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diff --git a/rubbos/app/tomcat-connectors-1.2.32-src/xdocs/generic_howto/loadbalancers.xml b/rubbos/app/tomcat-connectors-1.2.32-src/xdocs/generic_howto/loadbalancers.xml deleted file mode 100644 index eda22cd4..00000000 --- a/rubbos/app/tomcat-connectors-1.2.32-src/xdocs/generic_howto/loadbalancers.xml +++ /dev/null @@ -1,236 +0,0 @@ -<?xml version="1.0" encoding="ISO-8859-1"?> -<!DOCTYPE document [ - <!ENTITY project SYSTEM "project.xml"> -]> -<document url="loadbalancers.html"> - - &project; -<copyright> - 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. -</copyright> -<properties> -<title>LoadBalancer HowTo</title> -<author email="mturk@apache.org">Mladen Turk</author> -<date>$Date: 2011-03-07 19:04:44 +0100 (Mon, 07 Mar 2011) $</date> -</properties> -<body> -<section name="Introduction"> -<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> - -<subsection name="Basic Load Balancer Properties"> -<p>A worker is configured as a load balancer by setting its worker <code>type</code> -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 <code>worker.list</code> 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 <code>lbfactor</code> 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> - -<source> - # 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 -</source> - -<warn> -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 <code>jvmRoute</code> 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 <code>jvmRoute="worker1"</code>, Tomcat on host "myhost2" -needs <code>jvmRoute="worker2"</code>. -</warn> - -<p>For a complete reference of all load balancer configuration -attributes, please consult the worker <a href="../reference/workers.html">reference</a>. -</p> -</subsection> - -<subsection name="Advanced Load Balancer Worker Properties"> -<p>The load balancer supports complex topologies and failover configurations. -Using the member attribute <code>distance</code> 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 <code>domain</code> 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 <code>activation</code>. -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 -<code>activation</code> set to <b>disabled</b> in combination with -the attribute <code>redirect</code> added to the other workers:</p> - -<source> - # 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 -</source> - -<p> -The <code>redirect</code> 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 <code>activation</code> to <b>disabled</b>: -The session id coming with a request is send either -as part of the request URL (<code>;jsessionid=...</code>) 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 <code>JK_LB_ACTIVATION</code>. -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 -<code>JK_LB_ACTIVATION</code> has been added in version 1.2.32.</p> -</subsection> - -<subsection name="Status Worker properties"> -<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> -<source> - # Add the status worker to the worker list - worker.list=jkstatus - # Define a 'jkstatus' worker using status - worker.jkstatus.type=status -</source> -<p>Next thing is to mount the requests to the jkstatus worker. For Apache -web servers use the:</p> -<source> - # Add the jkstatus mount point - JkMount /jkmanager/* jkstatus -</source> -<p>To obtain a higher level of security use the:</p> -<source> - # 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> -</source> - -</subsection> - -</section> - -</body> -</document> |