hgomez 2002/09/09 02:16:42
Added: jk/xdocs/jk workershowto.xml
Log:
Add WorkersHowTo (still need works and review).
I'd like to see commiters check cache_timeout and socket_timeout.
Also I'll need informations of load balancing settings for error mode only
(failover)
Revision Changes Path
1.1 jakarta-tomcat-connectors/jk/xdocs/jk/workershowto.xml
Index: workershowto.xml
===================================================================
<?xml version="1.0" encoding="ISO-8859-1" ?>
<document>
<properties>
<title>Workers HowTo</title>
<author email="[EMAIL PROTECTED]">Henri Gomez</author>
<author email="[EMAIL PROTECTED]">Gal Shachor</author>
</properties>
<section name="Introduction">
<p>
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.
</p>
<p>
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:
</p>
<ul>
<li>
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.
</li>
<li>
We want different virtual hosts served by different Tomcat processes to provide a
clear separation between sites belonging to different companies.
</li>
<li>
We want to provide load balancing, meaning run multiple Tomcat workers each on a
machine of its own and distribute the requests between them.
</li>
</ul>
<p>
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.
</p>
<p>
This document was originally part of <b>Tomcat: A Minimalistic User's Guide</b>
written by Gal Shachor,
but has been split off for organizational reasons.
</p>
</section>
<section name="Defining Workers">
<p>
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).
</p>
<p>
the file contains entries of the following form:
</p>
<p>
<b>worker.list</b>=<a comma separated list of worker names>
</p>
<screen>
<note>the list of workers</note>
<read>worker.list= worker1, worker2</read>
</screen>
<p>
When starting up, the web server plugin will instantiate the workers whose name
appears in the
<b>worker.list</b> property, these are also the workers to whom you can map requests.
</p>
<subsection name="Workers Type">
<p>
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 1.2.0):
</p>
<table>
<tr><th>Type</th><th>Description</th></tr>
<tr><td>ajp12</td><td>This worker knows how to forward requests to out-of-process
Tomcat workers using the ajpv12 protocol.</td></tr>
<tr><td>ajp13</td><td>This worker knows how to forward requests to out-of-process
Tomcat workers using the ajpv13 protocol.</td></tr>
<tr><td>jni</td><td>This worker knows how to forward requests to in-process Tomcat
workers using JNI.</td></tr>
<tr><td>lb</td><td>This is a load-balancing worker; it knows how to provide
round-robin based sticky load balancing with a certain level of
fault-tolerance.</td></tr>
</table>
<p>
Defining workers of a certain type should be done with the following property format:
</p>
<p>
<b>worker</b>. <b>worker name</b>.<b>type</b>=<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 not contain any space (a good naming convention for
queue named should
follow the Java variable naming rules).
</p>
<screen>
<note>Defines a worker named "local" that uses the ajpv12 protocol to forward
requests to a Tomcat process.</note>
<read>worker.local.type=ajp12</read>
<note>Defines a worker named "remote" that uses the ajpv13 protocol to forward
requests to a Tomcat process.</note>
<read>worker.remote.type=ajp13</read>
<note>Defines a worker named "fast" that uses JNI to forward requests to a Tomcat
process.</note>
<read>worker.fast.type=jni</read>
<note>Defines a worker named "loadbalancer" that loadbalances several Tomcat
processes transparently.</note>
<read>worker.loadbalancer.type=lb</read>
</screen>
</subsection>
</section>
<section name="Setting Worker Properties">
<p>
After defining the workers you can also specify properties for them.
Properties can be specified in the following manner:
</p>
<p>
worker.<worker name>.<property>=<property value>
</p>
Each worker has a set of properties that you can set as specified in the following
subsections:
<subsection name="ajp12 Worker properties">
<p>
The ajp12 typed workers forward requests to out-of-process Tomcat workers
using the ajpv12 protocol over TCP/IP sockets.
</p>
<p>
the ajp12 worker properties are :
</p>
<p>
<b>host</b> property set the host where the Tomcat worker is listening for ajp12
requests.
</p>
<p>
<b>port</b> property set The port where the Tomcat worker is listening for ajp12
requests
</p>
<p>
<b>lbfactor</b>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.
</p>
<screen>
<note>worker "worker1" will talk to Tomcat listening on machine www.x.com at port
8007 using 2.5 lb factor</note>
<read>worker.worker1.host=www.x.com</read>
<read>worker.worker1.port=8007</read>
<read>worker.worker1.lbfactor=2.5</read>
</screen>
<p>
Notes: In the ajpv12 protocol, connections are created, used and then closed at each
request.
The default port for ajp12 is 8007
</p>
</subsection>
<subsection name="ajp13 Worker properties">
<p>
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:
<ul>
<li>
ajpv13 is a more binary protocol and it try to compress some of the request data by
coding
frequently used strings as small integers.
</li>
<li>
ajpv13 reuse open sockets and leaves them open for future requests (remember when
you've got a Firewall between your
WebServer and Tomcat).
</li>
<li>
ajpv13 has special treatment for SSL information so that the container can implement
SSL related methods such as isSecure().
</li>
</ul>
</p>
<p>
You should note that Ajp13 is now the only out-process protocol supported by Tomcat
4.0.x, 4.1.x and 5.
</p>
<p>
The following table specifies properties that the ajp13 worker can accept:
</p>
<p>
<b>host</b> property set the host where the Tomcat worker is listening for ajp13
requests.
</p>
<p>
<b>port</b> property set The port where the Tomcat worker is listening for ajp13
requests
</p>
<p>
<b>lbfactor</b> 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.
</p>
<p>
<b>cachesize</b> property is usefull when you're using jk in multithreaded
web servers such as Apache 2.0, IIS and Netscape. They will benefit the most by
setting this value to a higher level (such as the estimated average concurrent users
for Tomcat).
</p>
<p>
<b>cache_timeout</b> property should be used with <b>cachesize</b> to specify how to
time jk should keep
an open socket in cache before closing it. This property should be used to reduce
the number of threads
on the Tomcat WebServer.
</p>
<p>
You should know that under heavy load some WebServers, for example Apache's create
many childs/threads
to handle the load and they destroy the childs/threads only when the load decrease.
</p>
<p>
Each child could open an ajp13 connection if it have to forward a request to Tomcat,
creating
a new ajp13 thread on Tomcat side.
</p>
<p>
The problem is that after an ajp13 connection is created, the child won't drop it
until killed. And since the webserver will keep its childs/threads running
to handle high-load, even it the child/thread handle only static contents, you could
finish having many unused ajp13 threads on the Tomcat side.
</p>
<p>
<b>socket_keepalive</b> property should be used when you have a firewall between
your webserver
and the Tomcat engine, who tend to drop inactive connections. This flag will told
Operating System
to send <code>KEEP_ALIVE</code> message on inactive connections (interval depend on
global OS settings,
generally 120mn), and sus prevent the firewall to cut the connection.
</p>
<p>
The problem with Firewall cutting inactive connections is that sometimes, neither
webserver or tomcat
have informations about the cut and couldn't handle it.
</p>
<p>
<b>socket_timeout</b> property told webserver to cut an ajp13 connection after some
time of use.
It's a good way to ensure that there won't be any unused threads living on Tomcat
side, with the
extra cost of reopening sockets next time a request be forwarded.
This property is very similar to <b>cache_timeout</b> but works also in non-cache
mode.
</p>
<screen>
<note>worker "worker2" will talk to Tomcat listening on machine www2.x.com at port
8009 using 3.5 lb factor</note>
<read>worker.worker2.host=www2.x.com</read>
<read>worker.worker2.port=8009</read>
<read>worker.worker2.lbfactor=3.5</read>
<note>worker "worker2" use up to 10 sockets, which will stay no more than 10mn in
cache</note>
<read>worker.worker2.cachesize=10</read>
<read>worker.worker2.cache_timeout=600</read>
<note>worker "worker2" ask operating system to send KEEP-ALIVE signal on the
connection</note>
<read>worker.worker2.socket_keepalive=1</read>
<note>worker "worker2" want ajp13 connection to be dropped after 5mn (timeout)</note>
<read>worker.worker2.socket_timeout=300</read>
</screen>
<p>
Notes: In the ajpv13 protocol, the default port is 8009
</p>
</subsection>
<subsection name="lb Worker properties">
<p>
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:
</p>
<ul>
<li>
Instantiating the workers in the web server.
</li>
<li>
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)
</li>
<li>
Keeping requests belonging to the same session executing on the same Tomcat worker.
</li>
<li>
Identifying failed Tomcat workers, suspending requests to them and instead
fall-backing on
other workers managed by the lb worker.
</li>
</ul>
<p>
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 properties that the lb worker can accept:
</p>
<p>
<b>balanced_workers</b> is a comma separated list of workers that the load balancer
need to manage.
These workers should not appear in the worker.list property.
</p>
<screen>
<note> The worker balance1 while use "real" workers worker1 and worker2</note>
<read>worker.balance1.balanced_workers= worker1, worker2</read>
</screen>
</subsection>
<subsection name="jni Worker properties">
<p>
The jni worker opens a JVM inside the web server process and executes Tomcat within
it (that is in-process).
Following that, messages to and from the JVM are passed using JNI method calls, this
makes the jni worker faster
then the out-of-process workers that need to communicate to the Tomcat workers by
writing AJP messages over
TCP/IP sockets.
</p>
<p>
Note: Since the JVM is multithreaded; the jni worker should be used only within
multithreaded servers
such as AOLServer, IIS, Netscape and Apache 2.0.<br/>
You should also make sure that the threading scheme used by the web servers match
the one
used to build the jk web server plugin.
</p>
<p>
Since the jni worker opens a JVM it can accept many properties that it forward to
the JVM such as
the classpath etc. as we can see in the following table.
</p>
<p>
<b>class_path</b> is the classpath as used by the in-process JVM. This should point
to all Tomcats'
jar/file files as well as any class or other jar file that you want to add to the
JVM.
</p>
<p>
To have JSP compile support, you should remember to also add Javac to the classpath.
This can be done in Java2 by adding tools.jar to the classpath.
In JDK1.xx you should just add classes.zip.
</p>
<p>
The <b>class_path</b> property can be given in multiple lines.
In this case the jk environment will concatenate all the classpath entries together
by putting path delimiter (":"/";") between the entries.
</p>
<screen>
<note>Set the classpath for worker "wrkjni"</note>
<read>worker.wrkjni.class_path=/var/tomcat3/lib/tomcat.jar</read>
<note>we don't forget to add JAVAC (tools.jar)</note>
<read>worker.wrkjni.class_path=/opt/IBMJava2-131/lib/tools.jar</read>
</screen>
<p>
<b>cmd_line</b> is the command line that is handed over to Tomcats' startup code.
</p>
<p>
The cmd_line property can be given in multiple lines.
In this case the jk environment will concatenate all the cmd_line entries together
by putting spaces
between the entries.
</p>
<screen>
<note>Set command line for "wrkjni"</note>
<read>worker.wrkjni.cmd_line=-config</read>
<note>Next arg</note>
<read>worker.wrkjni.cmd_line=/etc/tomcat3/conf/alt-server.xml</read>
<note>Very important tomcat.home</note>
<read>worker.wrkjni.cmd_line=-home</read>
<note>Location of tomcat.home</note>
<read>worker.wrkjni.cmd_line=/var/tomcat3</read>
</screen>
<p>
<b>jvm_lib</b> is the full path to the JVM implementation library.
The jni worker will use this path to load the JVM dynamically.
</p>
<screen>
<note>Set full path for JVM shared lib (IBM SDK on Linux)</note>
<read>worker.wrkjni.jvm_lib=/opt/IBMJava2-131/jre/bin/classic/libjvm.so</read>
<note>Set full path for JVM shared lib (Sun SDK on Windows)</note>
<read>worker.wrkjni.jvm_lib=c:\JDK\1.3.1\jre\bin\classic</read>
</screen>
<p>
<b>stdout</b> is full path to where the JVM write its System.out
</p>
<screen>
<note>Put logs in /var/log/http/jk-jvm-out.log</note>
<read>worker.wrkjni.stdout=/var/log/http/jk-jvm-out.log</read>
</screen>
<p>
<b>stderr</b> is full path to where the JVM write its System.err
</p>
<screen>
<note>Put logs in /var/log/http/jk-jvm-err.log</note>
<read>worker.wrkjni.stderr=/var/log/http/jk-jvm-err.log</read>
</screen>
<p>
<b>sysprops</b> set the Java system properties for the JVM
</p>
<screen>
<note>Told Java to stay in 64m</note>
<read>worker.wrkjni.sysprops=-Xmx64</read>
</screen>
<p>
<b>ld_path</b> set the additional dynamic libraries path (similar in nature to
LD_LIBRARY_PATH)
</p>
<screen>
<note>Told system which library path to be added to access Java Env</note>
<read>worker.wrkjni.ld_path=/opt/IBMJava2-131/jre/bin/</read>
<read>worker.wrkjni.ld_path=/opt/IBMJava2-131/jre/bin/classic</read>
</screen>
<p>
Notes: Under Linux it seems that processes can't update their own LD_LIBRARY_PATH,
so you'll have to update it BEFORE launching the webserver...
</p>
</subsection>
</section>
</document>
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