<!DOCTYPE html><html lang="en"><head><meta charSet="utf-8"/><meta http-equiv="X-UA-Compatible" content="IE=edge"/><title>ZooKeeper · Apache Druid</title><meta name="viewport" content="width=device-width"/><link rel="canonical" href="https://druid.apache.org/docs/0.23.0/dependencies/zookeeper.html"/><meta name="generator" content="Docusaurus"/><meta name="description" content="&lt;!--"/><meta name="docsearch:language" content="en"/><meta name="docsearch:version" content="0.23.0" /><meta property="og:title" content="ZooKeeper · Apache Druid"/><meta property="og:type" content="website"/><meta property="og:url" content="https://druid.apache.org/index.html"/><meta property="og:description" content="&lt;!--"/><meta property="og:image" content="https://druid.apache.org/img/druid_nav.png"/><meta name="twitter:card" content="summary"/><meta name="twitter:image" content="https://druid.apache.org/img/druid_nav.png"/><link rel="shortcut icon" href="/img/favicon.png"/><link rel="stylesheet" href="https://cdn.jsdelivr.net/docsearch.js/1/docsearch.min.css"/><link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/highlight.js/9.12.0/styles/default.min.css"/><script async="" src="https://www.googletagmanager.com/gtag/js?id=UA-131010415-1"></script><script>
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class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/compaction.html">Compaction</a></li><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Stream ingestion</h4><ul><li class="navListItem"><a class="navItem" href="/docs/0.23.0/development/extensions-core/kafka-ingestion.html">Apache Kafka ingestion</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/development/extensions-core/kafka-supervisor-reference.html">Apache Kafka supervisor</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/development/extensions-core/kafka-supervisor-operations.html">Apache Kafka operations</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/development/extensions-core/kinesis-ingestion.html">Amazon Kinesis</a></li></ul></div><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Batch ingestion</h4><ul><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/native-batch.html">Native batch</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/native-batch-simple-task.html">Simple task indexing</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/native-batch-input-sources.html">Input sources</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/native-batch-firehose.html">Firehose</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/hadoop.html">Hadoop-based</a></li></ul></div><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/tasks.html">Task reference</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/ingestion/faq.html">Troubleshooting FAQ</a></li></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Querying<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" 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href="/docs/0.23.0/querying/timeseriesquery.html">Timeseries</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/topnquery.html">TopN</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/groupbyquery.html">GroupBy</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/scan-query.html">Scan</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/searchquery.html">Search</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/timeboundaryquery.html">TimeBoundary</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/segmentmetadataquery.html">SegmentMetadata</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/datasourcemetadataquery.html">DatasourceMetadata</a></li></ul></div><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Native query components</h4><ul><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/filters.html">Filters</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/granularities.html">Granularities</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/dimensionspecs.html">Dimensions</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/aggregations.html">Aggregations</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/post-aggregations.html">Post-aggregations</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/misc/math-expr.html">Expressions</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/having.html">Having filters (groupBy)</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/limitspec.html">Sorting and limiting (groupBy)</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/topnmetricspec.html">Sorting (topN)</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/sorting-orders.html">String comparators</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/querying/virtual-columns.html">Virtual columns</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/development/geo.html">Spatial filters</a></li></ul></div></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Configuration<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><li class="navListItem"><a class="navItem" href="/docs/0.23.0/configuration/index.html">Configuration reference</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/development/extensions.html">Extensions</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/configuration/logging.html">Logging</a></li></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Operations<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/druid-console.html">Web console</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/getting-started.html">Getting started with Apache Druid</a></li><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Security</h4><ul><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/security-overview.html">Security overview</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/security-user-auth.html">User authentication and authorization</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/auth-ldap.html">LDAP auth</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/password-provider.html">Password providers</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/dynamic-config-provider.html">Dynamic Config Providers</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/tls-support.html">TLS support</a></li></ul></div><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Performance tuning</h4><ul><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/basic-cluster-tuning.html">Basic cluster tuning</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/segment-optimization.html">Segment Size Optimization</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/mixed-workloads.html">Mixed workloads</a></li><li class="navListItem"><a 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href="/docs/0.23.0/operations/rolling-updates.html">Rolling updates</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/rule-configuration.html">Retaining or automatically dropping data</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/other-hadoop.html">Working with different versions of Apache Hadoop</a></li><div class="navGroup subNavGroup"><h4 class="navGroupSubcategoryTitle">Misc</h4><ul><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/management-uis.html">Legacy Management UIs</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/dump-segment.html">dump-segment tool</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/reset-cluster.html">reset-cluster tool</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/insert-segment-to-db.html">insert-segment-to-db tool</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/pull-deps.html">pull-deps tool</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/deep-storage-migration.html">Deep storage migration</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/export-metadata.html">Export Metadata Tool</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/metadata-migration.html">Metadata Migration</a></li><li class="navListItem"><a class="navItem" href="/docs/0.23.0/operations/use_sbt_to_build_fat_jar.html">Content for build.sbt</a></li></ul></div></ul></div><div class="navGroup"><h3 class="navGroupCategoryTitle collapsible">Development<span class="arrow"><svg width="24" height="24" viewBox="0 0 24 24"><path fill="#565656" d="M7.41 15.41L12 10.83l4.59 4.58L18 14l-6-6-6 6z"></path><path d="M0 0h24v24H0z" fill="none"></path></svg></span></h3><ul class="hide"><li class="navListItem"><a class="navItem" 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<p>Apache Druid uses <a href="http://zookeeper.apache.org/">Apache ZooKeeper</a> (ZK) for management of current cluster state.</p>
<h2><a class="anchor" aria-hidden="true" id="minimum-zookeeper-versions"></a><a href="#minimum-zookeeper-versions" 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>Minimum ZooKeeper versions</h2>
<p>Apache Druid supports ZooKeeper versions 3.5.x and above.</p>
<blockquote>
<p>Note: Starting with Apache Druid 0.22.0, support for ZooKeeper 3.4.x has been removed</p>
</blockquote>
<h2><a class="anchor" aria-hidden="true" id="zookeeper-operations"></a><a href="#zookeeper-operations" 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 Operations</h2>
<p>The operations that happen over ZK are</p>
<ol>
<li><a href="/docs/0.23.0/design/coordinator.html">Coordinator</a> leader election</li>
<li>Segment &quot;publishing&quot; protocol from <a href="/docs/0.23.0/design/historical.html">Historical</a></li>
<li>Segment load/drop protocol between <a href="/docs/0.23.0/design/coordinator.html">Coordinator</a> and <a href="/docs/0.23.0/design/historical.html">Historical</a></li>
<li><a href="/docs/0.23.0/design/overlord.html">Overlord</a> leader election</li>
<li><a href="/docs/0.23.0/design/overlord.html">Overlord</a> and <a href="/docs/0.23.0/design/middlemanager.html">MiddleManager</a> task management</li>
</ol>
<h2><a class="anchor" aria-hidden="true" id="coordinator-leader-election"></a><a href="#coordinator-leader-election" 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>Coordinator Leader Election</h2>
<p>We use the Curator <a href="https://curator.apache.org/curator-recipes/leader-latch.html">LeaderLatch</a> recipe to perform leader election at path</p>
<pre><code class="hljs">${druid<span class="hljs-selector-class">.zk</span><span class="hljs-selector-class">.paths</span>.coordinatorPath}/_COORDINATOR
</code></pre>
<h2><a class="anchor" aria-hidden="true" id="segment-publishing-protocol-from-historical-and-realtime"></a><a href="#segment-publishing-protocol-from-historical-and-realtime" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Segment &quot;publishing&quot; protocol from Historical and Realtime</h2>
<p>The <code>announcementsPath</code> and <code>servedSegmentsPath</code> are used for this.</p>
<p>All <a href="/docs/0.23.0/design/historical.html">Historical</a> processes publish themselves on the <code>announcementsPath</code>, specifically, they will create an ephemeral znode at</p>
<pre><code class="hljs"><span class="hljs-variable">${druid.zk.paths.announcementsPath}</span>/<span class="hljs-variable">${druid.host}</span>
</code></pre>
<p>Which signifies that they exist. They will also subsequently create a permanent znode at</p>
<pre><code class="hljs"><span class="hljs-variable">${druid.zk.paths.servedSegmentsPath}</span>/<span class="hljs-variable">${druid.host}</span>
</code></pre>
<p>And as they load up segments, they will attach ephemeral znodes that look like</p>
<pre><code class="hljs"><span class="hljs-variable">${druid.zk.paths.servedSegmentsPath}</span><span class="hljs-regexp">/${druid.host}/</span>_segment_identifier_
</code></pre>
<p>Processes like the <a href="/docs/0.23.0/design/coordinator.html">Coordinator</a> and <a href="/docs/0.23.0/design/broker.html">Broker</a> can then watch these paths to see which processes are currently serving which segments.</p>
<h2><a class="anchor" aria-hidden="true" id="segment-loaddrop-protocol-between-coordinator-and-historical"></a><a href="#segment-loaddrop-protocol-between-coordinator-and-historical" aria-hidden="true" class="hash-link"><svg class="hash-link-icon" aria-hidden="true" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path fill-rule="evenodd" d="M4 9h1v1H4c-1.5 0-3-1.69-3-3.5S2.55 3 4 3h4c1.45 0 3 1.69 3 3.5 0 1.41-.91 2.72-2 3.25V8.59c.58-.45 1-1.27 1-2.09C10 5.22 8.98 4 8 4H4c-.98 0-2 1.22-2 2.5S3 9 4 9zm9-3h-1v1h1c1 0 2 1.22 2 2.5S13.98 12 13 12H9c-.98 0-2-1.22-2-2.5 0-.83.42-1.64 1-2.09V6.25c-1.09.53-2 1.84-2 3.25C6 11.31 7.55 13 9 13h4c1.45 0 3-1.69 3-3.5S14.5 6 13 6z"></path></svg></a>Segment load/drop protocol between Coordinator and Historical</h2>
<p>The <code>loadQueuePath</code> is used for this.</p>
<p>When the <a href="/docs/0.23.0/design/coordinator.html">Coordinator</a> decides that a <a href="/docs/0.23.0/design/historical.html">Historical</a> process should load or drop a segment, it writes an ephemeral znode to</p>
<pre><code class="hljs"><span class="hljs-variable">${druid.zk.paths.loadQueuePath}</span><span class="hljs-regexp">/_host_of_historical_process/</span>_segment_identifier
</code></pre>
<p>This znode will contain a payload that indicates to the Historical process what it should do with the given segment. When the Historical process is done with the work, it will delete the znode in order to signify to the Coordinator that it is complete.</p>
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