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Posted to commits@trafficserver.apache.org by di...@apache.org on 2010/01/12 22:16:49 UTC
svn commit: r898518 - /incubator/trafficserver/site/trunk/docs/admin/http.htm
Author: dianes
Date: Tue Jan 12 21:16:45 2010
New Revision: 898518
URL: http://svn.apache.org/viewvc?rev=898518&view=rev
Log:
Fixed typos, grammar, formatting previously overlooked in first draft.
Modified:
incubator/trafficserver/site/trunk/docs/admin/http.htm
Modified: incubator/trafficserver/site/trunk/docs/admin/http.htm
URL: http://svn.apache.org/viewvc/incubator/trafficserver/site/trunk/docs/admin/http.htm?rev=898518&r1=898517&r2=898518&view=diff
==============================================================================
--- incubator/trafficserver/site/trunk/docs/admin/http.htm (original)
+++ incubator/trafficserver/site/trunk/docs/admin/http.htm Tue Jan 12 21:16:45 2010
@@ -10,193 +10,185 @@
<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"><em>Understanding HTTP Web Proxy Caching</em></a></li>
-<li><a href="#EnsuringCachedObjectFreshness"><em>Ensuring Cached Object Freshness</em></a></li>
-<li><a href="#SchedulingUpdatesToLocalCacheContent"><em>Scheduling Updates to Local Cache Content</em></a></li>
-<li><a href="#PushingContentIntoCache"><em>Pushing Content into the Cache</em></a></li>
-<li><a href="#PinningContentInCache"><em>Pinning Content in the Cache</em></a></li>
-<li><a href="#ToCacheOrNotToCache"><em>To Cache or Not to Cache?</em></a></li>
-<li><a href="#ForcingObjectCaching"><em>Forcing Object Caching</em></a></li>
-<li><a href="#CachingHTTPAlternates"><em>Caching HTTP Alternates</em></a></li>
-<li><a href="#UsingCongestionControl"><em>Using Congestion Control</em></a></li>
+<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 <em>web proxy server</em> so that it can serve these requests. After a web proxy server receives requests for web objects, it either serves the requests or forwards them to the <em>origin server</em> (the web server that contains the original copy of the requested information).
-The Traffic Server proxy supports <em>explicit proxy caching</em>, in which the userâs client software must be configured to send requests directly to the Traffic Server proxy.
+<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 (cache). </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 <i>cache hit</i> (see the figure below).</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 <i>revalidation</i>). 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 <i>cache miss</i>) or if the server indicates the cached copy is no longer valid, then Traffic Server obtains the object from the origin server, simultaneously streaming it to the user and its own local cache (see the figure below). Subsequent requests for the object are served faster because the object can retrieved directly from cache.</p>
+<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 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 or should not be cached. The following sections discuss these issues in greater detail. </p>
+<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 the 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>
+<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 <code>max-age</code> header</b><br />
+ <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> date</code> is the date in the objectâs server response header and <code>last_modified</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 that 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"><em>Modifying the Aging Factor for Freshness Computations</em></a>.<br />
- The computed freshness limit is bound by a minimum and maximum freshness limit; refer to <a href="#SettingAbsoluteFreshnessLimit"><em>Setting an Absolute Freshness Limit</em></a>.</li>
+ 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; refer to <a href="#SettingAbsoluteFreshnessLimit"><em>Setting an Absolute Freshness Limit</em></a>.</li>
+ 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#48049"><em>cache.config</em></a>.</li>
+ 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#48049">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 your needs. </p>
+<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><br />
-<table width="1232" border="1">
- <tr>
- <th width="322" scope="col">Variable</th>
- <th width="894" 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>
+ <li>Edit the following variable:</li>
+ <table width="1232" border="1">
+ <tr>
+ <th width="322" scope="col">Variable</th>
+ <th width="894" 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>
-<br />
<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 <i>absolute freshness limit</i>.</p>
+<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>
- <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.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 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.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>
-<br />
-<li>Save and close the <code>records.config</code> file.</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 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 (ie, very few objects have explicit expiration information).</p>
+<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>
-<br />
-<table width="1232" border="1">
- <tr>
- <th width="322" scope="col">Variable</th>
- <th width="894" scope="col">Description</th>
- </tr>
- <tr>
- <td><code><i>proxy.config.http.cache.required_headers</i></code></td>
- <td><p>Set this variable to one of the following values:<br />
- 0 = No headers required for an HTTP object to be stored in the cache.<br />
- 1 = At least last-modified header required for an HTTP object to be stored in the cache.<br />
+ <table width="1232" border="1">
+ <tr>
+ <th width="322" scope="col">Variable</th>
+ <th width="894" scope="col">Description</th>
+ </tr>
+ <tr>
+ <td><code><i>proxy.config.http.cache.required_headers</i></code></td>
+ <td><p>Set this variable to one of the following values:<br />
+ 0 = No headers required for an HTTP object to be stored in the cache.<br />
+ 1 = At least last-modified header required for an HTTP object to be stored in the cache.<br />
2 = Expires or max-age headers required for an HTTP object to be stored in the cache.</p> </td>
- </tr>
+ </tr>
</table>
-<br />
<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 might have 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 the cache: </p>
+<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 to serve no objects directly from the cache and therefore 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"><em>Configuring Traffic Server to Ignore Client no-cache Headers</em></a>. </li>
+ <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 <em>acceptable freshness tolerance</em>. 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>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 it's not served if its age is greater than its <code>max-age</code>.</p>
+ <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 <i>revalidation</i> 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>
+ <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"><em>HTTP Object Freshness</em></a>. You can reconfigure how Traffic Server evaluates freshness by selecting one of the following options: </p>
+<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>Always revalidate HTTP objects in the cache with the origin server; Traffic Server considers all HTTP objects in the cache to be stale.</li>
- <li>Never revalidate HTTP objects in the cache with the origin server; Traffic Server considers all HTTP objects in the cache to be fresh. </li>
- <li>Revalidate all HTTP objects without <code>Expires</code> or <code>Cache-Control</code> headers; Traffic Server considers all HTTP objects without <code>Expires</code> or <code>Cache-control</code> headers to be stale. </li>
+ <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 use Traffic Manager to edit the <code>records.config</code> file. In addition to the revalidation options listed above, you can also set specific revalidation rules in the <code>cache.config</code> file (refer to <a href="files.htm#48049"><em><code>cache.config</code></em></a>).</p>
+ <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#48049">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>
- <br />
-<table width="1232" border="1">
- <tr>
- <th width="322" scope="col">Variable</th>
- <th width="894" 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 />
+ <table width="1232" border="1">
+ <tr>
+ <th width="322" scope="col">Variable</th>
+ <th width="894" 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>
+ </tr>
</table>
-<br />
-<li>Save and close the<code> records.config </code>file. </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 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 <i>scheduled update</i> 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 that you can preload content you anticipate will be in demand. </p>
-<p>To use the <b>scheduled update</b> option, you must perform the following tasks. </p>
+ <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 and, for each URL, derives all recursive URLs (if applicable). It 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 <i>Force Immediate Update</i> 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"><em>Forcing an Immediate Update</em></a>. </p>
+ <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>
- <p>To configure the scheduled update option, follow the steps below:</p>
+ <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#235005"><em><code>update.config</code></em></a>). </li>
+ <li>Enter a line in the file for each URL you want to update (refer to <a href="files.htm#235005">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>
- <br />
<table width="1232" border="1">
<tr>
<th width="322" scope="col">Variable</th>
@@ -219,19 +211,17 @@
<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>
- <br />
- <li>Save and close the <code>records.config</code> file.</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 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 <i>Force Immediate Update</i> 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>
+<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>
- <br />
<table width="1232" border="1">
<tr>
<th width="322" scope="col">Variable</th>
@@ -242,20 +232,18 @@
<td><p>Set this variable to 1 to enable the Force Immediate Update option.</p> </td>
</tr>
</table>
- <br />
-
- <li>Make sure that the variable <code>proxy.config.update.enabled</code> is set to 1. </li>
+ <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>proxy.config.update.force</code> to <code>0</code> (zero).</p>
+<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 PUSH requests: </h5>
+<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 />
@@ -264,9 +252,8 @@
</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 config directory. </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>
- <br />
<table width="1232" border="1">
<tr>
<th width="322" scope="col">Variable</th>
@@ -277,12 +264,11 @@
<td><p>Set this variable to 1 to enable Traffic Server to accept PUSH requests.</p> </td>
</tr>
</table>
- <br />
- <li>Save and close the <code>records.config</code> file. </li>
+ <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>
+<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>
@@ -290,19 +276,18 @@
<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>
+ <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 <i>cache pinning option</i> configures Traffic Server to keep certain HTTP objects in the cache for a specified time. You can use this option to ensure 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 cacheable.</p>
-<h5>To set cache pinning rules and enable cache pinning: </h5>
+ <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#48049"><em><code>cache.config</code></em></a> for more information. </li>
+ 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#48049">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>
- <br />
<table width="1232" border="1">
<tr>
<th width="322" scope="col">Variable</th>
@@ -313,32 +298,30 @@
<td><p>Set this variable to 1 to enable the cache pinning option.</p> </td>
</tr>
</table>
- <br />
- <li>Navigate to the Traffic Server <code>bin</code> directory.<br />
+ <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>
+<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 not cache objects with the following request headers: </p>
+ <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 />
- You can configure Traffic Server to ignore the <code>Cache-Control: no-cache</code> header; refer to <a href="#NoCacheHeaders"><em>Configuring Traffic Server to Ignore Client no-cache Headers</em></a>. </li>
+ 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; refer to <a href="#CachingCookiedObjects"><em>Caching Cookied Objects</em></a>.</li>
+ 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 no-cache headers: </h5>
+<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>
- <br />
<table width="1232" border="1">
<tr>
<th width="322" scope="col">Variable</th>
@@ -349,31 +332,29 @@
<td><p>Set this variable to 1 to ignore client requests to bypass the cache.</p> </td>
</tr>
</table>
- <br />
- <li>Save and close the <code>records.config</code> file. </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 command <code>traffic_line -x</code> to apply the configuration changes. </li>
</ol>
<h3>Origin Server Directives </h3>
- <p>By default, Traffic Server does not cache objects with the following response headers: </p>
+ <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 />
- You can configure Traffic Server to ignore WWW-Authenticate headers; refer to <a href="#ConfiguringTrafficEdgeIgnoreWWWAuthenticateHeaders"><em>Configuring Traffic Server to Ignore WWW-Authenticate Headers</em></a>. </li>
+ 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 />
- You can configure Traffic Server to ignore <code>no-cache</code> headers; refer to <a href="#ConfiguringTrafficEdgeIgnoreServerNoCacheHeaders"><em>Configuring Traffic Server to Ignore Server no-cache Headers</em></a>. </li>
+ 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 no-cache headers: </h5>
+<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>
- <br />
<table width="1232" border="1">
<tr>
<th width="322" scope="col">Variable</th>
@@ -384,19 +365,18 @@
<td><p>Set this variable to 1 to ignore server directives to bypass the cache.</p> </td>
</tr>
</table>
- <br />
- <li>Save and close the <code>records.config</code> file. </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 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 that the client uses when preparing the authentication challenge response to an origin server. You can configure Traffic Server to ignore origin server <code>WWW-Authenticate</code> headers, in which case, objects with <code>WWW-Authenticate</code> headers are stored in the cache for future requests. 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 WWW-Authenticate headers: </h5>
+<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 records.config file located in the Traffic Server <code>config</code> directory. </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>
- <br />
<table width="1232" border="1">
<tr>
<th width="322" scope="col">Variable</th>
@@ -407,26 +387,25 @@
<td><p>Set this variable to 1 to cache objects with WWW Authenticate headers.</p> </td>
</tr>
</table>
- <br />
- <li>Save and close the <code>records.config</code> file. </li>
+ <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: </p>
+<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"><em>Disabling HTTP Object Caching</em></a>.</li>
- <li>Cache dynamic content (objects with URLs that contain a question mark (?), a semicolon (;), or cgi or that end in <code>.asp</code>); refer to <a href="#CachingDynamicContent"><em>Caching Dynamic Content</em></a>. </li>
- <li>Cache objects served in response to the <code>Cookie:</code> header; refer to <a href="#CachingCookiedObjects"><em>Caching Cookied Objects</em></a>. </li>
- <li>Observe never-cache rules in the <code>cache.config</code> file; refer to <a href="files.htm#48049"><em>cache.config</em></a>.</li>
+ <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#48049">cache.config</a>).</li>
</ul>
- <h4 id="DisablingHTTPObjectCaching"> Disabling HTTP Object Caching</h4>
+<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>
- <br />
<table width="1232" border="1">
<tr>
<th width="322" scope="col">Variable</th>
@@ -437,18 +416,16 @@
<td><p>Set this variable to 0 (zero) to disable HTTP object caching.</p> </td>
</tr>
</table>
- <br />
- <li>Save and close the <code>records.config</code> file. </li>
+ <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 <i>dynamic</i> if it ends in <code>.asp</code> or contains a question mark (?), a semicolon (;), or cgi. By default, Traffic Server does <em>not</em> cache dynamic content. You can configure Traffic Server to cache dynamic content, although it's recommend for specialized proxy situations only.</p>
+<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>
- <br />
<table width="1232" border="1">
<tr>
<th width="322" scope="col">Variable</th>
@@ -459,16 +436,15 @@
<td><p>Set this variable to 1 to cache dynamic content.</p> </td>
</tr>
</table>
- <br />
- <li>Save and close the <code>records.config</code> file. </li>
+ <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 as well as 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>
+<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><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>
@@ -476,8 +452,7 @@
<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">
+ <table width="1232" border="1">
<tr>
<th width="387" scope="col">Variable</th>
<th width="829" scope="col">Description</th>
@@ -491,30 +466,28 @@
3 = Cache all responses to cookies except text content-types (the default).</p> </td>
</tr>
</table>
- <br />
- <li>Save and close the <code>records.config</code> file. </li>
+ <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>
+<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#48049"><em><code>cache.config</code></em></a>. </li>
+ 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#48049">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 <i>alternates</i> 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>
-<p><b>To configure how Traffic Server caches alternates, follow the steps below:</b></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 variables:</li>
- <br />
+ <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="1232" border="1">
<tr>
<th width="394" scope="col">Variable</th>
@@ -536,21 +509,21 @@
<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 <code><i>proxy.config.http.cache.cache_responses_to_cookies</i></code> variable is set appropriately. For example, if you set the <code><i>proxy.config.http.cache.cache_responses_to_cookies</i> </code>variable 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>
+ </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>
+</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>
-<br />
<table width="1232" border="1">
<tr>
<th width="322" scope="col">Variable</th>
@@ -561,29 +534,27 @@
<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>
- <br />
- <li>Save and close the <code>records.config</code> file. </li>
+ <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 congestion control option enables you to configure Traffic Server to stop forwarding HTTP requests to origin servers when they become congested; it send the client a message to retry the congested origin server later. </p>
- <p>To use the congestion control option, you must perform the following tasks: </p>
+ <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>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>
+ <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>
+ <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>
-<br />
<table width="1232" border="1">
<tr>
<th width="322" scope="col">Variable</th>
@@ -594,10 +565,9 @@
<td><p>Set this variable to 1 to enable the congestion control option.</p> </td>
</tr>
</table>
- <br />
- <li>Save and close the <code>records.config</code> file. </li>
+ <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 that specify which origin servers are tracked for congestion and the timeout values Traffic Server uses to determine congestion; refer to <a href="files.htm#220539"><em>congestion.config</em></a> for the rule format. </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#220539">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>