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<!DOCTYPE html><html lang="en"><head><meta charSet="utf-8"/><meta http-equiv="X-UA-Compatible" content="IE=edge"/><title>Code Organization · Apache Heron</title><meta name="viewport" content="width=device-width"/><meta name="generator" content="Docusaurus"/><meta name="description" content="&lt;!--"/><meta name="docsearch:version" content="0.20.3-incubating"/><meta name="docsearch:language" content="en"/><meta property="og:title" content="Code Organization · Apache Heron"/><meta property="og:type" content="website"/><meta property="og:url" content="https://heron.apache.org/"/><meta property="og:description" content="&lt;!--"/><meta property="og:image" content="https://heron.apache.org/img/undraw_online.svg"/><meta name="twitter:card" content="summary"/><meta name="twitter:image" content="https://heron.apache.org/img/undraw_tweetstorm.svg"/><link rel="shortcut icon" href="/img/favicon-32x32.png"/><link rel="stylesheet" href="//cdnjs.cloudflare.com/ajax/libs/highlight.js/9.12.0/styles/default.min.css"/><link rel="alternate" type="application/atom+xml" href="https://heron.apache.org/blog/atom.xml" title="Apache Heron Blog ATOM Feed"/><link rel="alternate" type="application/rss+xml" href="https://heron.apache.org/blog/feed.xml" title="Apache Heron Blog RSS Feed"/><script>
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<p>This document contains information about the Heron codebase intended primarily
for developers who want to contribute to Heron. The Heron codebase lives on
<a href="https://github.com/apache/incubator-heron/tree/master">github</a>.</p>
<p>If you're looking for documentation about developing topologies for a Heron
cluster, see <a href="topology-development-topology-api-java">Building Topologies</a> instead.</p>
<h2><a class="anchor" aria-hidden="true" id="languages"></a><a href="#languages" 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>Languages</h2>
<p>The primary programming languages for Heron are C++, Java, and Python.</p>
<ul>
<li><p><strong>C++ 11</strong> is used for most of Heron's core components, including the
<a href="heron-architecture#topology-manager">Topology Manager</a>, and
<a href="heron-architecture#stream-manager">Stream Manager</a>.</p></li>
<li><p><strong>Java 11</strong> is used primarily for Heron's <a href="heron-topology-concepts">topology
API</a>, and <a href="heron-architecture#heron-instance">Heron Instance</a>.
It is currently the only language in which topologies can be written. Instructions can be found
in <a href="../../developers/java/topologies">Building Topologies</a>, while documentation for the Java
API can be found <a href="/api/org/apache/heron/api/topology/package-summary.html">here</a>. Please note that Heron topologies do not require Java 11 and can be written in Java 7 or later.</p></li>
<li><p><strong>Python 2</strong> (specifically 2.7) is used primarily for Heron's <a href="user-manuals-heron-cli">CLI interface</a> and UI components such as <a href="user-manuals-heron-ui">Heron UI</a> and the <a href="user-manuals-heron-tracker-runbook">Heron Tracker</a>.</p></li>
</ul>
<h2><a class="anchor" aria-hidden="true" id="main-tools"></a><a href="#main-tools" 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>Main Tools</h2>
<ul>
<li><p><strong>Build tool</strong> --- Heron uses <a href="http://bazel.io/">Bazel</a> as its build tool.
Information on setting up and using Bazel for Heron can be found in <a href="compiling-overview">Compiling Heron</a>.</p></li>
<li><p><strong>Inter-component communication</strong> --- Heron uses <a href="https://developers.google.com/protocol-buffers/?hl=en">Protocol
Buffers</a> for
communication between components. Most <code>.proto</code> definition files can be found in
<a href="https://github.com/apache/incubator-heron/tree/master/heron/proto"><code>heron/proto</code></a>.</p></li>
<li><p><strong>Cluster coordination</strong> --- Heron relies heavily on ZooKeeper for cluster
coordination for distributed deployment, be it for <a href="schedulers-aurora-cluster">Aurora</a> or for a <a href="extending-heron-scheduler">custom
scheduler</a> that you build. More information on ZooKeeper
components in the codebase can be found in the <a href="#state-management">State
Management</a> section below.</p></li>
</ul>
<h2><a class="anchor" aria-hidden="true" id="common-utilities"></a><a href="#common-utilities" 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>Common Utilities</h2>
<p>The <a href="https://github.com/apache/incubator-heron/tree/master/heron/common"><code>heron/common</code></a> contains a variety of
utilities for each of Heron's languages, including useful constants, file
utilities, networking interfaces, and more.</p>
<h2><a class="anchor" aria-hidden="true" id="cluster-scheduling"></a><a href="#cluster-scheduling" 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>Cluster Scheduling</h2>
<p>Heron supports two cluster schedulers out of the box:
<a href="schedulers-aurora-cluster">Aurora</a> and a <a href="schedulers-local">local
scheduler</a>. The Java code for each of those
schedulers can be found in <a href="https://github.com/apache/incubator-heron/tree/master/heron/schedulers"><code>heron/schedulers</code></a>
, while the underlying scheduler API can be found <a href="/api/org/apache/heron/spi/scheduler/package-summary.html">here</a></p>
<p>Info on custom schedulers can be found in <a href="extending-heron-scheduler">Implementing a Custom
Scheduler</a>; info on the currently available schedulers
can be found in <a href="schedulers-aurora-cluster">Deploying Heron on
Aurora</a> and <a href="schedulers-local">Local
Deployment</a>.</p>
<h2><a class="anchor" aria-hidden="true" id="state-management"></a><a href="#state-management" 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>State Management</h2>
<p>The parts of Heron's codebase related to
<a href="http://zookeeper.apache.org/">ZooKeeper</a> are mostly contained in
<a href="https://github.com/apache/incubator-heron/tree/master/heron/state"><code>heron/state</code></a>. There are ZooKeeper-facing
interfaces for <a href="https://github.com/apache/incubator-heron/tree/master/heron/state/src/cpp">C++</a>,
<a href="https://github.com/apache/incubator-heron/tree/master/heron/state/src/java">Java</a>, and
<a href="https://github.com/apache/incubator-heron/tree/master/heron/state/src/python">Python</a> that are used in a variety of
Heron components.</p>
<h2><a class="anchor" aria-hidden="true" id="topology-components"></a><a href="#topology-components" 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>Topology Components</h2>
<h3><a class="anchor" aria-hidden="true" id="topology-manager"></a><a href="#topology-manager" 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>Topology Manager</h3>
<p>The C++ code for Heron's <a href="heron-architecture#topology-manager">Topology
Manager</a> is written in C++ can be
found in <a href="https://github.com/apache/incubator-heron/tree/master/heron/tmanager"><code>heron/tmanager</code></a>.</p>
<h3><a class="anchor" aria-hidden="true" id="stream-manager"></a><a href="#stream-manager" 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>Stream Manager</h3>
<p>The C++ code for Heron's <a href="heron-architecture#stream-manager">Stream
Manager</a> can be found in
<a href="https://github.com/apache/incubator-heron/tree/master/heron/stmgr"><code>heron/stmgr</code></a>.</p>
<h3><a class="anchor" aria-hidden="true" id="heron-instance"></a><a href="#heron-instance" 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>Heron Instance</h3>
<p>The Java code for <a href="heron-architecture#heron-instance">Heron
instances</a> can be found in
<a href="https://github.com/apache/incubator-heron/tree/master/heron/instance"><code>heron/instance</code></a>.</p>
<h3><a class="anchor" aria-hidden="true" id="metrics-manager"></a><a href="#metrics-manager" 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>Metrics Manager</h3>
<p>The Java code for Heron's <a href="heron-architecture#metrics-manager">Metrics
Manager</a> can be found in
<a href="https://github.com/apache/incubator-heron/tree/master/heron/metricsmgr"><code>heron/metricsmgr</code></a>.</p>
<p>If you'd like to implement your own custom metrics handler (known as a <strong>metrics
sink</strong>), see <a href="extending-heron-metric-sink">Implementing a Custom Metrics Sink</a>.</p>
<h2><a class="anchor" aria-hidden="true" id="developer-apis"></a><a href="#developer-apis" 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>Developer APIs</h2>
<h3><a class="anchor" aria-hidden="true" id="topology-api"></a><a href="#topology-api" 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>Topology API</h3>
<p>Heron's API for writing topologies is written in Java. The code for this API can
be found in <a href="https://github.com/apache/incubator-heron/tree/master/heron/api"><code>heron/api</code></a>.</p>
<p>Documentation for writing topologies can be found in <a href="topology-development-topology-api-java">Building
Topologies</a>, while API documentation can be found
<a href="/api/org/apache/heron/api/topology/package-summary.html">here</a>.</p>
<h3><a class="anchor" aria-hidden="true" id="simulator"></a><a href="#simulator" 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>Simulator</h3>
<p>Heron enables you to run topologies in <a href="guides-simulator-mode"><code>Simulator</code></a>
for debugging purposes.</p>
<p>The Java API for simulator can be found in
<a href="/api/org/apache/heron/simulator/package-summary.html"><code>heron/simulator</code></a>.</p>
<h3><a class="anchor" aria-hidden="true" id="example-topologies"></a><a href="#example-topologies" 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 Topologies</h3>
<p>Heron's codebase includes a wide variety of example
<a href="heron-topology-concepts">topologies</a> built using Heron's topology API for
Java. Those examples can be found in
<a href="https://github.com/apache/incubator-heron/tree/master/heron/examples"><code>heron/examples</code></a>.</p>
<h2><a class="anchor" aria-hidden="true" id="user-interface-components"></a><a href="#user-interface-components" 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>User Interface Components</h2>
<h3><a class="anchor" aria-hidden="true" id="heron-cli"></a><a href="#heron-cli" 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>Heron CLI</h3>
<p>Heron has a tool called <code>heron</code> that is used to both provide a CLI interface
for <a href="user-manuals-heron-cli">managing topologies</a> and to perform much of
the heavy lifting behind assembling physical topologies in your cluster.
The Python code for <code>heron</code> can be found in
<a href="https://github.com/apache/incubator-heron/tree/master/heron/tools/cli"><code>heron/tools/cli</code></a>.</p>
<p>Sample configurations for different Heron schedulers</p>
<ul>
<li><a href="schedulers-local">Local scheduler</a> config can be found in <a href="https://github.com/apache/incubator-heron/tree/master/heron/config/src/yaml/conf/local"><code>heron/config/src/yaml/conf/local</code></a>,</li>
<li><a href="schedulers-aurora-cluster">Aurora scheduler</a> config can be found <a href="{https://github.com/apache/incubator-heron/tree/master/heron/config/src/yaml/conf/aurora"><code>heron/config/src/yaml/conf/aurora</code></a>.</li>
</ul>
<h3><a class="anchor" aria-hidden="true" id="heron-tracker"></a><a href="#heron-tracker" 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>Heron Tracker</h3>
<p>The Python code for the <a href="user-manuals-heron-tracker-runbook">Heron Tracker</a> can be
found in <a href="https://github.com/apache/incubator-heron/tree/master/heron/tools/tracker"><code>heron/tools/tracker</code></a>.</p>
<p>The Tracker is a web server written in Python. It relies on the
<a href="http://www.tornadoweb.org/en/stable/">Tornado</a> framework. You can add new HTTP
routes to the Tracker in
<a href="https://github.com/apache/incubator-heron/tree/master/heron/tools/tracker/src/python/main.py"><code>main.py</code></a> and
corresponding handlers in the
<a href="https://github.com/apache/incubator-heron/tree/master/heron/tools/tracker/src/python/handlers"><code>handlers</code></a> directory.</p>
<h3><a class="anchor" aria-hidden="true" id="heron-ui"></a><a href="#heron-ui" 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>Heron UI</h3>
<p>The Python code for the <a href="user-manuals-heron-ui">Heron UI</a> can be found in
<a href="https://github.com/apache/incubator-heron/tree/master/heron/tools/ui"><code>heron/tools/ui</code></a>.</p>
<p>Like Heron Tracker, Heron UI is a web server written in Python that relies on
the <a href="http://www.tornadoweb.org/en/stable/">Tornado</a> framework. You can add new
HTTP routes to Heron UI in
<a href="https://github.com/apache/incubator-heron/tree/master/heron/web/source/python/main.py"><code>main.py</code></a> and corresponding
handlers in the <a href="https://github.com/apache/incubator-heron/tree/master/heron/web/source/python/handlers"><code>handlers</code></a>
directory.</p>
<h3><a class="anchor" aria-hidden="true" id="heron-shell"></a><a href="#heron-shell" 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>Heron Shell</h3>
<p>The Python code for the <a href="user-manuals-heron-shell">Heron Shell</a> can be
found in <a href="https://github.com/apache/incubator-heron/tree/master/heron/shell"><code>heron/shell</code></a>. The HTTP handlers and
web server are defined in
<a href="https://github.com/apache/incubator-heron/tree/master/heron/shell/src/python/main.py"><code>main.py</code></a> while the HTML,
JavaScript, CSS, and images for the web UI can be found in the
<a href="https://github.com/apache/incubator-heron/tree/master/heron/shell/assets"><code>assets</code></a> directory.</p>
<h2><a class="anchor" aria-hidden="true" id="tests"></a><a href="#tests" 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>Tests</h2>
<p>There are a wide variety of tests for Heron that are scattered throughout the
codebase. For more info see <a href="compiling-running-tests">Testing Heron</a>.</p>
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