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+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
+<html>
+<head>
+<title>Traffic Edge Administrator's Guide</title>
+
+<link href="http://trafficserver.apache.org/docs/trunk/admin/getting-started/index.en.html" rel="canonical" />
+<!--#include file="top.html" -->
+
+<h1>Getting Started</h1>
+<p>After you have installed Traffic Server on your system, you can do any of the following:</p>
+<ul>
+ <li><a href="#StartingTrafficEdge">Start Traffic Server</a></li>
+ <li><a href="#StartingTrafficLine">Start Traffic Line</a></li>
+ <li><a href="#StartingTrafficShell">Start Traffic Shell</a></li>
+ <li><a href="#StoppingTrafficEdge">Stop Traffic Server</a></li>
+</ul>
+<h2 id="StartingTrafficEdge">Start Traffic Server</h2>
+<p>To start Traffic Server manually, issue the <code>trafficserver</code> command, passing in the attribute <code>start</code>. This command starts all the processes that work together to process Traffic Server requests as well as manage, control, and monitor the health of the Traffic Server system. </p>
+<h5>To run the <code>trafficserver start</code> command: </h5>
+<ol>
+ <li>Log on to the Traffic Server node as the Traffic Server administrator and navigate to the Traffic Server <code>bin</code> directory. </li>
+ <li>Enter the following command:<br />
+ <code>./start_traffic_server</code></li>
+ <code>./trafficserver start</code>
+</ol>
+<h2 id="StartingTrafficLine">Start Traffic Line</h2>
+
+
+<p>Traffic Line provides a quick way of viewing Traffic Server statistics and configuring the Traffic Server system via command-line interface. To execute individual commands or script multiple commands, refer to <a href="cli.htm">Traffic Line Commands</a>.</p>
+<h5>To start a Traffic Line session: </h5>
+<ol>
+ <li>Log on to a Traffic Server node as the Traffic Server administrator and navigate to the Traffic Server <code>bin</code> directory. <br />
+ Traffic Line commands take the following form:<br /><code>traffic_line <em>-command argument</em></code></li>
+ <li>For a list of <code>traffic_line</code> commands, enter:<br />
+ <code>traffic_line -h</code><br />
+ If the Traffic Server <code>bin</code> directory is not in your path, then prepend the Traffic Line command with <code>./</code> (for example, <code>./traffic_line -h</code>). </li>
+</ol>
+<h2 id="StartingTrafficShell">Start Traffic Shell </h2>
+<p>Traffic Shell is a command-line tool that enables you to monitor and configure Traffic Server; it can be used instead of Traffic Line. Traffic Server provides documentation for Traffic Shell in the form of manual (<code>man</code>) pages. </p>
+<h5>To start Traffic Shell and read an overview <code>man</code> page:</h5>
+<ol>
+ <li>Log on to a Traffic Server node as the Traffic Server administrator and navigate to the Traffic Server <code>bin</code> directory. </li>
+ <li>
+ Enter the following command: <br />
+ <code>./start_traffic_shell</code>
+ </li>
+ <li>Enter the following command to display the <code>traffic_shell</code> overview <code>man</code> page:<br /><code>man traffic_shell</code><br />
+ <br />
+ The <code>man</code> page describes how to use Traffic Shell, how to obtain a list of available commands, and how to obtain documentation about each command.</li>
+</ol>
+<h2 id="StoppingTrafficEdge">Stop Traffic Server </h2>
+<p>To stop Traffic Server, always use the <code>trafficserver</code> command, passing in the attribute <code>stop</code>. This command stops all the Traffic Server processes (<code>traffic_manager</code>, <code>traffic_server</code>, and <code>traffic_cop</code>). Do not manually stop processes, as this can lead to unpredictable results.</p>
+<h5><b>To run the <code>trafficserver stop</code> command:</b></h5>
+<ol>
+ <li>Log on to the node as the Traffic Server administrator and navigate to the Traffic Server <code>bin</code> directory.</li>
+ <li>Enter the following command: <br /> <code>./trafficserver stop</code></li>
+</ol>
+<!--#include file="bottom.html" -->
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+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
+<html>
+<head>
+<title>Traffic Edge Administrator's Guide</title>
+
+<link href="http://trafficserver.apache.org/docs/trunk/admin/hierachical-caching/index.en.html" rel="canonical" />
+<!--#include file="top.html" -->
+
+<h1>Hierarchical Caching</h1>
+<p>Traffic Server can participate in cache hierarchies. Requests not fulfilled in one cache are routed to other regional caches, thereby leveraging the contents and proximity of nearby caches. </p>
+<p>This chapter discusses the following topics: </p>
+<ul>
+<li><a href="#UnderstandingCacheHierarchies">Understanding Cache Hierarchies</a></li>
+<li><a href="#ParentCaching">Parent Caching</a></li>
+<li><a href="#ICPPeering">ICP Peering</a></li>
+</ul>
+<h2 id="UnderstandingCacheHierarchies">Understanding Cache Hierarchies</h2>
+<p>A cache hierarchy consists of cache levels that communicate with each other. Traffic Server supports several types of cache hierarchies. All cache hierarchies recognize the concept of <b>parent</b> and <b>child</b>. A parent cache is a cache higher up in the hierarchy, to which Traffic Server can forward requests. A child cache is a cache for which Traffic Server is a parent. </p>
+<p>Traffic Server supports the following hierarchical caching options: </p>
+<ul>
+ <li><a href="#ParentCaching">Parent Caching</a></li>
+ <li><a href="#ICPPeering">ICP (Internet Cache Protocol) Peering</a></li>
+</ul>
+<h2 id="ParentCaching">Parent Caching</h2>
+<p>If a Traffic Server node cannot find a requested object in its cache, then it searches a parent cache (which itself can search other caches) before finally retrieving the object from the origin server. You can configure a Traffic Server node to use one or more parent caches so that if one parent is unavailable, then another parent is availale to service requests. This is called <a href="#ParentFailover">Parent Failover</a>. Traffic Server will support parent caching for HTTP and HTTPS requests. </p>
+<p><strong>Note:</strong> If you do not want all requests to go to the parent cache, then simply configure Traffic Server to route certain requests (such as requests containing specific URLs) directly to the origin server. SImply set parent proxy rules in <a href="files.htm#parent.config">parent.config</a>.</p>
+<p>The figure below illustrates a simple cache hierarchy with a Traffic Server node configured to use a parent cache. In the following scenario, a client sends a request to a Traffic Server node that is a child in the cache hierarchy (because it's configured to forward missed requests to a parent cache). The request is a cache miss, so Traffic Server then forwards the request to the parent cache, where it is a cache hit. The parent sends a copy of the content to the Traffic Server, where it is cached and then served to the client. Future requests for this content can now be served directly from the Traffic Server cache (until the data is stale or expired).</p>
+<p><img src="images/cachehrc.jpg" width="848" height="572" /></p>
+<blockquote>
+ <p><em><b>Parent caching</b></em></p>
+</blockquote>
+<p><b>Note:</b> If the request is a cache miss on the parent, then the parent retrieves the content from the origin server (or from another cache, depending on the parentâs configuration). The parent caches the content and then sends a copy to Traffic Server (its child), where it is cached and served to the client. </p>
+<h3 id="ParentFailover">Parent Failover</h3>
+<p>Traffic Server supports use of several parent caches. This ensures that if one parent cache is not available, another parent cache can service client requests. </p>
+<p>When you configure your Traffic Server to use more than one parent cache, Traffic Server detects when a parent is not available and sends missed requests to another parent cache. If you specify more than two parent caches, then the order in which the parent caches are queried depends upon the parent proxy rules configured in the <a href="files.htm#parent.config">parent.config</a> configuration file. By default, the parent caches are queried in the order they are listed in the configuration file. </p>
+<h3>Configuring Traffic Server to Use a Parent Cache </h3>
+<p>To configure Traffic Server to use one or more parent caches, you must complete the following steps: </p>
+<ul>
+ <li>Enable the parent caching option. </li>
+ <li>Identify the parent cache you want to use to service missed requests. To use <b>parent failover</b>, you must identify more than one parent cache so that when a parent cache is unavailable, requests are sent to another parent cache.</li>
+</ul>
+<p><strong>Note:</strong> You need to configure the child cache only. No additional configuration is needed for the Traffic Server parent cache. </p>
+<h5>Configure Traffic Server to use a parent cache: </h5>
+<ol>
+ <li>In a text editor, open the <code>records.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Edit the following variable:</li>
+<br />
+<table width="1232" border="1">
+ <tr>
+ <th width="322" scope="col">Variable</th>
+ <th width="894" scope="col">Description</th>
+ </tr>
+ <tr>
+ <td><i><code>proxy.config.http.parent_proxy_routing_enable</code></i></td>
+ <td>Set this variable to 1 to enable the parent caching option.</td>
+ </tr>
+</table>
+<br />
+<li>Save and close the <code>records.config</code> file. </li>
+<li>In a text editor, open the <code>parent.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+<li>Set parent proxy rules to specify the parent cache to which you want missed requests to be forwarded; refer to <a href="files.htm#parent.config">parent.config</a>. <br />
+ The following example configures Traffic Server to route all requests containing the regular expression <code>politics</code> and the path <code>/viewpoint</code> directly to the origin server (bypassing any parent hierarchies): <br /> <code>url_regex=politics prefix=/viewpoint go_direct=true</code><br /><br />
+ The following example configures Traffic Server to direct all missed requests with URLs beginning with <code>mms://host1</code> to the parent cache <code>parent1</code>. If <code>parent1</code> cannot serve the requests, then requests are forwarded to <code>parent2</code>. Because <code>round-robin=true</code>, Traffic Server goes through the parent cache list in a round-robin based on client IP address.
+ <br /><code>dest_host=host1 scheme=mms parent=âparent1;parent2â round-robin=strict</code><br /><br />
+</li>
+<li>Save and close <code>parent.config</code></li>
+<li>Navigate to the Traffic Server <code>bin</code> directory.</li>
+<li>Run the command <code>traffic_line -x</code> to apply the configuration changes.</li>
+</ol>
+<h2 id="ICPPeering">ICP Peering</h2>
+<p>The Internet Cache Protocol (ICP) is used by proxy caches to exchange information about their content. ICP query messages ask other caches if they are storing a particular URL; ICP response messages reply with a hit or miss answer. A cache exchanges ICP messages only with specific <b>ICP peers</b>, which are neighboring caches that can receive ICP messages. An ICP peer can be a <b>sibling cache </b>(which is at the same level in the hierarchy) or a <b>parent cache</b> (which is one level up in the hierarchy). </p>
+<p>If Traffic Server has ICP caching enabled, then it sends ICP queries to its ICP peers when the HTTP request is a cache miss. If there are no hits but parents exist, then a parent is selected using a round-robin policy. If no ICP parents exist, then Traffic Server forwards the request to its HTTP parents. If there are no HTTP parent caches established, then Traffic Server forwards the request to the origin server. </p>
+<p>If Traffic Server receives a hit message from an ICP peer, then Traffic Server sends the HTTP request to that peer. However, it might turn out to be a cache miss because the original HTTP request contains header information that is not communicated by the ICP query. For example, the hit might not be the requested alternate. If an ICP hit turns out to be a miss, then Traffic Server forwards the request to either its HTTP parent caches or to the origin server. </p>
+<p>To configure a Traffic Server node to be part of an ICP cache hierarchy, you must perform the following tasks: </p>
+<ul>
+ <li>Determine if the Traffic Server can receive ICP messages only, or if it can send <i>and</i> receive ICP messages. </li>
+ <li>Determine if Traffic Server can send messages directly to each ICP peer or send a single message on a specified multicast channel. </li>
+ <li>Specify the port used for ICP messages. </li>
+ <li>Set the ICP query timeout. </li>
+ <li>Identify the ICP peers (siblings and parents) with which Traffic Server can communicate.</li>
+</ul>
+<h5>To configure Traffic Server to use an ICP cache hierarchy: </h5>
+<ol>
+ <li>In a text editor, open the <code>records.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Edit the following variables:</li>
+<br />
+<table width="1232" border="1">
+ <tr>
+ <th width="322" scope="col">Variable</th>
+ <th width="894" scope="col">Description</th>
+ </tr>
+ <tr>
+ <td><i><code>proxy.config.icp.enabled</code></i></td>
+ <td>Set this variable to:<br />
+ 0 to disable ICP.<br />
+ 1 to allow Traffic Server to receive ICP queries only.<br />
+ 2 to allow Traffic Server to send and receive ICP queries.</td>
+ </tr>
+ <tr>
+ <td><i><code>proxy.config.icp.icp_port</code></i></td>
+ <td>Set this variable to specify the UDP port that you want to use for ICP messages. The default is 3130. </td>
+ </tr>
+ <tr>
+ <td><i><code>proxy.config.icp.multicast_enabled</code></i></td>
+ <td>Set this variable to:<br />
+ 0 to disable ICP multicast.<br />
+ 1 to enable ICP multicast.</td>
+ </tr>
+ <tr>
+ <td><i><code>proxy.config.icp.query_timeout</code></i></td>
+ <td>Set this variable to specify the timeout used for ICP queries. The default is 2 seconds.</td>
+ </tr>
+</table>
+<br />
+ <li>Save and close <code>records.config</code></li>
+ <li>In a text editor, open the <code>icp.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>For each ICP peer you want to identify, enter a separate rule in the <a href="files.htm#icp.config">icp.config</a> file.</li>
+ <li>Save and close <code>icp.config</code></li>
+ <li>Navigate to the Traffic Server <code>bin</code> directory. </li>
+ <li>Run the command <code>traffic_line -x</code> to apply the configuration changes.</li>
+</ol>
+
+<!--#include file="bottom.html" -->
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+<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
+<html>
+<head>
+<title>Traffic Edge Administrator's Guide</title>
+
+<link href="http://trafficserver.apache.org/docs/trunk/admin/http-proxy-caching/index.en.html" rel="canonical" />
+<!--#include file="top.html" -->
+
+<h1>HTTP Proxy Caching </h1>
+<p>Web proxy caching enables you to store copies of frequently-accessed web objects (such as documents, images, and articles) and then serve this information to users on demand. It improves performance and frees up Internet bandwidth for other tasks. </p>
+<p>This chapter discusses the following topics: </p>
+<ul>
+<li><a href="#UnderstandingHTTPWebProxyCaching">Understanding HTTP Web Proxy Caching</a></li>
+<li><a href="#EnsuringCachedObjectFreshness">Ensuring Cached Object Freshness</a></li>
+<li><a href="#SchedulingUpdatesToLocalCacheContent">Scheduling Updates to Local Cache Content</a></li>
+<li><a href="#PushingContentIntoCache">Pushing Content into the Cache</a></li>
+<li><a href="#PinningContentInCache">Pinning Content in the Cache</a></li>
+<li><a href="#ToCacheOrNotToCache">To Cache or Not to Cache?</a></li>
+<li><a href="#ForcingObjectCaching">Forcing Object Caching</a></li>
+<li><a href="#CachingHTTPAlternates">Caching HTTP Alternates</a></li>
+<li><a href="#UsingCongestionControl">Using Congestion Control</a></li>
+</ul>
+<h2 id="UnderstandingHTTPWebProxyCaching">Understanding HTTP Web Proxy Caching</h2>
+<p>Internet users direct their requests to web servers all over the Internet. A caching server must act as a <b>web proxy server </b>so it can serve those requests. After a web proxy server receives requests for web objects, it either serves the requests or forwards them to the <b>origin server</b> (the web server that contains the original copy of the requested information).
+The Traffic Server proxy supports <b>explicit proxy caching</b>, in which the userâs client software must be configured to send requests directly to the Traffic Server proxy.
+The following overview illustrates how Traffic Server serves a user request.</p>
+<p><strong>Step 1</strong> Traffic Server receives a user request for a web object. </p>
+<p><strong>Step 2</strong> Using the object address, Traffic Server tries to locate the requested object in its object database (<b>cache</b>). </p>
+<p><strong>Step 3</strong> If the object is in the cache, then Traffic Server checks to see if the object is fresh enough to serve. If it is fresh, then Traffic Server serves it to the user as a <b>cache hit</b> (see the figure below).</p>
+<p><img src="images/cache_hit.jpg" width="765" height="399" /></p>
+<blockquote>
+ <p><em><b>A cache hit</b></em> </p>
+</blockquote>
+<p><strong>Step 4</strong> If the data in the cache is stale, then Traffic Server connects to the origin server and checks if the object is still fresh (a <b>revalidation</b>). If it is, then Traffic Server immediately sends the cached copy to the user. </p>
+<p><strong>Step 5</strong> If the object is not in the cache (a <b>cache miss</b>) or if the server indicates the cached copy is no longer valid, then Traffic Server obtains the object from the origin server. The object is then simultaneously streamed to the user and the Traffic Server local cache (see the figure below). Subsequent requests for the object can be served faster because the object is retrieved directly from cache.</p>
+<p><img src="images/cache_miss.jpg" width="886" height="428" /></p>
+<blockquote>
+ <p><em><b>A cache miss</b></em> </p>
+</blockquote>
+<p>Caching is typically more complex than the preceding overview suggests. In particular, the overview does not discuss how Traffic Server ensures freshness, serves correct HTTP alternates, and treats requests for objects that cannot/should not be cached. The following sections discuss these issues in greater detail. </p>
+<h2 id="EnsuringCachedObjectFreshness">Ensuring Cached Object Freshness</h2>
+<p>When Traffic Server receives a request for a web object, it first tries to locate the requested object in its cache. If the object is in cache, then Traffic Server checks to see if the object is fresh enough to serve. For HTTP objects, Traffic Server supports optional author-specified expiration dates. Traffic Server adheres to these expiration dates; otherwise, it picks an expiration date based on how frequently the object is changing and on administrator-chosen freshness guidelines. Objects can also be revalidated by checking with the origin server to see if an object is still fresh. </p>
+<h2><a name="HTTPObjectFreshness"></a>HTTP Object Freshness</h2>
+<p>Traffic Server determines whether an HTTP object in the cache is fresh by:</p>
+<ul>
+ <li><b>Checking the <code>Expires</code> or </b><code><b>max</b></code><b><code>-age</code> header</b><br />
+ Some HTTP objects contain <code>Expires</code> headers or <code>max-age</code> headers that explicitly define how long the object can be cached. Traffic Server compares the current time with the expiration time to determine if the object is still fresh.</li>
+ <li><b>Checking the <code>Last-Modified / Date</code> header</b><br />
+ If an HTTP object has no <code>Expires</code> header or <code>max-age</code> header, then Traffic Server can calculate a freshness limit using the following formula: <br />
+ <code>freshness_limit =(<em>date - last_modified</em>) * 0.10</code> <br />
+ where<code> <i>date</i></code> is the date in the objectâs server response header and <code><i>last_modified </i></code> is the date in the <code>Last-Modified</code> header. If there is no <code>Last-Modified</code> header, then Traffic Server uses the date the object was written to cache. The value <code>0.10</code> (10 percent) can be increased or reduced to better suit your needs (refer to <a href="#ModifyingAgingFactorFreshnessComputations">Modifying the Aging Factor for Freshness Computations</a>).<br />
+ The computed freshness limit is bound by a minimum and maximum value - refer to <a href="#SettingAbsoluteFreshnessLimit">Setting an Absolute Freshness Limit</a> for more information.</li>
+ <li><b>Checking the absolute freshness limit </b><br />
+ For HTTP objects that do not have <code>Expires</code> headers or do not have both <code>Last-Modified</code> and <code>Date</code> headers, Traffic Server uses a maximum and minimum freshness limit (efer to <a href="#SettingAbsoluteFreshnessLimit">Setting an Absolute Freshness Limit</a>).</li>
+ <li><b>Checking revalidate rules in the <code>cache.config</code> file</b><br />
+ Revalidate rules apply freshness limits to specific HTTP objects. You can set freshness limits for objects originating from particular domains or IP addresses, objects with URLs that contain specified regular expressions, objects requested by particular clients, and so on (refer to <a href="files.htm#cache.config">cache.config</a>).</li>
+</ul>
+<h3 id="ModifyingAgingFactorFreshnessComputations">Modifying the Aging Factor for Freshness Computations</h3>
+<p>If an object does not contain any expiration information, then Traffic Server can estimate its freshness from the <code>Last-Modified</code> and <code>Date</code> headers. By default, Traffic Server stores an object for 10% of the time that elapsed since it last changed. You can increase or reduce the percentage according to your needs. </p>
+<h5>To modify the aging factor for freshness computations: </h5>
+<ol>
+ <li>In a text editor, open the <code>records.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Edit the following variable:</li>
+ <table width="100%" border="1">
+ <tr>
+ <th scope="col">Variable</th>
+ <th scope="col">Description</th>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.http.cache.heuristic_lm_factor</i></code></td>
+ <td><p>Set this variable to specify the aging factor for freshness computations. Traffic Server stores an object for this percentage of the time that elapsed since it last changed. <br />
+ The default value is 0.10 (10 percent).</p></td>
+ </tr>
+</table>
+ <li>Save and close the <code>records.config</code> file.</li>
+ <li>Navigate to the Traffic Server <code>bin</code> directory. <br />
+ </li>
+ <li>Run the <code>traffic_line -x</code> command to apply the configuration changes.</li>
+</ol>
+<h3 id="SettingAbsoluteFreshnessLimit">Setting an Absolute Freshness Limit</h3>
+<p>Some objects do not have <code>Expires</code> headers or do not have both <code>Last-Modified</code> and <code>Date</code> headers. To control how long these objects are considered fresh in the cache, specify an <b>absolute freshness limit</b>.</p>
+<h5>To specify an absolute freshness limit: </h5>
+<ol>
+ <li>In a text editor, open the <code>records.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Edit the following variables:</li>
+ <table width="100%" border="1">
+ <tr>
+ <th scope="col">Variable</th>
+ <th scope="col">Description</th>
+ </tr>
+ <tr>
+ <td><i><code>proxy.config.http.cache.heuristic_min_lifetime</code></i></td>
+ <td>Set this variable to specify the minimum amount of time that HTTP objects without an expiration date can remain fresh in the cache before being considered stale. The default value is 3600 seconds (1 hour).</td>
+ </tr>
+ <tr>
+ <td><i><code>proxy.config.http.cache.heuristic_max_lifetime</code></i></td>
+ <td>Set this variable to specify the maximum amount of time that HTTP objects without an expiration date can remain fresh in the cache before being considered stale. The default value is 86400 seconds (1 day).</td>
+ </tr>
+</table>
+ <li>Save and close the <code>records.config</code> file.</li>
+<li>Navigate to the Traffic Server <code>bin</code> directory. <br />
+</li>
+<li>Run the command <code>traffic_line -x</code> to apply the configuration changes. </li>
+</ol>
+<h3>Specifying Header Requirements</h3>
+<p>To further ensure freshness of the objects in the cache, configure Traffic Server to cache only objects with specific headers. By default, Traffic Server caches all objects (including objects with no headers); you should change the default setting only for specialized proxy situations. If you configure Traffic Server to cache only HTTP objects with <code>Expires</code> or <code>max-age</code> headers, then the cache hit rate will be noticeably reduced (since very few objects will have explicit expiration information).</p>
+<h5>To configure Traffic Server to cache objects with specific headers: </h5>
+<ol>
+ <li>In a text editor, open the <code>records.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Edit the following variable:</li>
+ <table width="100%" border="1">
+ <tr>
+ <th scope="col">Variable</th>
+ <th scope="col">Description</th>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.http.cache.required_headers</i></code></td><!-->also described in files.htm -->
+ <td><p>Set this variable to one of the following values:<br />
+ <code>0</code> = no headers required to make document cacheable<br />
+ <code>1</code> = either the <code>Last-Modified</code> header, or an explicit lifetime header, <code> Expires</code> or <code> Cache-Control: max-age</code>, is required<br />
+ <code>2</code> = explicit lifetime is required, <code> Expires</code> or <code> Cache-Control: max-age</code></p></td>
+ </tr>
+</table>
+ <li>Save and close the <code>records.config</code> file. </li>
+ <li>Navigate to the Traffic Server <code>bin</code> directory. </li>
+ <li>Run the command <code>traffic_line -x</code> to apply the configuration changes. </li>
+</ol>
+<h3>Cache-Control Headers </h3>
+<p>Even though an object might be fresh in the cache, clients or servers often impose their own constraints that preclude retrieval of the object from the cache. For example, a client might request that a object <i>not</i> be retrieved from a cache, or if it does, then it cannot have been cached for more than 10 minutes. Traffic Server bases the servability of a cached object on <code>Cache-Control</code> headers that appear in both client requests and server responses. The following <code>Cache-Control</code> headers affect whether objects are served from cache: </p>
+ <ul>
+ <li>The <code>no-cache</code> header, sent by clients, tells Traffic Server that it should not to serve any objects directly from the cache; therefore, Traffic Server will always obtain the object from the origin server. You can configure Traffic Server to ignore client <code>no-cache</code> headers - refer to <a href="#NoCacheHeaders">Configuring Traffic Server to Ignore Client no-cache Headers</a> for more information.</li>
+ <li>The <code>max-age</code> header, sent by servers, is compared to the object age. If the age is less than <code>max-age</code>, then the object is fresh and can be served.</li>
+ <li>The <code>min-fresh</code> header, sent by clients, is an <b>acceptable freshness tolerance</b>. This means that the client wants the object to be at least this fresh. If a cached object does not remain fresh at least this long in the future, then it is revalidated. </li>
+ <li>The <code>max-stale</code> header, sent by clients, permits Traffic Server to serve stale objects provided they are not too old. Some browsers might be willing to take slightly stale objects in exchange for improved performance, especially during periods of poor Internet availability. </li>
+ </ul>
+ <p>Traffic Server applies <code>Cache-Control</code> servability criteria after HTTP freshness criteria. For example, an object might be considered fresh but will not be served if its age is greater than its <code>max-age</code>.</p>
+ <h3>Revalidating HTTP Objects </h3>
+ <p>When a client requests an HTTP object that is stale in the cache, Traffic Server revalidates the object. A <b>revalidation</b> is a query to the origin server to check if the object is unchanged. The result of a revalidation is one of the following:</p>
+ <ul>
+ <li>If the object is still fresh, then Traffic Server resets its freshness limit and serves the object. </li>
+ <li>If a new copy of the object is available, then Traffic Server caches the new object (thereby replacing the stale copy) and simultaneously serves the object to the user. </li>
+ <li>If the object no longer exists on the origin server, then Traffic Server does not serve the cached copy. </li>
+ <li>If the origin server does not respond to the revalidation query, then Traffic Server serves the stale object along with a <code>111 Revalidation Failed</code> warning. </li>
+ </ul>
+<p>By default, Traffic Server revalidates a requested HTTP object in the cache if it considers the object to be stale. Traffic Server evaluates object freshness as described in <a href="#HTTPObjectFreshness">HTTP Object Freshness</a>. You can reconfigure how Traffic Server evaluates freshness by selecting one of the following options: </p>
+ <ul>
+ <li>Traffic Server considers all HTTP objects in the cache to be stale: always revalidate HTTP objects in the cache with the origin server.</li>
+ <li>Traffic Server considers all HTTP objects in the cache to be fresh: never revalidate HTTP objects in the cache with the origin server. </li>
+ <li>Traffic Server considers all HTTP objects without <code>Expires</code> or <code>Cache-control</code> headers to be stale: revalidate all HTTP objects without <code>Expires</code> or <code>Cache-Control</code> headers. </li>
+ </ul>
+ <p>To configure how Traffic Server revalidates objects in the cache, you can set specific revalidation rules in the <code>cache.config</code> file (refer to <a href="files.htm#cache.config">cache.config</a>).</p>
+<h5>To configure revalidation options: </h5>
+<ol>
+ <li>In a text editor, open the <code>records.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Edit the following variable: </li>
+ <table width="100%" border="1">
+ <tr>
+ <th scope="col">Variable</th>
+ <th scope="col">Description</th>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.http.cache.when_to_revalidate</i></code></td>
+ <td><p>Set this variable to one of the following values:<br />
+ 0 = Configures Traffic Server to revalidate an HTTP object whenever it is considered stale in the cache. (Traffic Server checks the headers and the freshness limit, if applicable.) This is the default option.<br />
+ 1 = Configures Traffic Server to revalidate HTTP objects that do not contain <code>Expires</code> or <code>Cache-control</code> headers.<br />
+ 2 = Configures Traffic Server to always revalidate HTTP objects; Traffic Server always considers HTTP objects to be stale.<br />
+ 3 = Configures Traffic Server to never revalidate HTTP objects; Traffic Server always considers HTTP objects to be fresh.</p> </td>
+ </tr>
+</table>
+ <li>Save and close the<code> records.config </code>file. </li>
+<li>Navigate to the Traffic Server <code>bin</code> directory. <br />
+</li>
+<li>Run the command <code>traffic_line -x</code> to apply the configuration changes.</li>
+</ol>
+<h2 id="SchedulingUpdatesToLocalCacheContent">Scheduling Updates to Local Cache Content</h2>
+ <p>To further increase performance and to ensure that HTTP objects are fresh in the cache, you can use the <b>Scheduled Update</b> option. This configures Traffic Server to load specific objects into the cache at scheduled times. You might find this especially beneficial when using Traffic Server as a reverse proxy so you can preload content you anticipate will be in demand. </p>
+<p>To use the Scheduled Update option, you must perform the following tasks. </p>
+ <ul>
+ <li>Specify the list of URLs that contain the objects you want to schedule for update, the time the update should take place, and the recursion depth for the URL.</li>
+ <li>Enable the scheduled update option and configure optional retry settings.</li>
+ </ul>
+ <p>Traffic Server uses the information you specify to determine URLs for which it is responsible. For each URL, Traffic Server derives all recursive URLs (if applicable) and then generates a unique URL list. Using this list, Traffic Server initiates an HTTP <code>GET</code> for each unaccessed URL, ensuring that it remains within the user-defined limits for HTTP concurrency at any given time. The system logs the completion of all HTTP <code>GET</code> operations so you can monitor the performance of this feature. </p>
+<p>Traffic Server also provides a <b>Force Immediate Update</b> option that enables you to update URLs immediately without waiting for the specified update time to occur. You can use this option to test your scheduled update configuration (refer to <a href="#ForcingImmediateUpdate">Forcing an Immediate Update</a>). </p>
+<h3>Configuring the Scheduled Update Option </h3>
+ <h5>To configure the scheduled update option, follow the steps below:</h5>
+<ol>
+<li>In a text editor, open the <code>update.config file</code> located in the Traffic Server <code>config</code> directory. </li>
+ <li>Enter a line in the file for each URL you want to update (refer to <a href="files.htm#update.config">update.config</a>). </li>
+ <li>Save and close the <code>update.config</code> file.</li>
+ <li>In a text editor, open the <code>records.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Edit the following variables:</li>
+ <table width="100%" border="1">
+ <tr>
+ <th scope="col">Variable</th>
+ <th scope="col">Description</th>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.update.enabled</i></code></td>
+ <td>Set this variable to 1 to enable the scheduled update option.</td>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.update.retry_count</i></code></td>
+ <td>Set this variable to specify the number of times you want to retry the scheduled update of a URL in the event of failure. The default value is 10.</td>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.update.retry_interval</i></code></td>
+ <td>Set this variable to specify the delay in seconds between each scheduled update retry for a URL in the event of failure. The default value is 2.</td>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.update.concurrent_updates</i></code></td>
+ <td>Set this variable to specify the maximum simultaneous update requests allowed at any point in time. This option prevents the scheduled update process from overburdening the host. The default value is 100.</td>
+ </tr>
+</table>
+ <li>Save and close the <code>records.config</code> file.</li>
+ <li>Navigate to the Traffic Server <code>bin</code> directory. <br />
+</li>
+ <li>Run the command <code>traffic_line -x</code> to apply the configuration changes. </li>
+ </ol>
+<h3 id="ForcingImmediateUpdate">Forcing an Immediate Update </h3>
+ <p>Traffic Server provides a <b>Force Immediate Update</b> option that enables you to immediately verify the URLs listed in the <code>update.config</code> file. The Force Immediate Update option disregards the offset hour and interval set in the <code>update.config</code> file and immediately updates the URLs listed. </p>
+ <p> To configure the Force Immediate Update option, follow the steps below:</p>
+<ol>
+<li>In a text editor, open the <code>records.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Edit the following variable:</li>
+ <table width="100%" border="1">
+ <tr>
+ <th scope="col">Variable</th>
+ <th scope="col">Description</th>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.update.force</i></code></td>
+ <td><p>Set this variable to 1 to enable the Force Immediate Update option.</p> </td>
+ </tr>
+</table>
+ <li>Make sure that the variable <code><i>proxy.config.update.enabled</i></code> is set to 1. </li>
+ <li>Save and close the <code>records.config</code> file. </li>
+ <li>Navigate to the Traffic Server <code>bin</code> directory.<br />
+</li>
+ <li>Run the <code>command traffic_line -x</code> to apply the configuration changes. </li>
+ </ol>
+<p><strong>IMPORTANT: </strong>When you enable the Force Immediate Update option, Traffic Server continually updates the URLs specified in the <code>update.config</code> file until you disable the option. To disable the Force Immediate Update option, set the variable <code><i>proxy.config.update.force</i></code> to <code>0</code> (zero).</p>
+ <h2><a name="PushingContentIntoCache"></a>Pushing Content into the Cache</h2>
+ <p>Traffic Server supports the HTTP <code>PUSH</code> method of content delivery. Using HTTP <code>PUSH</code>, you can deliver content directly into the cache without user requests. </p>
+ <h3>Configuring Traffic Server to Accept PUSH Requests </h3>
+ <p>Before you can deliver content into your cache using HTTP <code>PUSH</code>, you must configure Traffic Server to accept <code>PUSH</code> requests.</p>
+<h5>To configure Traffic Server to accept <code>PUSH</code> requests: </h5>
+<ol>
+ <li>In a text editor, open the <code>filter.config</code> file located in the Traffic Server config directory. </li>
+ <li>Add the following filter rules to the file to ensure that only certain IP addresses can deliver <code>PUSH</code> requests to the cache: <br />
+<code>domain=. src_ip=<em>ipaddress</em> method=PUSH action=allow <br />domain=. method=PUSH action=deny </code> <br />
+ where <code><em>ipaddress</em></code> is the IP address of the host or range of IP addresses of the hosts from which Traffic Server accepts PUSH requests.
+
+ </li>
+ <li>Save and close the <code>filter.config</code> file. </li>
+ <li>In a text editor, open the <code>records.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Edit the following variable:</li>
+ <table width="100%" border="1">
+ <tr>
+ <th scope="col">Variable</th>
+ <th scope="col">Description</th>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.http.push_method_enabled</i></code></td>
+ <td><p>Set this variable to 1 to enable Traffic Server to accept PUSH requests.</p> </td>
+ </tr>
+</table>
+ <li>Save and close the <code>records.config</code> file. </li>
+ <li>Navigate to the Traffic Server <code>bin</code> directory. </li>
+ <li>Run the command <code>traffic_line -x</code> to apply the configuration changes. </li>
+ </ol>
+<h3>Understanding HTTP PUSH</h3>
+ <p><code>PUSH</code> uses the HTTP 1.1 message format. The body of a <code>PUSH</code> request contains the response header and response body that you want to place in the cache. The following is an example of a <code>PUSH</code> request: </p>
+ <pre>PUSH http://www.company.com HTTP/1.0 <br />Content-length: 84</pre>
+
+<pre>HTTP/1.0 200 OK <br />Content-type: text/html <br />Content-length: 17</pre>
+
+
+<pre><HTML> <br />a <br /></HTML> </pre>
+ <p><strong>IMPORTANT: </strong>Your header must include <code>Content-length</code>; <code>Content-length</code> must include both <code>header</code> and <code>body byte count</code>.</p>
+<h2 id="PinningContentInCache">Pinning Content in the Cache</h2>
+ <p>The <b>Cache Pinning Option</b> configures Traffic Server to keep certain HTTP objects in the cache for a specified time. You can use this option to ensure that the most popular objects are in cache when needed and to prevent Traffic Server from deleting important objects. Traffic Server observes <code>Cache-Control</code> headers and pins an object in the cache only if it is indeed cacheable.</p>
+<h5>To set cache pinning rules and enable Cache Pinning: </h5>
+<ol>
+ <li>In a text editor, open the <code>cache.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Add a rule in the file for each URL you want Traffic Server to pin in the cache, as shown below. <br />
+ <code>url_regex=<em>URL</em> pin-in-cache=12h </code> <br />
+ where <code><em>URL</em></code> is the URL you want Traffic Server to pin in the cache. The time format can be <code>d</code> for days, <code>h</code> for hours (as shown), <code>m</code> for minutes, and <code>s</code> for seconds. You can also use mixed units: for example, <code>1h15m20s</code>. You can add secondary specifiers (such as prefix and suffix) to the rule (refer to <a href="files.htm#cache.config">cache.config</a> for more information). </li>
+ <li>Save and close the <code>cache.config</code> file. </li>
+ <li>In a text editor, open the <code>records.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Edit the following variable:</li>
+ <table width="100%" border="1">
+ <tr>
+ <th scope="col">Variable</th>
+ <th scope="col">Description</th>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.cache.permit.pinning</i></code></td>
+ <td><p>Set this variable to 1 to enable the cache pinning option.</p> </td>
+ </tr>
+</table>
+ <li>Navigate to the Traffic Server <code>bin</code> directory.<br />
+</li>
+ <li>Run the command <code>traffic_line -x</code> to apply the configuration changes. </li>
+ </ol>
+<h2 id="ToCacheOrNotToCache">To Cache or Not to Cache?</h2>
+ <p>When Traffic Server receives a request for a web object that is not in the cache, it retrieves the object from the origin server and serves it to the client. At the same time, Traffic Server checks if the object is cacheable before storing it in its cache to serve future requests. </p>
+<h2 id="CachingHTTPObjects">Caching HTTP Objects</h2>
+ <p>Traffic Server responds to caching directives from clients and origin servers, as well as directives you specify through configuration options and files. </p>
+ <h3>Client Directives </h3>
+ <p>By default, Traffic Server does <i>not</i> cache objects with the following <b>request</b> <b>headers</b>: </p>
+ <ul>
+ <li><code>Cache-Control: no-store</code> header </li>
+ <li><code>Cache-Control: no-cache</code> header <br />
+ To configure Traffic Server to ignore the <code>Cache-Control: no-cache</code> header, refer to <a href="#NoCacheHeaders">Configuring Traffic Server to Ignore Client no-cache Headers</a>. </li>
+ <li><code>Cookie</code>: header (for text objects) <br />
+ By default, Traffic Server caches objects served in response to requests that contain cookies (unless the object is text). You can configure Traffic Server to not cache cookied content of any type, cache all cookied content, or cache cookied content that is of image type only. For more information, refer to <a href="#CachingCookiedObjects">Caching Cookied Objects</a>.</li>
+ <li><code>Authorization</code>: header </li>
+ </ul>
+<h4 id="NoCacheHeaders">Configuring Traffic Server to Ignore Client no-cache Headers </h4>
+ <p>By default, Traffic Server strictly observes client <code>Cache Control:no-cache</code> directives. If a requested object contains a <code>no-cache</code> header, then Traffic Server forwards the request to the origin server even if it has a fresh copy in cache. You can configure Traffic Server to ignore client <code>no-cache</code> directives such that it ignores <code>no-cache</code> headers from client requests and serves the object from its cache. </p>
+<h5>To configure Traffic Server to ignore client <code>no-cache</code> headers: </h5>
+<ol>
+ <li>In a text editor, open the <code>records.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Edit the following variable:</li>
+ <table width="100%" border="1">
+ <tr>
+ <th scope="col">Variable</th>
+ <th scope="col">Description</th>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.http.cache.ignore_client_no_cache</i></code></td>
+ <td><p>Set this variable to 1 to ignore client requests to bypass the cache.</p> </td>
+ </tr>
+</table>
+ <li>Save and close the <code>records.config</code> file. </li>
+ <li>Navigate to the Traffic Server <code>bin</code> directory. <br />
+</li>
+ <li>Run the command <code>traffic_line -x</code> to apply the configuration changes. </li>
+</ol>
+<h3>Origin Server Directives </h3>
+ <p>By default, Traffic Server does <i>not</i> cache objects with the following <b>response</b> <b>headers</b>: </p>
+ <ul>
+ <li><code>Cache-Control: no-store</code> header </li>
+ <li><code>Cache-Control: private</code> header </li>
+ <li><code>WWW-Authenticate</code>: header <br />
+ To configure Traffic Server to ignore<code> WWW-Authenticate</code> headers, refer to <a href="#ConfiguringTrafficEdgeIgnoreWWWAuthenticateHeaders">Configuring Traffic Server to Ignore WWW-Authenticate Headers</a>. </li>
+ <li><code>Set-Cookie</code>: header </li>
+ <li><code>Cache-Control: no-cache</code> headers <br />
+ To configure Traffic Server to ignore <code>no-cache</code> headers, refer to <a href="#ConfiguringTrafficEdgeIgnoreServerNoCacheHeaders">Configuring Traffic Server to Ignore Server no-cache Headers</a>. </li>
+ <li><code>Expires</code>: header with value of 0 (zero) or a past date </li>
+ </ul>
+ <h4 id="ConfiguringTrafficEdgeIgnoreServerNoCacheHeaders">Configuring Traffic Server to Ignore Server <b>no-cache</b> Headers </h4>
+ <p>By default, Traffic Server strictly observes <code>Cache-Control:no-cache</code> directives. A response from an origin server with a <code>no-cache</code> header is not stored in the cache and any previous copy of the object in the cache is removed. If you configure Traffic Server to ignore <code>no-cache</code> headers, then Traffic Server also ignores <code>no-store</code> headers. The default behavior of observing <code>no-cache</code> directives is appropriate in most cases. </p>
+<h5>To configure Traffic Server to ignore server <code>no-cache</code> headers: </h5>
+<ol>
+ <li>In a text editor, open the <code>records.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Edit the following variable:</li>
+ <table width="100%" border="1">
+ <tr>
+ <th scope="col">Variable</th>
+ <th scope="col">Description</th>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.http.cache.ignore_server_no_cache</i></code></td>
+ <td><p>Set this variable to 1 to ignore server directives to bypass the cache.</p> </td>
+ </tr>
+</table>
+ <li>Save and close the <code>records.config</code> file. </li>
+ <li>Navigate to the Traffic Server <code>bin</code> directory. <br />
+</li>
+ <li>Run the command <code>traffic_line -x</code> to apply the configuration changes. </li>
+ </ol>
+<h4 id="ConfiguringTrafficEdgeIgnoreWWWAuthenticateHeaders">Configuring Traffic Server to Ignore WWW-Authenticate Headers </h4>
+ <p>By default, Traffic Server does not cache objects that contain <code>WWW-Authenticate</code> response headers. The <code>WWW-Authenticate</code> header contains authentication parameters the client uses when preparing the authentication challenge response to an origin server. </p>
+ <p>When you configure Traffic Server to ignore origin server <code>WWW-Authenticate</code> headers, all objects with <code>WWW-Authenticate</code> headers are stored in the cache for future requests. However, the default behavior of not caching objects with <code>WWW-Authenticate</code> headers is appropriate in most cases. Only configure Traffic Server to ignore server <code>WWW-Authenticate</code> headers if you are knowledgeable about HTTP 1.1.</p>
+ <h5>To configure Traffic Server to ignore server <code>WWW-Authenticate</code> headers: </h5>
+<ol>
+ <li>In a text editor, open the <code>records.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Edit the following variable:</li>
+ <table width="100%" border="1">
+ <tr>
+ <th scope="col">Variable</th>
+ <th scope="col">Description</th>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.http.cache.ignore_authentication</i></code></td>
+ <td><p>Set this variable to 1 to cache objects with WWW Authenticate headers.</p> </td>
+ </tr>
+</table>
+ <li>Save and close the <code>records.config</code> file. </li>
+ <li>Navigate to the Traffic Server <code>bin</code> directory. </li>
+ <li>Run the command <code>traffic_line -x</code> to apply the configuration changes. </li>
+ </ol>
+<h3>Configuration Directives </h3>
+ <p>In addition to client and origin server directives, Traffic Server responds to directives you specify through configuration options and files. <br />
+ You can configure Traffic Server to do the following: </p>
+ <ul>
+ <li><em>Not </em>cache any HTTP objects (refer to <a href="#DisablingHTTPObjectCaching">Disabling HTTP Object Caching</a>).</li>
+ <li>Cache <b>dynamic content</b> - that is, objects with URLs that end in <code><b>.asp</b></code> or contain a question mark (<b><code>?</code></b>), semicolon (<code><b>;</b></code>), or <code><b>cgi</b></code>. For more information, refer to <a href="#CachingDynamicContent">Caching Dynamic Content</a>. </li>
+ <li>Cache objects served in response to the <code>Cookie:</code> header (refer to <a href="#CachingCookiedObjects">Caching Cookied Objects)</a>. </li>
+ <li>Observe never-cache rules in the <code>cache.config</code> file (refer to <a href="files.htm#cache.config">cache.config</a>).</li>
+ </ul>
+<h4 id="DisablingHTTPObjectCaching"> Disabling HTTP Object Caching</h4>
+ <p>By default, Traffic Server caches all HTTP objects except those for which you have set never-cache rules in the <code>cache.config</code> file. You can disable HTTP object caching so that all HTTP objects are served directly from the origin server and never cached, as detailed below.</p>
+<h5>To disable HTTP object caching manually: </h5>
+<ol>
+ <li>In a text editor, open the <code>records.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Edit the following variable:</li>
+ <table width="100%" border="1">
+ <tr>
+ <th scope="col">Variable</th>
+ <th scope="col">Description</th>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.http.cache.http</i></code></td>
+ <td><p>Set this variable to 0 (zero) to disable HTTP object caching.</p> </td>
+ </tr>
+</table>
+ <li>Save and close the <code>records.config</code> file. </li>
+ <li>Navigate to the Traffic Server <code>bin</code> directory. </li>
+ <li>Run the command <code>traffic_line -x</code> to apply the configuration changes.</li>
+ </ol>
+<h4 id="CachingDynamicContent"> Caching Dynamic Content </h4>
+ <p>A URL is considered <b>dynamic</b> if it ends in <code><b>.asp</b></code> or contains a question mark (<b><code>?</code></b>), a semicolon (<b><code>;</code></b>), or <code><b>cgi</b></code>. By default, Traffic Server does <em>not</em> cache dynamic content. You can configure Traffic Server to cache dynamic content, although it's recommended for specialized proxy situations only.</p>
+<h5>To configure Traffic Server to cache dynamic content: </h5>
+<ol>
+ <li>In a text editor, open the <code>records.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Edit the following variable:</li>
+ <table width="100%" border="1">
+ <tr>
+ <th scope="col">Variable</th>
+ <th scope="col">Description</th>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.http.cache_urls_that_look_dynamic</i></code></td>
+ <td><p>Set this variable to 1 to cache dynamic content.</p> </td>
+ </tr>
+</table>
+ <li>Save and close the <code>records.config</code> file. </li>
+ <li>Navigate to the Traffic Server <code>bin</code> directory.</li>
+ <li>Run the command <code>traffic_line -x</code> to apply the configuration changes.</li>
+ </ol>
+<h4 id="CachingCookiedObjects"> Caching Cookied Objects </h4>
+ <p>By default, Traffic Server caches objects served in response to requests that contain cookies (unless the object is text). Traffic Server does not cache cookied text content because object headers are stored along with the object, and personalized cookie header values could be saved with the object. With non-text objects, it is unlikely that personalized headers are delivered or used. </p>
+ <p>You can reconfigure Traffic Server to: </p>
+ <ul>
+ <li><i>Not </i> cache cookied content of any type. </li>
+ <li>Cache cookied content that is of image type only. </li>
+ <li>Cache all cookied content regardless of type.</li>
+ </ul>
+<h5>To configure how Traffic Server caches cookied content: </h5>
+<ol>
+ <li>In a text editor, open the <code>records.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Edit the following variable:</li>
+ <table width="100%" border="1">
+ <tr>
+ <th scope="col">Variable</th>
+ <th scope="col">Description</th>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.http.cache.cache_responses_to_cookies</i></code></td>
+ <td><p>Set this variable to specify how Traffic Server caches cookied content: <br />
+ 0 = Do not cache any responses to cookies. <br />
+ 1 = Cache all responses to cookies. <br />
+ 2 = Cache responses to cookies of image type only. <br />
+ 3 = Cache all responses to cookies except text content-types (the default).</p> </td>
+ </tr>
+</table>
+ <li>Save and close the <code>records.config</code> file. </li>
+ <li>Navigate to the Traffic Server <code>bin</code> directory. </li>
+ <li>Run the command <code>traffic_line -x</code> to apply the configuration changes. </li>
+ </ol>
+<h2 id="ForcingObjectCaching">Forcing Object Caching</h2>
+ <p>You can force Traffic Server to cache specific URLs (including dynamic URLs) for a specified duration, regardless of <code>Cache-Control</code> response headers. </p>
+<h5>To force document caching: </h5>
+<ol>
+ <li>In a text editor, open the <code>cache.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Add a rule in the file for each URL you want Traffic Server to force cache, as shown below. <br /> <code>url_regex=<em>URL</em> ttl-in-cache=6h</code> <br />
+ where<code><em> URL</em></code> is the URL you want Traffic Server to force cache. The time format can be <code>d</code> for days, <code>h</code> for hours (as shown), <code>m</code> for minutes, and <code>s</code> for seconds. You can also use mixed units: for example, <code>1h15m20s</code>. In addition, you can add secondary specifiers (for example, prefix and suffix) to the rule (refer to <a href="files.htm#cache.config">cache.config</a>). </li>
+ <li>Save and close the <code>cache.config</code> file. </li>
+ <li>Navigate to the Traffic Server <code>bin</code> directory. </li>
+ <li>Run the command <code>traffic_line -x</code> to apply the configuration changes. </li>
+ </ol>
+<h2 id="CachingHTTPAlternates">Caching HTTP Alternates</h2>
+ <p>Some origin servers answer requests to the same URL with a variety of objects. The content of these objects can vary widely, according to whether a server delivers content for different languages, targets different browsers with different presentation styles, or provides different document formats (HTML, PDF). Different versions of the same object are termed <b>alternates</b> and are cached by Traffic Server based on <code>Vary</code> response headers. You can specify additional request and response headers for specific content types that Traffic Server will identify as alternates for caching. You can also limit the number of alternate versions of an object allowed in the cache. </p>
+<h3>Configuring How Traffic Server Caches Alternates</h3><h5>To configure how Traffic Server caches alternates, follow the steps below:
+</h5>
+<ol>
+ <li>In a text editor, open the <code>records.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Edit the following variables:</li>
+ <table width="100%" border="1">
+ <tr>
+ <th scope="col">Variable</th>
+ <th scope="col">Description</th>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.http.cache.enable_default_vary_headers</i></code></td>
+ <td><p>Set this variable to 1 to cache alternate versions of HTTP objects that do not contain the Vary header.</p> </td>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.http.cache.vary_default_text</i></code></td>
+ <td>Set this variable to specify the HTTP header field on which you want to vary if the request is for text: for example, an HTML document.</td>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.http.cache.vary_default_images</i></code></td>
+ <td>Set this variable to specify the HTTP header field on which you want to vary if the request is for images: for example, a <code>.gif</code> file.</td>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.http.cache.vary_default_other</i></code></td>
+ <td>Set this variable to specify the HTTP header field on which you want to vary if the request is for anything other than text or image.</td>
+ </tr>
+ </table>
+ <p><strong>Note:</strong> If you specify <code>Cookie</code> as the header field on which to vary in the above variables, then make sure that the variable <code><i>proxy.config.http.cache.cache_responses_to_cookies</i></code> is set appropriately. <br/>
+ For example, if you set <code><i>proxy.config.http.cache.cache_responses_to_cookies</i> </code> to 2 (cache responses to cookies of image type only) and set the <code><i>proxy.config.http.cache.vary_default_text</i></code> variable to specify cookie, then alternates by cookie will not apply to text. </p>
+ <li>Save and close the <code>records.config</code> file. </li>
+ <li>Navigate to the Traffic Server <code>bin</code> directory. </li>
+ <li>Run the command <code>traffic_line -x</code> to apply the configuration changes. </li>
+
+</ol>
+<h3>Limiting the Number of Alternates for an Object </h3>
+ <p>You can limit the number of alternates Traffic Server can cache per object (the default is 3). </p>
+<p><strong>IMPORTANT:</strong> Large numbers of alternates can affect Traffic Server cache performance because all alternates have the same URL. Although Traffic Server can look up the URL in the index very quickly, it must scan sequentially through available alternates in the object store.</p>
+<h5>To limit the number of alternates: </h5>
+<ol>
+ <li>In a text editor, open the <code>records.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Edit the following variable:</li>
+ <table width="100%" border="1">
+ <tr>
+ <th scope="col">Variable</th>
+ <th scope="col">Description</th>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.cache.limits.http.max_alts</i></code></td>
+ <td><p>Set this variable to specify the maximum number of alternate versions of an object you want Traffic Server to cache. The default value is three.</p> </td>
+ </tr>
+</table>
+ <li>Save and close the <code>records.config</code> file. </li>
+ <li>Navigate to the Traffic Server <code>bin</code> directory. </li>
+ <li>Run the command <code>traffic_line -x</code> to apply the configuration changes. </li>
+ </ol>
+<h2 id="UsingCongestionControl">Using Congestion Control</h2>
+ <p>The <b>Congestion Control</b> option enables you to configure Traffic Server to stop forwarding HTTP requests to origin servers when they become congested. Traffic Server then sends the client a message to retry the congested origin server later. </p>
+ <p>To use the <b>Congestion Control</b> option, you must perform the following tasks: </p>
+ <ul>
+ <li>Enable the Congestion Control option. </li>
+ <li>Create rules in the <code>congestion.config</code> file to specify: </li>
+ <ul>
+ <li>which origin servers Traffic Server tracks for congestion</li>
+ <li>the timeouts Traffic Server uses, depending on whether a server is congested</li>
+ <li>the page Traffic Server sends to the client when a server becomes congested</li>
+ <li>if Traffic Server tracks the origin servers per IP address or per hostname</li>
+ </ul>
+ </ul>
+ <h5>To enable and configure the Congestion Control option : </h5>
+<ol>
+ <li>In a text editor, open the <code>records.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Edit the following variable:</li>
+ <table width="100%" border="1">
+ <tr>
+ <th scope="col">Variable</th>
+ <th scope="col">Description</th>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.http.congestion_control.enabled</i></code></td>
+ <td><p>Set this variable to 1 to enable the congestion control option.</p> </td>
+ </tr>
+</table>
+ <li>Save and close the <code>records.config</code> file. </li>
+ <li>In a text editor, open the <code>congestion.config</code> file located in the Traffic Server <code>config</code> directory. </li>
+ <li>Enter rules to specify which origin servers are tracked for congestion and the timeout values Traffic Server uses to determine congestion. Refer to <a href="files.htm#congestion.config">congestion.config</a> for the rule format. </li>
+ <li>Save and close the <code>congestion.config</code> file. </li>
+ <li>Navigate to the Traffic Server <code>bin</code> directory. </li>
+ <li>Run the command <code>traffic_line -x</code> to apply the configuration changes. </li>
+</ol>
+
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