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+            <ul>
+            
+                <li class="toctree-l3"><a 
href="#operator-development-guide">Operator Development Guide</a></li>
+                
+            
+                <li class="toctree-l3"><a href="#apache-apex-operators">Apache 
Apex Operators </a></li>
+                
+                    <li><a class="toctree-l4" 
href="#operators-what-in-a-nutshell">Operators - “What” in a 
nutshell</a></li>
+                
+                    <li><a class="toctree-l4" 
href="#operators-how-in-a-nutshell">Operators - “How” in a nutshell</a></li>
+                
+                    <li><a class="toctree-l4" href="#types-of-operators">Types 
of Operators</a></li>
+                
+                    <li><a class="toctree-l4" 
href="#operators-position-in-a-dag">Operators Position in a DAG</a></li>
+                
+                    <li><a class="toctree-l4" href="#ports">Ports</a></li>
+                
+                    <li><a class="toctree-l4" href="#how-operator-works">How 
Operator Works</a></li>
+                
+            
+                <li class="toctree-l3"><a 
href="#developing-custom-operators">Developing Custom Operators </a></li>
+                
+                    <li><a class="toctree-l4" 
href="#about-this-tutorial">About this tutorial</a></li>
+                
+                    <li><a class="toctree-l4" 
href="#introduction">Introduction</a></li>
+                
+                    <li><a class="toctree-l4" href="#design">Design</a></li>
+                
+                    <li><a class="toctree-l4" 
href="#configuration">Configuration</a></li>
+                
+                    <li><a class="toctree-l4" href="#code">Code</a></li>
+                
+            
+                <li class="toctree-l3"><a href="#operator-reference">Operator 
Reference </a></li>
+                
+                    <li><a class="toctree-l4" href="#the-operator-class">The 
Operator Class</a></li>
+                
+                    <li><a class="toctree-l4" 
href="#class-operator-properties">Class (Operator) properties</a></li>
+                
+                    <li><a class="toctree-l4" href="#the-constructor">The 
Constructor</a></li>
+                
+                    <li><a class="toctree-l4" href="#setup-call">Setup 
call</a></li>
+                
+                    <li><a class="toctree-l4" href="#begin-window-call">Begin 
Window call</a></li>
+                
+                    <li><a class="toctree-l4" 
href="#process-tuple-call">Process Tuple call</a></li>
+                
+                    <li><a class="toctree-l4" href="#end-window-call">End 
Window call</a></li>
+                
+                    <li><a class="toctree-l4" href="#teardown-call">Teardown 
call</a></li>
+                
+                    <li><a class="toctree-l4" 
href="#testing-your-operator">Testing your Operator</a></li>
+                
+            
+                <li class="toctree-l3"><a 
href="#malhar-operator-library">Malhar Operator Library</a></li>
+                
+            
+            </ul>
+        
+    </li>
+
+        
+            
+    <li class="toctree-l1 ">
+        <a class="" href="../autometrics/">AutoMetric API</a>
+        
+    </li>
+
+        
+    </ul>
+<li>
+          
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+    <ul class="subnav">
+    <li><span>Operations</span></li>
+
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+        <a class="" href="../dtcli/">dtCli</a>
+        
+    </li>
+
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+        <a class="" href="../security/">Security</a>
+        
+    </li>
+
+        
+    </ul>
+<li>
+          
+            <li>
+    <li class="toctree-l1 ">
+        <a class="" href="../compatibility/">Compatibility</a>
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+    </li>
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+            <div class="section">
+              
+                <h1 id="operator-development-guide">Operator Development 
Guide</h1>
+<p>Operators are basic building blocks of an application built to run on
+Apache Apex platform. An application may consist of one or more
+operators each of which define some logical operation to be done on the
+tuples arriving at the operator. These operators are connected together
+using streams forming a Directed Acyclic Graph (DAG). In other words, a 
streaming
+application is represented by a DAG that consists of operations (called 
operators) and
+data flow (called streams).</p>
+<p>In this document we will discuss details on how an operator works and
+its internals. This document is intended to serve the following purposes</p>
+<ol>
+<li><strong><a href="#apex_operators">Apache Apex Operators</a></strong> - 
Introduction to operator terminology and concepts.</li>
+<li><strong><a href="#writing_custom_operators">Writing Custom 
Operators</a></strong> - Designing, coding and testing new operators from 
scratch.  Includes code examples.</li>
+<li><strong><a href="#operator_reference">Operator Reference</a></strong> - 
Details of operator internals, lifecycle, and best practices and 
optimizations.</li>
+</ol>
+<hr />
+<h1 id="apache-apex-operators">Apache Apex Operators <a 
name="apex_operators"></a></h1>
+<h2 id="operators-what-in-a-nutshell">Operators - “What” in a nutshell</h2>
+<p>Operators are independent units of logical operations which can
+contribute in executing the business logic of a use case. For example,
+in an ETL workflow, a filtering operation can be represented by a single
+operator. This filtering operator will be responsible for doing just one
+task in the ETL pipeline, i.e. filter incoming tuples. Operators do not
+impose any restrictions on what can or cannot be done as part of a
+operator. An operator may as well contain the entire business logic.
+However, it is recommended, that the operators are light weight
+independent tasks, in
+order to take advantage of the distributed framework that Apache Apex
+provides. The structure of a streaming application shares resemblance
+with the way CPU pipelining works. CPU pipelining breaks down the
+computation engine into different stages viz. instruction fetch,
+instruction decode, etc. so that each of them can perform their task on
+different instructions
+parallely. Similarly,
+Apache Apex APIs allow the user to break down their tasks into different
+stages so that all of the tasks can be executed on different tuples
+parallely.</p>
+<p><img alt="" src="../images/operator/image05.png" /></p>
+<h2 id="operators-how-in-a-nutshell">Operators - “How” in a nutshell</h2>
+<p>An Apache Apex application runs as a YARN application. Hence, each of
+the operators that the application DAG contains, runs in one of the
+containers provisioned by YARN. Further, Apache Apex exposes APIs to
+allow the user to request bundling multiple operators in a single node,
+a single container or even a single thread. We shall look at these calls
+in the reference sections [cite reference sections]. For now, consider
+an operator as some piece of code that runs on some machine of a YARN
+cluster.</p>
+<h2 id="types-of-operators">Types of Operators</h2>
+<p>An operator works on one tuple at a time. These tuples may be supplied
+by other operators in the application or by external sources,
+such as a database or a message bus. Similarly, after the tuples are
+processed, these may be passed on to other operators, or stored into an 
external system. 
+Therea are 3 type of operators based on function: </p>
+<ol>
+<li><strong>Input Adapter</strong> - This is one of the starting points in
+    the application DAG and is responsible for getting tuples from an
+    external system. At the same time, such data may also be generated
+    by the operator itself, without interacting with the outside
+    world. These input tuples will form the initial universe of
+    data that the application works on.</li>
+<li><strong>Generic Operator</strong> - This type of operator accepts input 
tuples from
+    the previous operators and passes them on to the following operators
+    in the DAG.</li>
+<li><strong>Output Adapter</strong> - This is one of the ending points in the 
application
+    DAG and is responsible for writing the data out to some external
+    system.</li>
+</ol>
+<p>Note: There can be multiple operators of all types in an application
+DAG.</p>
+<h2 id="operators-position-in-a-dag">Operators Position in a DAG</h2>
+<p>We may refer to operators depending on their position with respect to
+one another. For any operator opr (see image below), there are two types of 
operators.</p>
+<ol>
+<li><strong>Upstream operators</strong> - These are the operators from which 
there is a
+    directed path to opr in the application DAG.</li>
+<li><strong>Downstream operators</strong> - These are the operators to which 
there is a
+    directed path from opr in the application DAG.</li>
+</ol>
+<p>Note that there are no cycles formed in the application DAG.</p>
+<p><img alt="" src="../images/operator/image00.png" /></p>
+<h2 id="ports">Ports</h2>
+<p>Operators in a DAG are connected together via directed flows
+called streams. Each stream has end-points located on the operators
+called ports. Therea are 2 types of ports.</p>
+<ol>
+<li><strong>Input Port</strong> - This is a port through which an operator 
accepts input
+    tuples from an upstream operator.</li>
+<li><strong>Output port</strong> - This is a port through which an operator 
passes on the
+    processed data to downstream operators.</li>
+</ol>
+<p>Looking at the number of input ports, an Input Adapter is an operator
+with no input ports, a Generic operator has both input and output ports,
+while an Output Adapter has no output ports. At the same time, note that
+an operator may act as an Input Adapter while at the same time have an
+input port. In such cases, the operator is getting data from two
+different sources, viz. the input stream from the input port and an
+external source.</p>
+<p><img alt="" src="../images/operator/image02.png" /></p>
+<hr />
+<h2 id="how-operator-works">How Operator Works</h2>
+<p>An operator passes through various stages during its lifetime. Each
+stage is an API call that the Streaming Application Master makes for an
+operator.  The following figure illustrates the stages through which an
+operator passes.</p>
+<p><img alt="" src="../images/operator/image01.png" /></p>
+<ul>
+<li>The <em>setup()</em> call initializes the operator and prepares itself to
+    start processing tuples.</li>
+<li>The <em>beginWindow()</em> call marks the beginning of an application 
window
+    and allows for any processing to be done before a window starts.</li>
+<li>The <em>process()</em> call belongs to the <em>InputPort</em> and gets 
triggered when
+    any tuple arrives at the Input port of the operator. This call is
+    specific only to Generic and Output adapters, since Input Adapters
+    do not have an input port. This is made for all the tuples at the
+    input port until the end window marker tuple is received on the
+    input port.</li>
+<li>The <em>emitTuples()</em> is the counterpart of <em>process()</em> call 
for Input
+    Adapters.
+    This call is used by Input adapters to emit any tuples that are
+    fetched from the external systems, or generated by the operator.
+    This method is called continuously until the pre-configured window
+    time is elapsed, at which the end window marker tuple is sent out on
+    the output port.</li>
+<li>The <em>endWindow()</em> call marks the end of the window and allows for 
any
+    processing to be done after the window ends.</li>
+<li>The <em>teardown()</em> call is used for gracefully shutting down the
+    operator and releasing any resources held by the operator.</li>
+</ul>
+<h1 id="developing-custom-operators">Developing Custom Operators <a 
name="writing_custom_operators"></a></h1>
+<h2 id="about-this-tutorial">About this tutorial</h2>
+<p>This tutorial will guide the user towards developing a operator from
+scratch. It includes all aspects of writing an operator including
+design, code and unit testing.</p>
+<h2 id="introduction">Introduction</h2>
+<p>In this tutorial, we will design and write, from scratch, an operator
+called Word Count. This operator will accept tuples of type String,
+count the number of occurrences for each word appearing in the tuple and
+send out the updated counts for all the words encountered in the tuple.
+Further, the operator will also accept a file path on HDFS which will
+contain the stop-words which need to be ignored when counting
+occurrences.</p>
+<h2 id="design">Design</h2>
+<p>Design of the operator must be finalized before starting to write an
+operator. Many aspects including the functionality, the data sources,
+the types involved etc. need to be first finalized before writing the
+operator. Let us dive into each of these while considering the Word
+Count operator.</p>
+<h3 id="functionality">Functionality</h3>
+<p>We can define the scope of operator functionality using the following
+tasks:</p>
+<ol>
+<li>Parse the input tuple to identify the words in the tuple</li>
+<li>Identify the stop-words in the tuple by looking up the stop-word
+    file as configured</li>
+<li>For each non-stop-word in the tuple, count the occurrences in that
+    tuple and add it to a global counts</li>
+</ol>
+<p>Let’s consider an example. Suppose we have the following tuples flow
+into the Word Count operator.</p>
+<ol>
+<li><em>Humpty dumpty sat on a wall</em></li>
+<li><em>Humpty dumpty had a great fall</em></li>
+</ol>
+<p>Initially counts for all words is 0. Once the first tuple is processed,
+the counts that must be emitted are:</p>
+<pre><code class="java">humpty - 1
+dumpty - 1
+sat - 1
+wall - 1
+</code></pre>
+
+<p>Note that we are ignoring the stop-words, “on” and “a” in this case.
+Also note that as a rule, we’ll ignore the case of the words when
+counting occurrences.</p>
+<p>Similarly, after the second tuple is processed, the counts that must be
+emitted are:</p>
+<pre><code class="java">humpty - 2
+dumpty - 2
+great - 1
+fall - 1
+</code></pre>
+
+<p>Again, we ignore the words <em>“had”</em> and <em>“a”</em> since 
these are stop-words.</p>
+<p>Note that the most recent count for any word is correct count for that
+word. In other words, any new output for a word, invalidated all the
+previous counts for that word.</p>
+<h3 id="inputs">Inputs</h3>
+<p>As seen from the example above, the following inputs are expected for
+the operator:</p>
+<ol>
+<li>Input stream whose tuple type is String</li>
+<li>Input HDFS file path, pointing to a file containing stop-words</li>
+</ol>
+<p>Only one input port is needed. The stop-word file will be small enough
+to be read completely in a single read. In addition this will be a one
+time activity for the lifetime of the operator. This does not need a
+separate input port.</p>
+<p><img alt="" src="../images/operator/image03.png" /></p>
+<h3 id="outputs">Outputs</h3>
+<p>We can define the output for this operator in multiple ways.</p>
+<ol>
+<li>The operator may send out the set of counts for which the counts
+    have changed after processing each tuple.</li>
+<li>Some applications might not need an update after every tuple, but
+    only after a certain time duration.</li>
+</ol>
+<p>Let us try and implement both these options depending on the
+configuration. Let us define a boolean configuration parameter
+<em>“sendPerTuple”</em>. The value of this parameter will indicate whether 
the
+updated counts for words need to be emitted after processing each
+tuple (true) or after a certain time duration (false).</p>
+<p>The type of information the operator will be sending out on the output
+port is the same for all the cases. This will be a <em>&lt; key, value 
&gt;</em> pair,
+where the key is the word while, the value is the latest count for that
+word. This means we just need one output port on which this information
+will go out.</p>
+<p><img alt="" src="../images/operator/image04.png" /></p>
+<h2 id="configuration">Configuration</h2>
+<p>We have the following configuration parameters:</p>
+<ol>
+<li><em>stopWordFilePath</em> - This parameter will store the path to the stop
+    word file on HDFS as configured by the user.</li>
+<li><em>sendPerTuple</em> - This parameter decides whether we send out the
+    updated counts after processing each tuple or at the end of a
+    window. When set to true, the operator will send out the updated
+    counts after each tuple, else it will send at the end of
+    each window.</li>
+</ol>
+<h2 id="code">Code</h2>
+<p>The source code for the tutorial can be found here:</p>
+<p><a 
href="https://github.com/DataTorrent/examples/tree/master/tutorials/operatorTutorial";>https://github.com/DataTorrent/examples/tree/master/tutorials/operatorTutorial</a></p>
+<h1 id="operator-reference">Operator Reference <a 
name="operator_reference"></a></h1>
+<h3 id="the-operator-class">The Operator Class</h3>
+<p>The operator will exist physically as a class which implements the
+Operator interface. This interface will require implementations for the
+following method calls:</p>
+<ul>
+<li>setup(OperatorContext context)</li>
+<li>beginWindow(long windowId)</li>
+<li>endWindow()</li>
+<li>tearDown()</li>
+</ul>
+<p>In order to simplify the creation of an operator, Apache Apex
+library also provides a base class “BaseOperator” which has empty
+implementations for these methods. Please refer to the <a 
href="#apex_operators">Apex Operators</a> section and the
+<a href="#operator_reference">Reference</a> section for details on these.</p>
+<p>We extend the class “BaseOperator” to create our own operator
+“WordCountOperator”.</p>
+<pre><code class="java">public class WordCountOperator extends BaseOperator
+{
+}
+</code></pre>
+
+<h3 id="class-operator-properties">Class (Operator) properties</h3>
+<p>We define the following class variables:</p>
+<ul>
+<li><em>sendPerTuple</em> - Configures the output frequency from the 
operator</li>
+</ul>
+<pre><code class="java">private boolean sendPerTuple = true; // default
+</code></pre>
+
+<ul>
+<li><em>stopWordFilePath</em> - Stores the path to the stop words file on 
HDFS</li>
+</ul>
+<pre><code class="java">private String stopWordFilePath; // no default
+</code></pre>
+
+<ul>
+<li><em>stopWords</em> - Stores the stop words read from the configured 
file</li>
+</ul>
+<pre><code class="java">private transient String[] stopWords;
+</code></pre>
+
+<ul>
+<li><em>globalCounts</em> - A Map which stores the counts of all the words
+    encountered so far. Note that this variable is non transient, which
+    means that this variable is saved as part of the checkpoint and can be 
recovered in event of a crash.</li>
+</ul>
+<pre><code class="java">private Map&lt;String, Long&gt; globalCounts;
+</code></pre>
+
+<ul>
+<li><em>updatedCounts</em> - A Map which stores the counts for only the most
+    recent tuple(s). sendPerTuple configuration determines whether to store 
the most recent or the recent
+    window worth of tuples.</li>
+</ul>
+<pre><code class="java">private transient Map&lt;String, Long&gt; 
updatedCounts;
+</code></pre>
+
+<ul>
+<li><em>input</em> - The input port for the operator. The type of this input 
port
+    is String which means it will only accept tuples of type String. The
+    definition of an input port requires implementation of a method
+    called process(String tuple), which should have the processing logic
+    for the input tuple which  arrives at this input port. We delegate
+    this task to another method called processTuple(String tuple). This
+    helps in keeping the operator classes extensible by overriding the
+    processing logic for the input tuples.</li>
+</ul>
+<pre><code class="java">public transient DefaultInputPort&lt;String&gt; input 
= new    
+DefaultInputPort&lt;String&gt;()
+{
+    @Override
+    public void process(String tuple)
+    {
+        processTuple(tuple);
+    }
+};
+</code></pre>
+
+<ul>
+<li>output - The output port for the operator. The type of this port is
+    Entry &lt; String, Long &gt;, which means the operator will emit &lt; word,
+    count &gt; pairs for the updated counts.</li>
+</ul>
+<pre><code class="java">public transient DefaultOutputPort 
&lt;Entry&lt;String, Long&gt;&gt; output = new
+DefaultOutputPort&lt;Entry&lt;String,Long&gt;&gt;();
+</code></pre>
+
+<h3 id="the-constructor">The Constructor</h3>
+<p>The constructor is the place where we initialize the non-transient data
+structures, since
+constructor is called just once per activation of an operator. With regards to 
Word Count operator, we initialize the globalCounts variable in the 
constructor.</p>
+<pre><code class="java">globalCounts = Maps.newHashMap();
+</code></pre>
+
+<h3 id="setup-call">Setup call</h3>
+<p>The setup method is called only once during an operator lifetime and its 
purpose is to allow 
+the operator to set itself up for processing incoming streams. Transient 
objects in the operator are
+not serialized and checkpointed. Hence, it is essential that such objects 
initialized in the setup call. 
+In case of operator failure, the operator will be redeployed (most likely on a 
different container). The setup method called by the Apache Apex engine allows 
the operator to prepare for execution in the new container.</p>
+<p>The following tasks are executed as part of the setup call:</p>
+<ol>
+<li>Read the stop-word list from HDFS and store it in the
+    stopWords array</li>
+<li>Initialize updatedCounts variable. This will store the updated
+    counts for words in most recent tuples processed by the operator.
+    As a transient variable, the value will be lost when operator fails.</li>
+</ol>
+<h3 id="begin-window-call">Begin Window call</h3>
+<p>The begin window call signals the start of an application window. With 
+regards to Word Count Operator, we are expecting updated counts for the most 
recent window of
+data if the sendPerTuple is set to false. Hence, we clear the updatedCounts 
variable in the begin window
+call and start accumulating the counts till the end window call.</p>
+<h3 id="process-tuple-call">Process Tuple call</h3>
+<p>The processTuple method is called by the process method of the input
+port, input. This method defines the processing logic for the current
+tuple that is received at the input port. As part of this method, we
+identify the words in the current tuple and update the globalCounts and
+the updatedCounts variables. In addition, if the sendPerTuple variable
+is set to true, we also emit the words and corresponding counts in
+updatedCounts to the output port. Note that in this case (sendPerTuple =
+true), we clear the updatedCounts variable in every call to
+processTuple.</p>
+<h3 id="end-window-call">End Window call</h3>
+<p>This call signals the end of an application window. With regards to Word
+Count Operator, we emit the updatedCounts to the output port if the
+sendPerTuple flag is set to false.</p>
+<h3 id="teardown-call">Teardown call</h3>
+<p>This method allows the operator to gracefully shut down itself after
+releasing the resources that it has acquired. With regards to our operator,
+we call the shutDown method which shuts down the operator along with any
+downstream operators.</p>
+<h2 id="testing-your-operator">Testing your Operator</h2>
+<p>As part of testing our operator, we test the following two facets:</p>
+<ol>
+<li>Test output of the operator after processing a single tuple</li>
+<li>Test output of the operator after processing of a window of tuples</li>
+</ol>
+<p>The unit tests for the WordCount operator are available in the class
+WordCountOperatorTest.java. We simulate the behavior of the engine by
+using the test utilities provided by Apache Apex libraries. We simulate
+the setup, beginWindow, process method of the input port and
+endWindow calls and compare the output received at the simulated output
+ports.</p>
+<ol>
+<li>Invoke constructor; non-transients initialized.</li>
+<li>Copy state from checkpoint -- initialized values from step 1 are
+replaced.</li>
+</ol>
+<h1 id="malhar-operator-library">Malhar Operator Library</h1>
+<p>To see the full list of Apex Malhar operators along with related 
documentation, visit <a 
href="https://github.com/apache/incubator-apex-malhar";>Apex Malhar on 
Github</a></p>
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+                <li class="toctree-l3"><a href="#security">Security</a></li>
+                
+                    <li><a class="toctree-l4" 
href="#kerberos-authentication">Kerberos Authentication</a></li>
+                
+                    <li><a class="toctree-l4" 
href="#configuring-security">Configuring security</a></li>
+                
+                    <li><a class="toctree-l4" 
href="#security-architecture">Security architecture</a></li>
+                
+                    <li><a class="toctree-l4" 
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+                
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+                <h1 id="security">Security</h1>
+<p>Applications built on Apex run as native YARN applications on Hadoop. The 
security framework and apparatus in Hadoop apply to the applications. The 
default security mechanism in Hadoop is Kerberos.</p>
+<h2 id="kerberos-authentication">Kerberos Authentication</h2>
+<p>Kerberos is a ticket based authentication system that provides 
authentication in a distributed environment where authentication is needed 
between multiple users, hosts and services. It is the de-facto authentication 
mechanism supported in Hadoop. To use Kerberos authentication, the Hadoop 
installation must first be configured for secure mode with Kerberos. Please 
refer to the administration guide of your Hadoop distribution on how to do 
that. Once Hadoop is configured, there is some configuration needed on Apex 
side as well.</p>
+<h2 id="configuring-security">Configuring security</h2>
+<p>There is Hadoop configuration and CLI configuration. Hadoop configuration 
may be optional.</p>
+<h3 id="hadoop-configuration">Hadoop Configuration</h3>
+<p>An Apex application uses delegation tokens to authenticate with the 
ResourceManager (YARN) and NameNode (HDFS) and these tokens are issued by those 
servers respectively. Since the application is long-running,
+the tokens should be valid for the lifetime of the application. Hadoop has a 
configuration setting for the maximum lifetime of the tokens and they should be 
set to cover the lifetime of the application. There are separate settings for 
ResourceManager and NameNode delegation
+tokens.</p>
+<p>The ResourceManager delegation token max lifetime is specified in 
<code>yarn-site.xml</code> and can be specified as follows for example for a 
lifetime of 1 year</p>
+<pre><code class="xml">&lt;property&gt;
+  &lt;name&gt;yarn.resourcemanager.delegation.token.max-lifetime&lt;/name&gt;
+  &lt;value&gt;31536000000&lt;/value&gt;
+&lt;/property&gt;
+</code></pre>
+
+<p>The NameNode delegation token max lifetime is specified in
+hdfs-site.xml and can be specified as follows for example for a lifetime of 1 
year</p>
+<pre><code class="xml">&lt;property&gt;
+   &lt;name&gt;dfs.namenode.delegation.token.max-lifetime&lt;/name&gt;
+   &lt;value&gt;31536000000&lt;/value&gt;
+ &lt;/property&gt;
+</code></pre>
+
+<h3 id="cli-configuration">CLI Configuration</h3>
+<p>The Apex command line interface is used to launch
+applications along with performing various other operations and administrative 
tasks on the applications.  When Kerberos security is enabled in Hadoop, a 
Kerberos ticket granting ticket (TGT) or the Kerberos credentials of the user 
are needed by the CLI program <code>dtcli</code> to authenticate with Hadoop 
for any operation. Kerberos credentials are composed of a principal and either 
a <em>keytab</em> or a password. For security and operational reasons only 
keytabs are supported in Hadoop and by extension in Apex platform. When user 
credentials are specified, all operations including launching
+application are performed as that user.</p>
+<h4 id="using-kinit">Using kinit</h4>
+<p>A Kerberos ticket granting ticket (TGT) can be obtained by using the 
Kerberos command <code>kinit</code>. Detailed documentation for the command can 
be found online or in man pages. An sample usage of this command is</p>
+<pre><code>kinit -k -t path-tokeytab-file kerberos-principal
+</code></pre>
+<p>If this command is successful, the TGT is obtained, cached and available 
for other programs. The CLI program <code>dtcli</code> can then be started to 
launch applications and perform other operations.</p>
+<h4 id="using-kerberos-credentials">Using Kerberos credentials</h4>
+<p>The CLI program <code>dtcli</code> can also use the Kerberos credentials 
directly without requiring a TGT to be obtained separately. This can be useful 
in batch mode where <code>dtcli</code> is not launched manually and also in 
scenarios where running another program like <code>kinit</code> is not 
feasible.</p>
+<p>The credentials can be specified in the <code>dt-site.xml</code> 
configuration file. If only a single user is launching applications, the global 
<code>dt-site.xml</code> configuration file in the installation folder can be 
used. In a multi-user environment the users can use the 
<code>dt-site.xml</code> file in their
+home directory. The location of this file will be 
<code>$HOME/.dt/dt-site.xml</code>. If this file does not exist, the user can 
create a new one.</p>
+<p>The snippet below shows the how the credentials can be specified in the 
configuration file as properties.</p>
+<pre><code class="xml">&lt;property&gt;
+        &lt;name&gt;dt.authentication.principal&lt;/name&gt;
+        &lt;value&gt;kerberos-principal-of-user&lt;/value&gt;
+&lt;/property&gt;
+&lt;property&gt;
+        &lt;name&gt;dt.authentication.keytab&lt;/name&gt;
+        &lt;value&gt;absolute-path-to-keytab-file&lt;/value&gt;
+&lt;/property&gt;
+</code></pre>
+
+<p>The property <code>dt.authentication.principal</code> specifies the 
Kerberos user principal and <code>dt.authentication.keytab</code> specifies the 
absolute path to the keytab file for the user.</p>
+<p>The subsequent sections talk about how security works in Apex. This 
information is not needed by users but is intended for the inquisitive techical 
audience who want to know how security works.</p>
+<h2 id="security-architecture">Security architecture</h2>
+<p>In this section we will see how security works for applications built on 
Apex. We will look at the different methodologies involved in running the 
applications and in each case we will look into the different components that 
are involved. We will go into the architecture of these components and look at 
the different security mechanisms that are in play.</p>
+<h3 id="application-launch">Application Launch</h3>
+<p>To launch applications in Apache Apex the command line client dtcli can be 
used. The application artifacts such as binaries and properties are supplied as 
an application package. The client, during the various steps involved to launch 
the application needs to communicate with both the Resource Manager and the 
Name Node. The Resource Manager communication involves the client asking for 
new resources to run the application master and start the application launch 
process. The steps along with sample Java code are described in Writing YARN 
Applications. The Name Node communication includes the application artifacts 
being copied to HDFS so that they are available across the cluster for 
launching the different application containers.</p>
+<p>In secure mode, the communications with both Resource Manager and Name Node 
requires authentication and the mechanism is Kerberos. Below is an illustration 
showing this.</p>
+<p><img alt="" src="../images/security/image02.png" />        </p>
+<p>The client dtcli supports Kerberos authentication and will automatically 
enable it in a secure environment. To authenticate, some Kerberos configuration 
namely the Kerberos credentials, are needed by the client. There are two 
parameters, the Kerberos principal and keytab to use for the client. These can 
be specified in the dt-site.xml configuration file. The properties are shown 
below</p>
+<pre><code>    &lt;property&gt;
+            &lt;name&gt;dt.authentication.principal&lt;/name&gt;
+            &lt;value&gt;kerberos-principal-of-user&lt;/value&gt;
+    &lt;/property&gt;
+    &lt;property&gt;
+            &lt;name&gt;dt.authentication.keytab&lt;/name&gt;
+            &lt;value&gt;absolute-path-to-keytab-file&lt;/value&gt;
+    &lt;/property&gt;
+</code></pre>
+<p>Refer to document Operation and Installation Guide section Multi Tenancy 
and Security subsection CLI Configuration in the documentation for more 
information. The document can also be accessed here client configuration</p>
+<p>There is another important functionality that is performed by the client 
and that is to retrieve what are called delegation tokens from the Resource 
Manager and Name Node to seed the application master container that is to be 
launched. This is detailed in the next section. </p>
+<h3 id="runtime-security">Runtime Security</h3>
+<p>When the application is completely up and running, there are different 
components of the application running as separate processes possibly on 
different nodes in the cluster as it is a distributed application. These 
components interactwould be interacting with each other and the Hadoop 
services. In secure mode, all these interactions have to be authenticated 
before they can be successfully processed. The interactions are illustrated 
below in a diagram to give a complete overview. Each of them is explained in 
subsequent sections.</p>
+<p><img alt="" src="../images/security/image00.png" /></p>
+<h4 id="stram-and-hadoop">STRAM and Hadoop</h4>
+<p>Every Apache Apex application has a master process akin to any YARN 
application. In our case it is called STRAM (Streaming Application Master). It 
is a master process that runs in its own container and manages the different 
distributed components of the application. Among other tasks it requests 
Resource Manager for new resources as they are needed and gives back resources 
that are no longer needed. STRAM also needs to communicate with Name Node from 
time-to-time to access the persistent HDFS file system. </p>
+<p>In secure mode, STRAM has to authenticate with both Resource Manager and 
Name Node before it can send any requests and this is achieved using Delegation 
Tokens. Since STRAM runs as a managed application master, it runs in a Hadoop 
container. This container could have been allocated on any node based on what 
resources were available. Since there is no fixed node where STRAM runs, it 
does not have Kerberos credentials. Unlike launch client dtcli, it cannot 
authenticate with Hadoop services Resource Manager and Name Node using 
Kerberos. Instead, Delegation Tokens are used for authentication.</p>
+<h5 id="delegation-tokens">Delegation Tokens</h5>
+<p>Delegation tokens are tokens that are dynamically issued by the source and 
clients use them to authenticate with the source. The source stores the 
delegation tokens it has issued in a cache and checks the delegation token sent 
by a client against the cache. If a match is found, the authentication is 
successful else it fails. This is the second mode of authentication in secure 
Hadoop after Kerberos. More details can be found in the Hadoop security design 
document. In this case the delegation tokens are issued by Resource Manager and 
Name Node. STRAM would use these tokens to authenticate with them. But how does 
it get them in the first place? This is where the launch client dtcli comes 
in.</p>
+<p>The client dtcli, since it possesses Kerberos credentials as explained in 
the Application Launch section, is able to authenticate with Resource Manager 
and Name Node using Kerberos. It then requests for delegation tokens over the 
Kerberos authenticated connection. The servers return the delegation tokens in 
the response payload. The client in requesting the resource manager for the 
start of the application master container for STRAM seeds it with these tokens 
so that when STRAM starts it has these tokens. It can then use these tokens to 
authenticate with the Hadoop services.</p>
+<h4 id="streaming-container">Streaming Container</h4>
+<p>A streaming container is a process that runs a part of the application 
business logic. It is a container deployed on a node in the cluster. The part 
of business logic is implemented in what we call an operator. Multiple 
operators connected together make up the complete application and hence there 
are multiple streaming containers in an application. The streaming containers 
have different types of communications going on as illustrated in the diagram 
above. They are described below.</p>
+<h5 id="stram-delegation-token">STRAM Delegation Token</h5>
+<p>The streaming containers periodically communicate with the application 
master STRAM. In the communication they send what are called heartbeats with 
information such as statistics and receive commands from STRAM such as 
deployment or un-deployment of operators, changing properties of operators etc. 
In secure mode, this communication cannot just occur without any 
authentication. To facilitate this authentication special tokens called STRAM 
Delegation Tokens are used. These tokens are created and managed by STRAM. When 
a new streaming container is being started, since STRAM is the one negotiating 
resources from Resource Manager for the container and requesting to start the 
container, it seeds the container with the STRAM delegation token necessary to 
communicate with it. Thus, a streaming container has the STRAM delegation token 
to successfully authenticate and communicate with STRAM.</p>
+<h5 id="buffer-server-token">Buffer Server Token</h5>
+<p>As mentioned earlier an operator implements a piece of the business logic 
of the application and multiple operators together complete the application. In 
creating the application the operators are assembled together in a direct 
acyclic graph, a pipeline, with output of operators becoming the input for 
other operators. At runtime the stream containers hosting the operators are 
connected to each other and sending data to each other. In secure mode these 
connections should be authenticated too, more importantly than others, as they 
are involved in transferring application data.</p>
+<p>When operators are running there will be effective processing rate 
differences between them due to intrinsic reasons such as operator logic or 
external reasons such as different resource availability of CPU, memory, 
network bandwidth etc. as the operators are running in different containers. To 
maximize performance and utilization the data flow is handled asynchronous to 
the regular operator function and a buffer is used to intermediately store the 
data that is being produced by the operator. This buffered data is served by a 
buffer server over the network connection to the downstream streaming container 
containing the operator that is supposed to receive the data from this 
operator. This connection is secured by a token called the buffer server token. 
These tokens are also generated and seeded by STRAM when the streaming 
containers are deployed and started and it uses different tokens for different 
buffer servers to have better security.</p>
+<h5 id="namenode-delegation-token">NameNode Delegation Token</h5>
+<p>Like STRAM, streaming containers also need to communicate with NameNode to 
use HDFS persistence for reasons such as saving the state of the operators. In 
secure mode they also use NameNode delegation tokens for authentication. These 
tokens are also seeded by STRAM for the streaming containers.</p>
+<h2 id="conclusion">Conclusion</h2>
+<p>We looked at the different security requirements for distributed 
applications when they run in a secure Hadoop environment and looked at how 
Apex solves this.</p>
+              
+            </div>
+          </div>
+          <footer>
+  
+    <div class="rst-footer-buttons" role="navigation" aria-label="footer 
navigation">
+      
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+      
+    </div>
+  
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+    <span class="rst-current-version" data-toggle="rst-current-version">
+      
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+        <span><a href="../dtcli/" style="color: #fcfcfc;">&laquo; 
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+        <span style="margin-left: 15px"><a href="../compatibility/" 
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@@ -0,0 +1,70 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9";>
+
+    
+    <url>
+     <loc>/</loc>
+     <lastmod>2016-04-07</lastmod>
+     <changefreq>daily</changefreq>
+    </url>
+    
+
+    
+        
+    <url>
+     <loc>/apex_development_setup/</loc>
+     <lastmod>2016-04-07</lastmod>
+     <changefreq>daily</changefreq>
+    </url>
+        
+    <url>
+     <loc>/application_development/</loc>
+     <lastmod>2016-04-07</lastmod>
+     <changefreq>daily</changefreq>
+    </url>
+        
+    <url>
+     <loc>/application_packages/</loc>
+     <lastmod>2016-04-07</lastmod>
+     <changefreq>daily</changefreq>
+    </url>
+        
+    <url>
+     <loc>/operator_development/</loc>
+     <lastmod>2016-04-07</lastmod>
+     <changefreq>daily</changefreq>
+    </url>
+        
+    <url>
+     <loc>/autometrics/</loc>
+     <lastmod>2016-04-07</lastmod>
+     <changefreq>daily</changefreq>
+    </url>
+        
+    
+
+    
+        
+    <url>
+     <loc>/dtcli/</loc>
+     <lastmod>2016-04-07</lastmod>
+     <changefreq>daily</changefreq>
+    </url>
+        
+    <url>
+     <loc>/security/</loc>
+     <lastmod>2016-04-07</lastmod>
+     <changefreq>daily</changefreq>
+    </url>
+        
+    
+
+    
+    <url>
+     <loc>/compatibility/</loc>
+     <lastmod>2016-04-07</lastmod>
+     <changefreq>daily</changefreq>
+    </url>
+    
+
+</urlset>
\ No newline at end of file

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+++ b/docs/apex-3.2/toc.html
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+{% if nav_item.children %}
+    <ul class="subnav">
+    <li><span>{{ nav_item.title }}</span></li>
+
+        {% for nav_item in nav_item.children %}
+            {% include 'toc.html' %}
+        {% endfor %}
+    </ul>
+{% else %}
+    <li class="toctree-l1 {% if nav_item.active%}current{%endif%}">
+        <a class="{% if nav_item.active%}current{%endif%}" href="{{ 
nav_item.url }}">{{ nav_item.title }}</a>
+        {% if nav_item == current_page %}
+            <ul>
+            {% for toc_item in toc %}
+                <li class="toctree-l3"><a href="{{ toc_item.url }}">{{ 
toc_item.title }}</a></li>
+                {% for toc_item in toc_item.children %}
+                    <li><a class="toctree-l4" href="{{ toc_item.url }}">{{ 
toc_item.title }}</a></li>
+                {% endfor %}
+            {% endfor %}
+            </ul>
+        {% endif %}
+    </li>
+{% endif %}

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+++ b/docs/apex-3.2/versions.html
@@ -0,0 +1,15 @@
+<div class="rst-versions" role="note" style="cursor: pointer">
+    <span class="rst-current-version" data-toggle="rst-current-version">
+      {% if repo_name == 'GitHub' %}
+          <a href="{{ repo_url }}" class="icon icon-github" style="float: 
left; color: #fcfcfc"> GitHub</a>
+      {% elif repo_name == 'Bitbucket' %}
+          <a href="{{ repo_url }}" class="icon icon-bitbucket" style="float: 
left; color: #fcfcfc"> BitBucket</a>
+      {% endif %}
+      {% if previous_page %}
+        <span><a href="{{ previous_page.url }}" style="color: 
#fcfcfc;">&laquo; Previous</a></span>
+      {% endif %}
+      {% if next_page %}
+        <span style="margin-left: 15px"><a href="{{ next_page.url }}" 
style="color: #fcfcfc">Next &raquo;</a></span>
+      {% endif %}
+    </span>
+</div>

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