Tomcat example source code file (apr.xml)
The Tomcat apr.xml source code
<?xml version="1.0"?>
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<!DOCTYPE document [
<!ENTITY project SYSTEM "project.xml">
]>
<document url="apr.html">
&project;
<properties>
<title>Apache Portable Runtime (APR) based Native library for Tomcat
<author>Remy Maucherat
</properties>
<body>
<section name="Introduction">
<p>
Tomcat can use the <a href="http://apr.apache.org/">Apache Portable Runtime to
provide superior scalability, performance, and better integration with native server
technologies. The Apache Portable Runtime is a highly portable library that is at
the heart of Apache HTTP Server 2.x. APR has many uses, including access to advanced IO
functionality (such as sendfile, epoll and OpenSSL), OS level functionality (random number
generation, system status, etc), and native process handling (shared memory, NT
pipes and Unix sockets).
</p>
<p>
These features allows making Tomcat a general purpose webserver, will enable much better
integration with other native web technologies, and overall make Java much more viable as
a full fledged webserver platform rather than simply a backend focused technology.
</p>
</section>
<section name="Installation">
<p>
APR support requires three main native components to be installed:
<ul>
<li>APR library
<li>JNI wrappers for APR used by Tomcat (libtcnative)
<li>OpenSSL libraries
</ul>
</p>
<subsection name="Windows">
<p>
Windows binaries are provided for tcnative-1, which is a statically compiled .dll which includes
OpenSSL and APR. It can be downloaded from <a href="http://tomcat.heanet.ie/native/">here
as 32bit or AMD x86-64 binaries.
In security conscious production environments, it is recommended to use separate shared dlls
for OpenSSL, APR, and libtcnative-1, and update them as needed according to security bulletins.
Windows OpenSSL binaries are linked from the <a href="http://www.openssl.org">Official OpenSSL
website</a> (see related/binaries).
</p>
</subsection>
<subsection name="Linux">
<p>
Most Linux distributions will ship packages for APR and OpenSSL. The JNI wrapper (libtcnative) will
then have to be compiled. It depends on APR, OpenSSL, and the Java headers.
</p>
<p>
Requirements:
<ul>
<li>APR 1.2+ development headers (libapr1-dev package)
<li>OpenSSL 0.9.7+ development headers (libssl-dev package)
<li>JNI headers from Java compatible JDK 1.4+
<li>GNU development environment (gcc, make)
</ul>
</p>
<p>
The wrapper library sources are located in the Tomcat binary bundle, in the
<code>bin/tomcat-native.tar.gz archive.
Once the build environment is installed and the source archive is extracted, the wrapper library
can be compiled using (from the folder containing the configure script):
<source>./configure && make && make install
</p>
</subsection>
</section>
<section name="APR Components">
<p>
Once the libraries are properly installed and available to Java (if loading fails, the library path
will be displayed), the Tomcat connectors will automatically use APR. Configuration of the connectors
is similar to the regular connectors, but have a few extra attributes which are used to configure
APR components. Note that the defaults should be well tuned for most use cases, and additional
tweaking shouldn't be required.
</p>
<p>
When APR is enabled, the following features are also enabled in Tomcat:
<ul>
<li>Secure session ID generation by default on all platforms (platforms other than Linux required
random number generation using a configured entropy)</li>
<li>OS level statistics on memory usage and CPU usage by the Tomcat process are displayed by
the status servlet</li>
</ul>
</p>
</section>
<section name="APR Lifecycle Listener Configuration">
<subsection name="AprLifecycleListener">
<attribute name="SSLEngine" required="false">
<p>
Name of the SSLEngine to use. off: Do not use SSL, on: Use SSL but no specific ENGINE.
The default value is <b>on.
This initializes the native SSL engine, then enable the use of this engine in the connector
using the <code>SSLEnabled attribute. Example:
<source>
<Listener className="org.apache.catalina.core.AprLifecycleListener" SSLEngine="on" />
</source>
</p>
<p>See the Official OpenSSL
website</a> for more details on SSL hardware engines and manufacturers.
</p>
</attribute>
</subsection>
</section>
<section name="APR Connectors Configuration">
<subsection name="HTTP">
<p>
When APR is enabled, the HTTP connector will use sendfile for hadling large static files (all such
files will be sent ansychronously using high performance kernel level calls), and will use
a socket poller for keepalive, increasing scalability of the server.
</p>
<p>
The following attributes are supported in the HTTP APR connector in addition to the ones supported
in the regular HTTP connector:
</p>
<attributes>
<attribute name="keepAliveTimeout" required="false">
<p>The number of milliseconds this Connector will wait for
another HTTP request before closing the connection.
The default value is to use the value that has been set for the
connectionTimeout attribute. This value also controls the timeout interval which
is used for Comet connections.</p>
</attribute>
<attribute name="pollTime" required="false">
<p>Duration of a poll call. Lowering this value will slightly decrease latency of connections
being kept alive in some cases, but will use more CPU as more poll calls are being made. The
default value is 2000 (5ms).</p>
</attribute>
<attribute name="pollerSize" required="false">
<p>Amount of sockets that the poller responsible for polling kept alive connections can hold at a
given time. Extra connections will be closed right away. The default value is 8192, corresponding to
8192 keepalive connections.</p>
</attribute>
<attribute name="useSendfile" required="false">
<p>Use kernel level sendfile for certain static files. The default value is true.
</attribute>
<attribute name="sendfileSize" required="false">
<p>Amount of sockets that the poller responsible for sending static files asynchronously can hold
at a given time. Extra connections will be closed right away without any data being sent
(resulting in a zero length file on the client side). Note that in most cases, sendfile is a call
that will return right away (being taken care of "synchonously" by the kernel), and the sendfile
poller will not be used, so the amount of static files which can be sent concurrently is much larger
than the specified amount. The default value is 1024.</p>
</attribute>
</attributes>
</subsection>
<subsection name="HTTPS">
<p>
When APR is enabled, the HTTPS connector will use a socket poller for keepalive, increasing
scalability of the server. It also uses OpenSSL, which may be more optimized than JSSE depending
on the processor being used, and can be complemented with many commercial accelerator components.
Unlike the HTTP connector, the HTTPS connector cannot use sendfile to optimize static file
processing.
</p>
<p>
The HTTPS APR connector has the same basic attributes than the HTTP APR connector, but adds
OpenSSL specific ones. For the full details on using OpenSSL, please refer to OpenSSL documentations
and the many books available for it (see the <a href="http://www.openssl.org">Official OpenSSL
website</a>). The SSL specific attributes for the connector are:
</p>
<attributes>
<attribute name="SSLEnabled" required="false">
<p>
Enable SSL on the socket, default value is false. Set this value to true
to enable SSL handshake/encryption/decryption in the APR connector.
</p>
</attribute>
<attribute name="SSLProtocol" required="false">
<p>
Protocol which may be used for communicating with clients. The default is "all", with
other acceptable values being "SSLv2", "SSLv3", "TLSv1", and "SSLv2+SSLv3".
</p>
</attribute>
<attribute name="SSLCipherSuite" required="false">
<p>
Ciphers which may be used for communicating with clients. The default is "ALL", with
other acceptable values being a list of ciphers, with ":" used as the delimiter
(see OpenSSL documentation for the list of ciphers supported).
</p>
</attribute>
<attribute name="SSLCertificateFile" required="true">
<p>
Name of the file that contains the server certificate. The format is PEM-encoded.
</p>
</attribute>
<attribute name="SSLCertificateKeyFile" required="false">
<p>
Name of the file that contains the server private key. The format is PEM-encoded.
The default value is the value of "SSLCertificateFile" and in this case both certificate
and private key have to be in this file (NOT RECOMMENDED).
</p>
</attribute>
<attribute name="SSLPassword" required="false">
<p>
Pass phrase for the encrypted private key. If "SSLPassword" is not provided, the callback fonction
should prompt for the pass phrase.
</p>
</attribute>
<attribute name="SSLVerifyClient" required="false">
<p>
Ask client for certificate. The default is "none", meaning the client will not have the opportunity
to submit a certificate. Other acceptable values include "optional", "require" and "optionalNoCA".
</p>
</attribute>
<attribute name="SSLVerifyDepth" required="false">
<p>
Maximum verification depth for client certificates. The default is "10".
</p>
</attribute>
<attribute name="SSLCACertificateFile" required="false">
<p>
See <a href="http://httpd.apache.org/docs/2.2/mod/mod_ssl.html#sslcacertificatefile">the mod_ssl documentation.
</p>
</attribute>
<attribute name="SSLCACertificatePath" required="false">
<p>
See <a href="http://httpd.apache.org/docs/2.2/mod/mod_ssl.html#sslcacertificatepath">the mod_ssl documentation.
</p>
</attribute>
<attribute name="SSLCertificateChainFile" required="false">
<p>
See <a href="http://httpd.apache.org/docs/2.2/mod/mod_ssl.html#sslcertificatechainfile">the mod_ssl documentation.
</p>
</attribute>
<attribute name="SSLCARevocationFile" required="false">
<p>
See <a href="http://httpd.apache.org/docs/2.2/mod/mod_ssl.html#sslcarevocationfile">the mod_ssl documentation.
</p>
</attribute>
<attribute name="SSLCARevocationPath" required="false">
<p>
See <a href="http://httpd.apache.org/docs/2.2/mod/mod_ssl.html#sslcarevocationpath">the mod_ssl documentation.
</p>
</attribute>
</attributes>
<p>
An example SSL Connector declaration can be:
<source>
<Connector port="443" maxHttpHeaderSize="8192"
maxThreads="150" minSpareThreads="25" maxSpareThreads="75"
enableLookups="false" disableUploadTimeout="true"
acceptCount="100" scheme="https" secure="true"
SSLEnabled="true"
SSLCertificateFile="${catalina.base}/conf/localhost.crt"
SSLCertificateKeyFile="${catalina.base}/conf/localhost.key" /></source>
</p>
</subsection>
<subsection name="AJP">
<p>
When APR is enabled, the AJP connector will use a socket poller for keepalive, increasing
scalability of the server. As AJP is designed around a pool of persistent (or almost
persistent) connections, this will reduce significantly the amount of processing threads
needed by Tomcat. Unlike the HTTP connector, the AJP connector cannot use sendfile to optimize
static file processing.
</p>
<p>
The following attributes are supported in the AJP APR connector in addition to the ones supported
in the regular AJP connector:
</p>
<attributes>
<attribute name="pollTime" required="false">
<p>Duration of a poll call. Lowering this value will slightly decrease latency of connections
being kept alive in some cases, but will use more CPU as more poll calls are being made. The
default value is 2000 (5ms).</p>
</attribute>
<attribute name="pollerSize" required="false">
<p>Amount of sockets that the poller responsible for polling kept alive connections can hold at a
given time. Extra connections will be closed right away. The default value is 8192, corresponding to
8192 keepalive connections.</p>
</attribute>
</attributes>
</subsection>
</section>
</body>
</document>
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