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diff --git a/rubbos/app/tomcat-connectors-1.2.32-src/docs/generic_howto/printer/loadbalancers.html b/rubbos/app/tomcat-connectors-1.2.32-src/docs/generic_howto/printer/loadbalancers.html new file mode 100644 index 00000000..22999c94 --- /dev/null +++ b/rubbos/app/tomcat-connectors-1.2.32-src/docs/generic_howto/printer/loadbalancers.html @@ -0,0 +1,206 @@ +<html><head><META http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><title>The Apache Tomcat Connector - Generic HowTo - LoadBalancer HowTo</title><meta name="author" value="Mladen Turk"><meta name="email" value="mturk@apache.org"><link href="../../style.css" type="text/css" rel="stylesheet"></head><body bgcolor="#ffffff" text="#000000" link="#525D76" alink="#525D76" vlink="#525D76"><table border="0" width="100%" cellspacing="4"><!--PAGE HEADER--><tr><td colspan="2"><!--TOMCAT LOGO--><a href="http://tomcat.apache.org/"><img src="../../images/tomcat.gif" align="left" alt="Apache Tomcat" border="0"></a><!--APACHE LOGO--><a href="http://www.apache.org/"><img src="http://www.apache.org/images/asf-logo.gif" align="right" alt="Apache Logo" border="0"></a></td></tr><!--HEADER SEPARATOR--><tr><td colspan="2"><hr noshade size="1"></td></tr><tr><!--RIGHT SIDE MAIN BODY--><td width="80%" valign="top" align="left"><table border="0" width="100%" cellspacing="4"><tr><td align="left" valign="top"><h1>The Apache Tomcat Connector - Generic HowTo</h1><h2>LoadBalancer HowTo</h2></td><td align="right" valign="top" nowrap="true"><img src="../../images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"></td></tr></table><table border="0" cellspacing="0" cellpadding="2" width="100%"><tr><td bgcolor="#525D76"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Introduction"><strong>Introduction</strong></a></font></td></tr><tr><td><blockquote> +<br> +<p>A load balancer is a worker that does not directly communicate with Tomcat. +Instead it is responsible for the management of several "real" workers, +called members or sub workers of the load balancer.</p> +<p> +This management includes: +</p> +<ul> +<li> +Instantiating the workers in the web server. +</li> +<li> +Using the worker's load-balancing factor, perform weighted load balancing +(distributing load according to defined strengths of the targets). +</li> +<li> +Keeping requests belonging to the same session executing on the same Tomcat +(session stickyness). +</li> +<li> +Identifying failed Tomcat workers, suspending requests to them and instead +falling-back on other workers managed by the load balancer. +</li> +<li> +Providing status and load metrics for the load balancer itself and all +members via the status worker interface. +</li> +<li> +Allowing to dynamically reconfigure load-balancing via the status worker +interface. +</li> +</ul> +<p> +Workers managed by the same load balancer worker are load-balanced +(based on their configured balancing factors and current request or session load) +and also secured against failure by providing failover to other members of the same +load balancer. So a single Tomcat process death will not "kill" the entire site. +</p> +<p>Some of the features provided by a load balancer are even interesting, when +only working with a single member worker (where load balancing is not possible).</p> + +<table border="0" cellspacing="0" cellpadding="2" width="100%"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Basic Load Balancer Properties"><strong>Basic Load Balancer Properties</strong></a></font></td></tr><tr><td><blockquote> +<p>A worker is configured as a load balancer by setting its worker <b class="code">type</b> +to <b>lb</b>. +</p> +<p> +The following table specifies some properties used to configure a load balancer worker: +</p> +<ul> +<li><b>balance_workers</b> is a comma separated list of names of the member workers of the +load balancer. These workers are typically of type <b>ajp13</b>. The member workers do +not need to appear in the <b class="code">worker.list</b> property themselves, adding the +load balancer to it suffices.</li> +<li><b>sticky_session</b> specifies whether requests with SESSION ID's should be routed +back to the same Tomcat instance that created the session. You can set sticky_session to +<b>False</b> when Tomcat is using a session manager which can share session data across +multiple instances of Tomcat - or if your application is stateless. +By default sticky_session is set to <b>True</b>.</li> +<li><b>lbfactor</b> can be added to each member worker to configure individual +strengths for the members. A higher <b class="code">lbfactor</b> will lead to more +requests being balanced to that worker. The factors must be given by integers and the +load will be distributed proportional to the factors given. Higher factors lead to +more requests.</li> +</ul> + +<div class="example"><pre> + # The load balancer worker balance1 will distribute + # load to the members worker1 and worker2 + worker.balance1.type=lb + worker.balance1.balance_workers=worker1, worker2 + worker.worker1.type=ajp13 + worker.worker1.host=myhost1 + worker.worker1.port=8009 + worker.worker2.type=ajp13 + worker.worker1.host=myhost2 + worker.worker1.port=8009 +</pre></div> + +<p><font color="#ff0000"> +Session stickyness is not implemented using a tracking table for sessions. +Instead each Tomcat instance gets an individual name and adds its name at +the end of the session id. When the load balancer sees a session id, it +finds the name of the Tomcat instance and sends the request via the correct +member worker. For this to work you must set the name of the Tomcat instances +as the value of the <b class="code">jvmRoute</b> attribute in the Engine element of +each Tomcat's server.xml. The name of the Tomcat needs to be equal to the name +of the corresponding load balancer member. In the above example, Tomcat on host +"myhost1" needs <b class="code">jvmRoute="worker1"</b>, Tomcat on host "myhost2" +needs <b class="code">jvmRoute="worker2"</b>. +</font></p> + +<p>For a complete reference of all load balancer configuration +attributes, please consult the worker <a href="../../reference/workers.html">reference</a>. +</p> +</blockquote></td></tr></table> + +<table border="0" cellspacing="0" cellpadding="2" width="100%"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Advanced Load Balancer Worker Properties"><strong>Advanced Load Balancer Worker Properties</strong></a></font></td></tr><tr><td><blockquote> +<p>The load balancer supports complex topologies and failover configurations. +Using the member attribute <b class="code">distance</b> you can group members. +The load balancer will always send a request to a member of lowest distance. +Only when all of those are broken, it will balance to the members of the +next higher configured distance. This allows to define priorities between +Tomcat instances in different data center locations. +</p> +<p>When working with shared sessions, either by using session replication +or a persisting session manager (e.g. via a database), one often splits +up the Tomcat farm into replication groups. In case of failure of a member, +the load balancer needs to know, which other members share the session. +This is configured using the <b class="code">domain</b> attribute. All workers +with the same domain are assumed to share the sessions.</p> +<p>For maintenance purposes you can tell the load balancer to not +allow any new sessions on some members, or even not use them at all. +This is controlled by the member attribute <b class="code">activation</b>. +The value <b>Active</b> allows normal use of a member, <b>disabled</b> +will not create new sessions on it, but still allow sticky requests, +and <b>stopped</b> will no longer send any requests to the member. +Switching the activation from "active" to "disabled" some time before +maintenance will drain the sessions on the worker and minimize disruption. +Depending on the usage pattern of the application, draining will take from +minutes to hours. Switching the worker to stopped immediately before +maintenance will reduce logging of false errors by mod_jk.</p> +<p>Finally you can also configure hot spare workers by using +<b class="code">activation</b> set to <b>disabled</b> in combination with +the attribute <b class="code">redirect</b> added to the other workers:</p> + +<div class="example"><pre> + # The advanced router LB worker + worker.list=router + worker.router.type=lb + worker.router.balance_workers=worker1,worker2 + + # Define the first member worker + worker.worker1.type=ajp13 + worker.worker1.host=myhost1 + worker.worker1.port=8009 + # Define preferred failover node for worker1 + worker.worker1.redirect=worker2 + + # Define the second member worker + worker.worker2.type=ajp13 + worker.worker2.host=myhost2 + worker.worker2.port=8009 + # Disable worker2 for all requests except failover + worker.worker2.activation=disabled +</pre></div> + +<p> +The <b class="code">redirect</b> flag on worker1 tells the load balancer +to redirect the requests to worker2 in case that worker1 has a problem. +In all other cases worker2 will not receive any requests, thus acting +like a hot standby. +</p> + +<p>A final note about setting <b class="code">activation</b> to <b>disabled</b>: +The session id coming with a request is send either +as part of the request URL (<b class="code">;jsessionid=...</b>) or via a cookie. +When using bookmarks or browsers that are running since a long time, +it is possible to send a request carrying an old and invalid session id +pointing at a disabled member. +Since the load balancer does not have a list of valid sessions, it will +forward the request to the disabled member. Thus draining takes longer than +expected. To handle such cases, you can add a Servlet filter to your web +application, which checks the request attribute <b class="code">JK_LB_ACTIVATION</b>. +This attribute contains one of the strings "ACT", "DIS" or "STP". If you +detect "DIS" and the session for the request is no longer active, delete the +session cookie and redirect using a self-referential URL. The redirected +request will then no longer carry session information and thus the load +balancer will not send it to the disabled worker. The request attribute +<b class="code">JK_LB_ACTIVATION</b> has been added in version 1.2.32.</p> +</blockquote></td></tr></table> + +<table border="0" cellspacing="0" cellpadding="2" width="100%"><tr><td bgcolor="#828DA6"><font color="#ffffff" face="arial,helvetica.sanserif"><a name="Status Worker properties"><strong>Status Worker properties</strong></a></font></td></tr><tr><td><blockquote> +<p> +The status worker does not communicate with Tomcat. +Instead it is responsible for the worker management. It is +especially useful when combined with load balancer workers. +</p> +<div class="example"><pre> + # Add the status worker to the worker list + worker.list=jkstatus + # Define a 'jkstatus' worker using status + worker.jkstatus.type=status +</pre></div> +<p>Next thing is to mount the requests to the jkstatus worker. For Apache +web servers use the:</p> +<div class="example"><pre> + # Add the jkstatus mount point + JkMount /jkmanager/* jkstatus +</pre></div> +<p>To obtain a higher level of security use the:</p> +<div class="example"><pre> + # Enable the JK manager access from localhost only + <Location /jkmanager/> + JkMount jkstatus + Order deny,allow + Deny from all + Allow from 127.0.0.1 + </Location> +</pre></div> + +</blockquote></td></tr></table> + +</blockquote></td></tr></table></td></tr><!--FOOTER SEPARATOR--><tr><td colspan="2"><hr noshade size="1"></td></tr><!--PAGE FOOTER--><tr><td colspan="2"><div align="center"><font color="#525D76" size="-1"><em> + Copyright © 1999-2011, Apache Software Foundation + </em></font></div></td></tr></table></body></html>
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