Workers HowTo

+ + &project; + + 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. + + +Workers HowTo +Henri Gomez +Gal Shachor +Mladen Turk +$Date: 2010-01-28 20:47:58 +0100 (Thu, 28 Jan 2010) $ + + +

+A Tomcat worker is a Tomcat instance that is waiting to execute servlets on behalf of some web server. +For example, we can have a web server such as Apache forwarding servlet requests to a +Tomcat process (the worker) running behind it. +

+The scenario described above is a very simple one; +in fact one can configure multiple Tomcat workers to serve servlets on +behalf of a certain web server. +The reasons for such configuration can be: +

+We want different contexts to be served by different Tomcat workers to provide a +development environment where all the developers share the same web server but own a Tomcat worker of their own. +
+We want different virtual hosts served by different Tomcat processes to provide a +clear separation between sites belonging to different companies. +
+We want to provide load balancing, meaning run multiple Tomcat workers each on a +machine of its own and distribute the requests between them. +

+ +

+There are probably more reasons for having multiple workers but I guess that this list is enough... +Tomcat workers are defined in a properties file dubbed workers.properties and this tutorial +explains how to work with it. +

+ +

+This document was originally part of Tomcat: A Minimalistic User's Guide written by Gal Shachor, +but has been split off for organisational reasons. +

+ +

+Defining workers to the Tomcat web server plugin can be done using a properties file +(a sample file named workers.properties is available in the conf/ directory). +

+ +

+the file contains entries of the following form: +

+ +

+worker.list=<a comma separated list of worker names> +

+ + + # the list of workers + worker.list= worker1, worker2 + + +

+When starting up, the web server plugin will instantiate the workers whose name appears in the +worker.list property, these are also the workers to whom you can map requests. The directive can be used multiple times. +

+ + +

+Each named worker should also have a few entries to provide additional information on his behalf. +This information includes the worker's type and other related worker information. +Currently the following worker types that exists are (JK 1.2.5): +

+ + + + + + + + +

Type	Description
ajp12	This worker knows how to forward requests to out-of-process Tomcat workers using the ajpv12 protocol.
ajp13	This worker knows how to forward requests to out-of-process Tomcat workers using the ajpv13 protocol.
jni	DEPRECATED: This worker knows how to forward requests to in-process Tomcat workers using JNI.
lb	This is a load-balancing worker; it knows how to provide round-robin based sticky load balancing with a certain level of fault-tolerance.
status	This is a status worker for managing load balancers.

+ +

+Defining workers of a certain type should be done with the following property format: +

+ +

+worker.worker name.type=<worker type> +Where worker name is the name assigned to the worker and the worker type is one of the four types defined +in the table (a worker name may only contain any space the characters [a-zA-Z0-9\-_]). +

+ + + # Defines a worker named "local" that uses the ajpv12 protocol to forward requests to a Tomcat process. + worker.local.type=ajp12 + # Defines a worker named "remote" that uses the ajpv13 protocol to forward requests to a Tomcat process. + worker.remote.type=ajp13 + # Defines a worker named "loadbalancer" that loadbalances several Tomcat processes transparently. + worker.loadbalancer.type=lb + + + + +

+ +

+After defining the workers you can also specify properties for them. +Properties can be specified in the following manner: +

+ +

+worker.<worker name>.<property>=<property value> +

+ +Each worker has a set of properties that you can set as specified in the following subsections: + + +

+The ajp12 has been deprecated with Tomcat 3.3.x and you should use instead +ajp13 which is the only ajp protocol known by Tomcat 4.x and 5 and 5.5 and Tomcat 6. +

+The ajp12 typed workers forward requests to out-of-process Tomcat workers +using the ajpv12 protocol over TCP/IP sockets. +

+ +

+the ajp12 worker properties are : +

+ +

+host property sets the host where the Tomcat worker is listening for ajp12 requests. +

+ +

+port property sets the port where the Tomcat worker is listening for ajp12 requests +

+ +

+lbfactor property is used when working with a load balancer worker, this is the load-balancing factor for the worker. +We'll see more on this in the lb worker section. +

+ + + # worker "worker1" will talk to Tomcat listening on machine www.x.com at port 8007 using 2 lb factor + worker.worker1.host=www.x.com + worker.worker1.port=8007 + worker.worker1.lbfactor=2 + + +

+Notes: In the ajpv12 protocol, connections are created, used and then closed at each request. +The default port for ajp12 is 8007 +

+ + + + +

+The ajp13 typed workers forward requests to out-of-process Tomcat workers using the ajpv13 protocol over TCP/IP sockets. +The main difference between ajpv12 and ajpv13 are that: +

+ajpv13 is a more binary protocol and it tries to compress some of the request data by coding +frequently used strings as small integers. +
+ajpv13 reuses open sockets and leaves them open for future requests (remember when you've got a Firewall between your +web server and Tomcat). +
+ajpv13 has special treatment for SSL information so that the container can implement +SSL related methods such as isSecure(). +

+ +

+You should note that Ajp13 is now the only out-process protocol supported by Tomcat 4.0.x, 4.1.x, 5.0.x, 5.5.x and 6. +

+ + + + # worker "worker2" will talk to Tomcat listening on machine www2.x.com at port 8009 using 3 lb factor + worker.worker2.host=www2.x.com + worker.worker2.port=8009 + worker.worker2.lbfactor=3 + # worker "worker2" uses connections, which will stay no more than 10mn in the connection pool + worker.worker2.connection_pool_timeout=600 + # worker "worker2" ask operating system to send KEEP-ALIVE signal on the connection + worker.worker2.socket_keepalive=1 + # mount can be used as an alternative to the JkMount directive + worker.worker2.mount=/contexta /contexta/* /contextb /contextb/* + + +

+Notes: In the ajpv13 protocol, the default port is 8009 +

+ + + + +

+The load-balancing worker does not really communicate with Tomcat workers. +Instead it is responsible for the management of several "real" workers. +This management includes: +

+ +

+Instantiating the workers in the web server. +
+Using the worker's load-balancing factor, perform weighed-round-robin load balancing where +high lbfactor means stronger machine (that is going to handle more requests) +
+Keeping requests belonging to the same session executing on the same Tomcat worker. +
+Identifying failed Tomcat workers, suspending requests to them and instead falling-back on +other workers managed by the lb worker. +

+ +

+The overall result is that workers managed by the same lb worker are load-balanced (based on their lbfactor and current user session) and also fall-backed so a single Tomcat process death will not "kill" the entire site. +The following table specifies some properties that the lb worker can accept: +

balance_workers is a comma separated list of workers that the load balancer need to manage. +As long as these workers should only be used via the load balancer worker, +there is no need to also put them into the worker.list property. +This directive can be used multiple times for the same load balancer.
sticky_session specifies whether requests with SESSION ID's should be routed back to the same +Tomcat worker. Set sticky_session to False when Tomcat is using a Session Manager which +can persist session data across multiple instances of Tomcat. By default sticky_session is set to True.

+ + + # The worker balance1 while use "real" workers worker1 and worker2 + worker.balance1.balance_workers=worker1, worker2 + + + + + +

+The status worker does not communicate with Tomcat. +Instead it is responsible for the load balancer management. +

+ + # Add the status worker to the worker list + worker.list=jkstatus + # Define a 'jkstatus' worker using status + worker.jkstatus.type=status + +

Next thing is to mount the requests to the jkstatus worker. For Apache +web servers use the:

+ + # Add the jkstatus mount point + JkMount /jkmanager/* jkstatus + +

To obtain a higher level of security use the:

+ + # 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> + + + + + +

+You can define "macros" in the property files. +These macros let you define properties and later on use them while +constructing other properties. +

+ + + # property example, like a network base address + mynet=194.226.31 + # Using the above macro to simplify the address definitions + # for a farm of workers. + worker.node1.host=$(mynet).11 + worker.node2.host=$(mynet).12 + worker.node3.host=$(mynet).13 + + + + + +

+Workers can reference configurations of other workers. +If worker "x" references worker "y", then it inherits all +configuration parameters from "y", except for the ones +that have explicitly been set for "x". +

+ + + # worker toe defines some default settings + worker.toe.type=ajp13 + worker.toe.socket_keepalive=true + worker.toe.connect_timeout=10000 + worker.toe.recovery_options=7 + # workers tic and tac inherit those values + worker.tic.reference=worker.toe + worker.tac.reference=worker.toe + + +

+Please note, that the reference contains +the full prefix to the referenced configuration attributes, +not only the name of the referenced worker. +

+ +

+References can be nested. Be careful to avoid loops! +

+ +

+Attributes which are allowed multiple times for a single worker +can not be merged from a worker and a reference. An attribute +is only inherited from a reference, if it is not already set +for the referring worker. +

+ +

+References are especially useful, when configuring load balancers. +Try to understand the following two stage references: +

+ + + # We only use one load balancer + worker.list=lb + # Let's define some defaults + worker.basic.port=8009 + worker.basic.type=ajp13 + worker.basic.socket_keepalive=true + worker.basic.connect_timeout=10000 + worker.basic.recovery_options=7 + # And we use them in two groups + worker.lb1.domain=dom1 + worker.lb1.distance=0 + worker.lb1.reference=worker.basic + worker.lb2.domain=dom2 + worker.lb2.distance=1 + worker.lb2.reference=worker.basic + # Now we configure the load balancer + worker.lb.type=lb + worker.lb.method=B + worker.lb.balanced_workers=w11,w12,w21,w22 + worker.w11.host=myhost11 + worker.w11.reference=worker.lb1 + worker.w12.host=myhost12 + worker.w12.reference=worker.lb1 + worker.w21.host=myhost21 + worker.w21.reference=worker.lb2 + worker.w22.host=myhost22 + worker.w22.reference=worker.lb2 + + + + +

+ +

+Since coping with worker.properties on your own is not an easy thing to do, +a sample worker.properties file is bundled along JK. +

+ +

+You could also find here a sample workers.properties defining : +

+ +

+An ajp12 worker that used the host localhost and the port 8007 +
+An ajp13 worker that used the host localhost and the port 8008 +
+An lb worker that load balance the ajp12 and ajp13 workers +

+ + + # Define 3 workers, 2 real workers using ajp12, ajp13, the last one being a loadbalancing worker + worker.list=worker1, worker2, worker3 + # Set properties for worker1 (ajp12) + worker.worker1.type=ajp12 + worker.worker1.host=localhost + worker.worker1.port=8007 + worker.worker1.lbfactor=1 + # Set properties for worker2 (ajp13) + worker.worker2.type=ajp13 + worker.worker2.host=localhost + worker.worker2.port=8009 + worker.worker2.lbfactor=1 + worker.worker2.connection_pool_timeout=600 + worker.worker2.socket_keepalive=1 + worker.worker2.socket_timeout=60 + # Set properties for worker3 (lb) which use worker1 and worker2 + worker.worker3.balance_workers=worker1,worker2 + + +

+ +