper</p></li>
<li><p><code>heron.statemgr.zookeeper.retry.interval.ms</code>: Time in milliseconds to wait between each retry</p></li>
</ul>
<h3><a class="anchor" aria-hidden="true" id="example-zookeeper-state-manager-configuration"></a><a href="#example-zookeeper-state-manager-configuration" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Example ZooKeeper State Manager Configuration</h3>
<p>Below is an example configuration (in <code>statemgr.yaml</code>) for a ZooKeeper running in <code>localhost</code>:</p>
<pre><code class="hljs css language-yaml"><span class="hljs-comment"># local state manager class for managing state in a persistent fashion</span>
<span class="hljs-attr">heron.class.state.manager:</span> <span class="hljs-string">org.apache.heron.statemgr.zookeeper.curator.CuratorStateManager</span>

<span class="hljs-comment"># local state manager connection string</span>
<span class="hljs-attr">heron.statemgr.connection.string:</span>  <span class="hljs-string">"127.0.0.1:2181"</span>

<span class="hljs-comment"># path of the root address to store the state in a local file system</span>
<span class="hljs-attr">heron.statemgr.root.path:</span> <span class="hljs-string">"/heron"</span>

<span class="hljs-comment"># create the zookeeper nodes, if they do not exist</span>
<span class="hljs-attr">heron.statemgr.zookeeper.is.initialize.tree:</span> <span class="hljs-literal">True</span>

<span class="hljs-comment"># timeout in ms to wait before considering zookeeper session is dead</span>
<span class="hljs-attr">heron.statemgr.zookeeper.session.timeout.ms:</span> <span class="hljs-number">30000</span>

<span class="hljs-comment"># timeout in ms to wait before considering zookeeper connection is dead</span>
<span class="hljs-attr">heron.statemgr.zookeeper.connection.timeout.ms:</span> <span class="hljs-number">30000</span>

<span class="hljs-comment"># timeout in ms to wait before considering zookeeper connection is dead</span>
<span class="hljs-attr">heron.statemgr.zookeeper.retry.count:</span> <span class="hljs-number">10</span>

<span class="hljs-comment"># duration of time to wait until the next retry</span>
<span class="hljs-attr">heron.statemgr.zookeeper.retry.interval.ms:</span> <span class="hljs-number">10000</span>
</code></pre>
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