Links User Guide Reference Apache Tomcat Development | | Introduction |
Tomcat can use the 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).
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.
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| Installation |
APR support requires three main native components to be installed:
- APR library
- JNI wrappers for APR used by Tomcat (libtcnative)
- OpenSSL libraries
| Windows |
Windows binaries are provided for tcnative-1, which is a statically compiled .dll which includes
OpenSSL and APR. It can be downloaded from 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 Official OpenSSL
website (see related/binaries).
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| APR Components |
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.
When APR is enabled, the following features are also enabled in Tomcat:
- Secure session ID generation by default on all platforms (platforms other than Linux required
random number generation using a configured entropy)
- OS level statistics on memory usage and CPU usage by the Tomcat process are displayed by
the status servlet
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| APR Connectors Configuration |
| HTTP |
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.
The following attributes are supported in the HTTP APR connector in addition to the ones supported
in the regular HTTP connector:
| Attribute | Description |
|---|
firstReadTimeout |
The first read of a request will be made using the specified timeout. If no data is available
after the specified time, the socket will be placed in the poller. Setting this value to 0 will
increase scalability, but will have a minor impact on latency (see the related pollTime attribute).
The default value is 100 (100ms). Note: on Windows, the actual value of firstReadTimeout will
be 500 + the specified value.
| pollTime |
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 5000 (5ms).
| pollerSize |
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 768, corresponding to
768 keepalive connections.
| useSendfile |
Use kernel level sendfile for certain static files. The default value is true.
| sendfileSize |
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 256.
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| HTTPS |
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.
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 Official OpenSSL
website). The SSL specific attributes for the connector are:
| Attribute | Description |
|---|
SSLEngine |
Name of the SSLEngine to use. off: Do not use SSL, on: Use SSL but no specific ENGINE.
The default value is off.
| SSLProtocol |
Protocol which may be used for communicating with clients. The default is "all", with
other acceptable values being "SSLv2", "SSLv3", "TLSv1", and "SSLv2+SSLv3".
| SSLCipherSuite |
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).
| SSLCertificateFile |
Name of the file that contains the server certificate. The format is PEM-encoded.
| SSLCertificateKeyFile |
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).
| SSLPassword |
Pass phrase for the encrypted private key. If "SSLPassword" is not provided, the callback fonction
should prompt for the pass phrase.
| SSLVerifyClient |
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".
| SSLVerifyDepth |
Maximum verification depth for client certificates. The default is "10".
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An example SSL Connector declaration can be:
 | | | |
<Connector port="443" maxHttpHeaderSize="8192"
maxThreads="150" minSpareThreads="25" maxSpareThreads="75"
enableLookups="false" disableUploadTimeout="true"
acceptCount="100" scheme="https" secure="true"
SSLEngine="on"
SSLCertificateFile="${catalina.base}/conf/localhost.crt"
SSLCertificateKeyFile="${catalina.base}/conf/localhost.key" /> | | | | |
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| AJP |
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.
The following attributes are supported in the AJP APR connector in addition to the ones supported
in the regular AJP connector:
| Attribute | Description |
|---|
firstReadTimeout |
The first read of a request will be made using the specified timeout. If no data is available
after the specified time, the socket will be placed in the poller. Setting this value to 0 will
increase scalability, but will have a minor impact on latency (see the related pollTime attribute).
The default value is 100 (100ms). Note: on Windows, the actual value of firstReadTimeout will
be 500 + the specified value.
| pollTime |
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 5000 (5ms).
| pollerSize |
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 768, corresponding to
768 keepalive connections.
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