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diff --git a/doc/glossary.html b/doc/glossary.html new file mode 100644 index 0000000..66ddc49 --- /dev/null +++ b/doc/glossary.html @@ -0,0 +1,603 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<html> +<head> + <title>mod_qos - Additional Information</title> +<meta http-equiv="content-type" content="text/html; charset=ISO-8859-1" /> +<meta name="author" content="Pascal Buchbinder" /> +<meta name="KeyWords" content="mod_qos, Quality of Service, Apache Web Server" /> +<link rel="shortcut icon" href="favicon.ico" /> +<style TYPE="text/css"> +<!-- + body { + background-color: white; + color: black; + font-family: sans-serif, arial, verdana; + font-weight: normal; + text-align: left; + } + a:link { color:#00673F; text-decoration:none; } + a:visited { color:#00673F; text-decoration:none; } + a:focus { color:black; text-decoration:underline; } + a:hover { color:black; text-decoration:underline; } + a:active { color:black; text-decoration:underline; } + syntax { font-family: monospace; font-size: 14; line-height: 1.6; } + .btable { font-size:0.75em; } +--> +</style> +</head> +<body> +<!-- + + Quality of service module for Apache Web Server. + + See http://mod-qos.sourceforge.net/ for further details. + + Copyright (C) 2023 Pascal Buchbinder + + Licensed to the Apache Software Foundation (ASF) under one or more + contributor license agreements. See the NOTICE file distributed with + this work for additional information regarding copyright ownership. + The ASF licenses this file to You under the Apache License, Version 2.0 + (the "License"); you may not use this file except in compliance with + the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. + +--> +<table> +<tbody> +<tr><td><a href="index.html"><img src="images/mod_qos.gif" alt="mod_qos" title="mod_qos" /></a></td> + <td style="vertical-align: bottom;"><h1>Additional Information</h1></td></tr> +<tr><td> </td> + <td> + + +<p> +This page gives you additional information on certain aspects of +<a href="index.html">mod_qos</a> to get a better understanding about +how to use the module. +</p> +<hr> + +<p> + <ul> + <li><a href="#directives">Directives</a></li> + <li><a href="#rules">Rules</a></li> + <li><a href="#variables">Environment Variables</a></li> + <li><a href="#concurrency">Concurrency Counter</a></li> + <ul> + <li><a href="#QS_LocRequestLimit_Example">Sample Use Case</a></li> + </ul> + <li><a href="#repeat">Repeat Counter</a></li> + <li><a href="#throughput">Throughput Control</a></li> + <ul> + <li><a href="#requestPerSecond">Requests per Second</a></li> + </ul> + <li><a href="#serialization">Serialization</a></li> + <li><a href="#ssi">Error Pages and Server Side Includes (SSI)</a></li> + <li><a href="#UserTracking">User Tracking</a></li> + <li><a href="#RequestStatistics">Request Statistics Using <i>qslog</i></a></li> + </ul> +</p> + + +<!-- --------------------------------------------------------- --> +<hr> +<a name="directives"></a> +<h2>Directives</h2> +<p> +The module is configured by directives. All directives process the +connection, HTTP request, and response data in a pre-defined sequence. +The following graph shows the order in which the directives work. +</p> +<p> +<a href="images/directive_seq.gif"><img src="images/directive_seq.gif" height="435" width="558" title="directive sequence" alt="directive sequence"/></a> +</p> + + +<!-- --------------------------------------------------------- --> +<hr> +<a name="rules"></a> +<h2>Rules</h2> +<p> +<a href="index.html">mod_qos</a> allows you to configure different kind of +rules. The main component of a rule is its counter. A rule measures either +the <a href="#concurrency">concurrency</a> (how many times something happens +at the same time), the <a href="#repeat">occurrence </a> (how often does +something happen in a certain amount of time), or the +<a href="#throughput">throughput</a> (sent amount of data or number of +request) and stores this information within that counter.</p> +<p> +Every rule has it's own threshold and maintains its own counter. A rule +is identified by either an URL pattern/matching string or by an +<a href="#variables">environment variable name</a>. +You can configure as many rules as you want. </p> +<img src="images/Rule.png" height="164" width="514" alt="Rule" /> +<p> +<i>Note: Some counters are only available once. This applies to the counters of +the rules using the +<code><a href="index.html#QS_Block">QS_Block</a></code>, +<code><a href="index.html#QS_SrvSerialize_var">QS_SrvSerialize</a></code>, and +<code><a href="index.html#QS_Serialize">QS_Serialize</a></code> +<a href="#variables">environment variables</a>. +</i> +</p> + + +<!-- --------------------------------------------------------- --> +<hr> +<a name="variables"></a> +<h2>Environment Variables</h2> +<p> +The Apache web server provides a mechanism for storing information +in so called <i>environment variables</i>. <a href="index.html">mod_qos</a> uses these +variables to exchange data respectively signalize events between +<a href="#rules">different rules</a> defined by the +<a href="#directives">corresponding directive</a>. These +variables can also be written or read by other Apache modules, such as +<a href="http://modsetenvifplus.sourceforge.net/">mod_setenvifplus <img src="images/link.png"/></a> +or <a href="http://httpd.apache.org/docs/current/mod/mod_setenvif.html">mod_setenvif <img src="images/link.png"/></a>. +</p> +<p>Example:<br> +The <code><a href="http://httpd.apache.org/docs/current/mod/mod_setenvif.html#setenvif">SetEnvIf <img src="images/link.png"/></a></code> directive +is used to set the <i>LimitLogin</i> variable if the request line matches +the <code>^/wp-login.php</code> pattern while the +<a href="index.html#QS_ClientEventLimitCount"><code>QS_ClientEventLimitCount</code></a> +directives increments the <a href="#repeat">repeat counter</a> having the same name +if the variable is present. +<br> +<img src="images/Events.png" height="396" width="795" alt="Event set by SetEnvIf and processed by QS_ClientEventLimitCount" /> +</p> +<p>It is also possible to write the values of these variables to your log +file using the format string <code>%{VARNAME}e</code> within the +<code><a href="http://httpd.apache.org/docs/current/mod/mod_log_config.html">TransferLog/CustomLog <img src="images/link.png"/></a></code> +directives. Or you can use them within error pages using +<a href="#ssi">server-side includes (SSI)</a>. +</p> +<p> +<i>Note: Whenever you use a directive (such as +<code><a href="http://modsetenvifplus.sourceforge.net/#SetEnvIfPlus">SetEnvIfPlus <img src="images/link.png"/></a></code>) which can either process request attributes (such +as HTTP headers) or environment variables, you must make sure that +a client can not bypass your rules by sending a request header +with the same name as the environment variable used in your configuration. +Use either the <a href="index.html#QS_RequestHeaderFilter">request header filter</a> +or the <code><a href="index.html#QS_UnsetReqHeader">QS_UnsetReqHeader</a></code> +directive to prevent anyone from sending a request header with the same name as +the variable you have defined. +</i></p> + +<!-- --------------------------------------------------------- --> +<hr> +<a name="concurrency"></a> +<h2>Concurrency Counter</h2> +<p> +A "concurrency counter" is used to determine how many times something +happens at the same time (concurrent), e.g. HTTP requests accessing the same +resource/URL at the same time. The rules using this counter type are either +defined by an <a href="#variables">environment variable name</a> or an +URL pattern (regular expression or a string matching the request's URL). +Such a rule automatically increments the counter when the Apache web server +starts to process a matching request and decrements the counter when the +request processing is completed. +</p> +<p> +You have to configure a threshold and the rule's variable name resp. URL +pattern. Requests (or new connections) are denied as soon as the configured +threshold is reached. +</p> +<p> +Directives using this counter type are: +<ul> +<li><a href="index.html#QS_LocRequestLimitMatch"><syntax>QS_LocRequestLimitMatch</syntax></a></li> +<li><a href="index.html#QS_LocRequestLimit"><syntax>QS_LocRequestLimit</syntax></a></li> +<li><a href="index.html#QS_CondLocRequestLimitMatch"><syntax>QS_CondLocRequestLimitMatch</syntax></a></li> +<li><a href="index.html#QS_EventRequestLimit"><syntax>QS_EventRequestLimit</syntax></a></li> +<li><a href="index.html#QS_ClientEventRequestLimit"><syntax>QS_ClientEventRequestLimit</syntax></a></li> +</ul> +Also the +<a href="index.html#QS_SrvMaxConn"><code>QS_SrvMaxConn</code></a>, +<a href="index.html#QS_SrvMaxConnClose"><code>QS_SrvMaxConnClose</code></a>, and +<a href="index.html#QS_SrvMaxConnPerIP"><code>QS_SrvMaxConnPerIP</code></a> +directives use this counter type, although with fewer parameter options. +</p> +<p> +<a name="QS_LocRequestLimit_Example"></a> +<h4>Sample Use Case</h4> +Now let us look at an example to show where these rules can be used. +Let's assume that you have two applications. We call them +"<font color="green">A</font>" and "<font color="blue">B</font>". +Application "<font color="green">A</font>" has been deployed on +path <code>/app/a</code> and "<font color="blue">B</font>" +on <code>/app/b</code>. +<table width="780px"> + <tr> +<td> </td> +<td> +As long as the server has enough resources, users can access both +applications the same time without influencing each other.<br> +All requests are processed quickly and the workers (w) become free +again to serve new requests. +<br><br> +</td> +<td> +<small> </small> <img src="images/qsloc1.png" height="216" width="408" alt="trouble-free"/> +</td> + </tr> + <tr> +<td> </td> +<td> +But if the application "<font color="blue">B</font>" becomes slow, +the duration of request processing increases and all workers (w) become busy. +There are no free workers left and application +"<font color="green">A</font>" becomes unavailable because of that. +<br><br> +</td> +<td> + <img src="images/qsloc2.png" height="212" width="422" alt="disruption"/> +</td> + </tr> + <tr> +<td> </td> +<td> +A <a href="index.html#QS_LocRequestLimit"><code>QS_LocRequestLimit</code></a> or +<a href="index.html#QS_LocRequestLimitMatch"><code>QS_LocRequestLimitMatch</code></a> +rule can help in such a situation. mod_qos limits the +number of requests to application "<font color="blue">B</font>" +so that application "<font color="green">A</font>" remains +available even if application "<font color="blue">B</font>" +has performance problems. +</td> +<td> + <img src="images/qsloc3.png" height="244" width="422" alt="disruption"/> +</td> + </tr> +</table> +<br> +Such a scenario can occur due to various infrastructure problems, +e.g., by slow database queries.<br> A similar situation can also +arise through an external influence: if someone penetrates application +"<font color="blue">B</font>" with a <i>HTTP GET / POST flood DoS attack</i>, +then application "<font color="green">A</font>" could also become +unreachable. +A <a href="index.html#QS_LocRequestLimit"><code>QS_LocRequestLimit</code></a> +rule can prevent this. +</p> + +<!-- --------------------------------------------------------- --> +<hr> +<a name="repeat"></a> +<h2>Repeat Counter</h2> +<p> +"Repeat counters" limit the number how often (Cr) something is allowed to +happen in a certain amount of time (Td). These rules trigger a timer whenever +the defined event occurs the first time and start to count every subsequent event +until the timer expires. If the event counter reaches the defined limitation, +requests are blocked until the time is up. +</p> +<p> + <img src="images/LimitCount.png" height="432" width="576" alt="reapet counter"/> +</p> +<p> +All repeat counters allow you to define an event which shall +increment the counter if they occur. You also have to configure a +duration Td and the threshold Cr, defining how many events are +allowed within the time Td.</p> +<p>Directive parameter example:<br> +<img src="images/LimitCountExample.png" height="165" width="574" alt="QS_ClientEventLimitCount" /> +</p> +<p> +While the counter is automatically cleared (set to 0) when the +time Td is up, you might also configure additional events to +<a href="index.html#_Decrement">decrement</a> or +<a href="index.html#_Clear">clear</a> the counter earlier. +</p> +<p> +The directives using this counter type are: +<ul> +<li><a href="index.html#QS_EventLimitCount"><syntax>QS_EventLimitCount</syntax></a></li> +<li><a href="index.html#QS_CondEventLimitCount"><syntax>QS_CondEventLimitCount</syntax></a></li> +<li><a href="index.html#QS_ClientEventLimitCount"><syntax>QS_ClientEventLimitCount</syntax></a></li> +<li><a href="index.html#QS_CondClientEventLimitCount"><syntax>QS_CondClientEventLimitCount</syntax></a></li> +<li><a href="index.html#QS_ClientEventBlockCount"><syntax>QS_ClientEventBlockCount</syntax></a></li> +</ul> +<i>Note: Some directives support the increase of the counter by more than "1" +taking the variable's value into account.</i> +</p> + + +<!-- --------------------------------------------------------- --> +<hr> +<a name="throughput"></a> +<h2>Throughput Control</h2> +<p> +Throughput control is implemented by measuring the current usage and +calculating a necessary delay which needs to be applied to the +data processing in order to achieve the desired limitation (closed +loop control system). +</p> +<p> + <img src="images/ClosedLoop.png" height="216" width="478" alt="closed loop"/> +</p> +<p> +<a href="index.html">mod_qos</a> can limit the bandwidth when downloading +data from your web server to the client. This throughput control can +be configured by the following directives: +<ul> +<li><a href="index.html#QS_LocKBytesPerSecLimitMatch"><syntax>QS_LocKBytesPerSecLimitMatch</syntax></a></li> +<li><a href="index.html#QS_LocKBytesPerSecLimit"><syntax>QS_LocKBytesPerSecLimit</syntax></a></li> +<li><a href="index.html#QS_EventKBytesPerSecLimit"><syntax>QS_EventKBytesPerSecLimit</syntax></a></li> +</ul> +<i>Note: Throughput control should always be used with a <a href="#concurrency">concurrency counter</a> +because the added delay increases the number of simultaneous requests. +</i></p> +<a name="requestPerSecond"></a> +<h3>Requests per Second</h3> +<p> +It is also possible to limit the number or requests per second to a +resource. This control function is less accurate than the bandwidth +limitation, since the measurement of the request rate takes longer +(several seconds) and the request delay is more coarse-grained.<br> +The following directive can be used to limit the number of requests +per second: +<ul> +<li><a href="index.html#QS_LocRequestPerSecLimitMatch"><syntax>QS_LocRequestPerSecLimitMatch</syntax></a></li> +<li><a href="index.html#QS_LocRequestPerSecLimit"><syntax>QS_LocRequestPerSecLimit</syntax></a></li> +<li><a href="index.html#QS_EventPerSecLimit"><syntax>QS_EventPerSecLimit</syntax></a></li> +<li><a href="index.html#QS_ClientEventPerSecLimit"><syntax>QS_ClientEventPerSecLimit</syntax></a></li> +</ul> +</p> + + +<!-- --------------------------------------------------------- --> +<hr> +<a name="serialization"></a> +<h2>Serialization</h2> +<p> +<a href="index.html">mod_qos</a> offers you the option to serialize requests. +Serialization means, that requests are processed one after the other. Incoming +requests are queued if another request is in process and have to wait until +the previous request is finished. +</p> +<p> + <img src="images/Serialization.png" height="336" width="570" alt="serialization"/> +</p> +<p> +Requests, which shall be serialized, are tagged by one of the following +<a href="#variables">environment variables</a>: +<ul> +<li><syntax><a href="index.html#QS_SrvSerialize_var">QS_SrvSerialize</a></syntax></li> +<li><syntax><a href="index.html#QS_Serialize">QS_Serialize</a></syntax></li> +</ul> +</p> +<p> +Serialization might be applied on a per +<a href="index.html#QS_SrvSerialize">server level</a> (serializing all HTTP +requests) or on a <a href="index.html#QS_ClientSerialize">per client level</a> +(serializing multiple requests coming from the same client/IP address). +</p> + + +<!-- --------------------------------------------------------- --> +<hr> +<a name="ssi"></a> +<a name="SSI"></a> +<h2>Error Pages and Server Side Includes (SSI)</h2> +<p> +Custom error documents to be used by <a href="index.html">mod_qos</a> +are either configured using the +<code><a href="index.html#QS_ErrorPage">QS_ErrorPage</a></code> directive +or the <code><a href="index.html#QS_ErrorPage_Var">QS_ErrorPage</a></code> +variable.<br> +You may also use Apache's <a href="http://httpd.apache.org/docs/current/howto/ssi.html">server-side includes (SSI) <img src="images/link.png"/></a> to generate the content +of the error document dynamically. The <a href="index.html#errorlog">error codes</a> and +other <a href="index.html#variables">variables</a> set by +<a href="index.html">mod_qos</a> can be used. +</p> +<p> +<table border="0" cellspacing="5" cellpadding="10" width="100%"> +<tr><td bgcolor="#E2EDE2"> +Sample configuration:<br> +<pre> +AddType text/html .shtml +AddOutputFilter INCLUDES .shtml +QS_ErrorPage <a href="#qs_error.shtml">/errorpages/qs_error.shtml</a> +</pre> +</td></tr> +</table> +</p> + +<p> +<table border="0" cellspacing="5" cellpadding="10" width="100%"> +<tr><td bgcolor="#E2EDE2"><a name="qs_error.shtml"></a> +Sample page:<br> +<pre> +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<html> + <head> + <!-- + -- mod_qos sample SSI error page (Apache 2.4) + --> + <meta http-equiv="Cache-Control" content="no-cache, no-store"/> + <meta http-equiv="expires" content="0" /> + <title>ERROR - <!--#echo var="REDIRECT_ERROR_NOTES" --></title> + </head> + <body> + <p> + <b><i>sorry - the server was unable to complete your request</i></b> + </p> + <p> + code: mod_qos(<!--#echo var="<a href="index.html#QS_ErrorNotes">QS_ErrorNotes</a>" -->)<br> + <!--#if expr="v('REDIRECT_ERROR_NOTES') =~ /00[0-9]/" --> + reason: initialisation failure + <!--#elif expr="v('REDIRECT_ERROR_NOTES') =~ /0[18][0-9]/" --> + reason: request rule + <!--#elif expr="v('REDIRECT_ERROR_NOTES') =~ /03[0-9]/" --> + reason: connection rule + <!--#elif expr="v('REDIRECT_ERROR_NOTES') =~ /[01]4[0-9]/" --> + reason: request filter + <!--#elif expr="v('REDIRECT_ERROR_NOTES') =~ /05[0-9]/" --> + reason: bandwidth limitation + <!--#elif expr="v('REDIRECT_ERROR_NOTES') =~ /[01]6[0-9]/" --> + reason: client limitation <br> + remaining time: <span id="remaining"><!--#echo var="<a href="index.html#QS_Limit_Remaining">QS_Limit_Remaining</a>" --></span> seconds + <script type="text/javascript"> + <!-- + setInterval(function () { + var msg = document.getElementById('remaining'); + if(msg) { + var value = msg.innerHTML; + var remainTime = value - 1; + if(remainTime < 0) { + window.location = window.location.pathname; + } else { + msg.innerHTML = remainTime; + } + } + }, 1000); + //--> + </script> + <!--#elif expr="v('REDIRECT_ERROR_NOTES') =~ /10[0-9]/" --> + reason: GEO location limitation + <!--#else --> + reason: generic failure + <!--#endif --> + </p> + </body> +</html> +</pre> +</td></tr> +</table> +</p> + + +<!-- --------------------------------------------------------- --> +<hr> +<a name="UserTracking"></a> +<a name="QS_UserTrackingCookieName"></a> +<h2>User Tracking</h2> +<p> +It might be necessary to identify individual users to define appropriate QoS +rules. For this reason, <a href="index.html">mod_qos</a> can set a cookie +containing a unique identifier. This identifier is then written to the +<code><a href="index.html#mod_qos_user_id">mod_qos_user_id</a></code> +environment variable and you can add it to your log files by the +format string <code>%{mod_qos_user_id}e</code>. This allows you to identify +all requests issued by a user.</p> +<p> +This feature is enabled by the following directive: +<ul> +<li><syntax>QS_UserTrackingCookieName <name> [<path>] [<domain>] ['session'] ['jsredirect']</syntax><br> +The parameter "name" defines the cookie's name and "domain" (optional) +the domain attribute for the Set-Cookie header. The string "session" can +be defined if the cookie should not be stored by the session (but can +be deleted when the user closes this browser). +</li> +</ul> +You can also enforce the browser to support cookies by specifying the +"path" parameter for the <code>QS_UserTrackingCookieName</code> directive. +This parameter defines an error document and mod_qos +answers the request with a redirect (302) to this document when setting +the cookie initially. The browser will follow the redirect and mod_qos +redirects the browser back to the initially requested page if the request +to this error document contains the tracking cookie. If the browser did not +send the cookie, the error document is shown. +</p> +<p> <img src="images/UserTracking.png" height="386" width="410" alt="user tracking cookie enforcement"/></p> +<p> +<i>Note: You can exclude certain clients from this enforcement by +setting the <code>DISABLE_UTC_ENFORCEMENT</code> +<a href="#variables">environment variable</a> +at server level (outside Location), e.g., to allow crawlers not +supporting cookies to access your site.</i> +</p> +<p> +<table border="0" cellspacing="5" cellpadding="10" width="100%"> +<tr><td bgcolor="#E2EDE2"> +Sample configuration:<br> +<pre> +<a href="index.html#QS_UserTrackingCookieName">QS_UserTrackingCookieName</a> qstrack <a href="#cookiecheck">/errorpages/cookiecheck.html</a> session +<a href="index.html#QS_SessionKey">QS_SessionKey</a> sB.F4_0%D700ahXT2 +</pre> +</td></tr> +</table> +</p> +<p> +<table border="0" cellspacing="5" cellpadding="10" width="100%"> +<tr><td bgcolor="#E2EDE2"><a name="cookiecheck"></a> +Sample page:<br> +<pre> +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> +<html> + <head> + <meta http-equiv="Cache-Control" content="no-cache, no-store"/> + <meta http-equiv="expires" content="0" /> + <title>Cookie Check Page</title> + </head> + <body> + <h1>Cookie Check Failed</h1> + <p> + Please enable cookies in your browser.<br> + Bitte schalten Sie in Ihrem Browser Cookies ein.<br> + Activez les cookies dans votre navigateur, s'il vous pla&icirc;t.<br> + Por favor active las cookies en su navegador.<br> + Si prega di attivare i cookies nel proprio browser.<br> + </p> + </body> +</html> +</pre> +</td></tr> +</table> +</p> + +<!-- --------------------------------------------------------- --> +<hr> +<a name="qslog"></a> +<a name="RequestStatistics"></a> +<h2>Request Statistics Using <i>qslog</i></h2> +<p> +<code><a href="qslog.1.html">qslog</a></code> is a command line tool to +generate usage statistics data from log files. It can generate the data in +real time if defined within your Apache's server configuration. +<table border="0" cellspacing="5" cellpadding="10" width="100%"> +<tr><td bgcolor="#E2EDE2"> +Sample configuration:<br> +<pre> +CustomLog "|/usr/bin/qslog -o logs/qslog.csv -x -f ISBDk" "%h %>s %b %D %k" +</pre> +</td></tr> +</table> +</p><p> +Or you can use it to process any existing log file using the post processing +option <code>-p</code>. This does not only work for +<a href="http://httpd.apache.org/docs/current/mod/mod_log_config.html">Apache log <img src="images/link.png"/></a> files but for any other log file as well. You just have to know what's in the log +and configure the format string argument <code>-f</code> of the +<code><a href="qslog.1.html">qslog</a></code> command accordingly. +</p> +<p> +Example:<br> +<img src="images/qslogFormat.png" height="381" width="738" alt="log format definition"/> +</p> +<p> +The output shows the data as a function of time: a summary of what happened every minute. +Each line includes all measured values as semicolon spearated name/value pairs (CSV). +</p> +<p> +You can use the spreadsheet program of your choice to process the output:<br><br> +<img src="images/qslog_spreadsheet_example.png" height="413" width="850" alt="spreadsheet"/> +</p> + +<!-- --------------------------------------------------------- --> +</td></tr> +</tbody> +</table> +<br> +<hr> +<SMALL><SMALL>© 2023, Pascal Buchbinder</SMALL></SMALL> +</body> +</html> |