The AJP Connector

Table of Contents

Introduction

The AJP Connector element represents a Connector component that communicates with a web connector via the AJP protocol. This is used for cases where you wish to invisibly integrate Tomcat into an existing (or new) Apache installation, and you want Apache to handle the static content contained in the web application, and/or utilize Apache's SSL processing.

This connector supports load balancing when used in conjunction with the jvmRoute attribute of the Engine.

The native connectors supported with this Tomcat release are:

  • JK 1.2.x with any of the supported servers. See the JK docs for details.
  • mod_proxy on Apache httpd 2.x (included by default in Apache HTTP Server 2.2), with AJP enabled: see the httpd docs for details.

Other native connectors supporting AJP may work, but are no longer supported.

Attributes

Common Attributes

All implementations of Connector support the following attributes:

Attribute Description
ajpFlush

A boolean value which can be used to enable or disable sending AJP flush messages to the fronting proxy whenever an explicit flush happens. The default value is true.
An AJP flush message is a SEND_BODY_CHUNK packet with no body content. Proxy implementations like mod_jk or mod_proxy_ajp will flush the data buffered in the web server to the client when they receive such a packet. Setting this to false can reduce AJP packet traffic but might delay sending packets to the client. At the end of the response, AJP does always flush to the client.

allowTrace

A boolean value which can be used to enable or disable the TRACE HTTP method. If not specified, this attribute is set to false.

asyncTimeout

The default timeout for asynchronous requests in milliseconds. If not specified, this attribute is set to the Servlet specification default of 30000 (30 seconds).

enableLookups

Set to true if you want calls to request.getRemoteHost() to perform DNS lookups in order to return the actual host name of the remote client. Set to false to skip the DNS lookup and return the IP address in String form instead (thereby improving performance). By default, DNS lookups are disabled.

maxHeaderCount

The maximum number of headers in a request that are allowed by the container. A request that contains more headers than the specified limit will be rejected. A value of less than 0 means no limit. If not specified, a default of 100 is used.

maxParameterCount

The maximum number of parameter and value pairs (GET plus POST) which will be automatically parsed by the container. Parameter and value pairs beyond this limit will be ignored. A value of less than 0 means no limit. If not specified, a default of 10000 is used. Note that FailedRequestFilter filter can be used to reject requests that hit the limit.

maxPostSize

The maximum size in bytes of the POST which will be handled by the container FORM URL parameter parsing. The limit can be disabled by setting this attribute to a value less than zero. If not specified, this attribute is set to 2097152 (2 megabytes). Note that the FailedRequestFilter can be used to reject requests that exceed this limit.

maxSavePostSize

The maximum size in bytes of the POST which will be saved/buffered by the container during FORM or CLIENT-CERT authentication. For both types of authentication, the POST will be saved/buffered before the user is authenticated. For CLIENT-CERT authentication, the POST is buffered for the duration of the SSL handshake and the buffer emptied when the request is processed. For FORM authentication the POST is saved whilst the user is re-directed to the login form and is retained until the user successfully authenticates or the session associated with the authentication request expires. The limit can be disabled by setting this attribute to -1. Setting the attribute to zero will disable the saving of POST data during authentication. If not specified, this attribute is set to 4096 (4 kilobytes).

parseBodyMethods

A comma-separated list of HTTP methods for which request bodies will be parsed for request parameters identically to POST. This is useful in RESTful applications that want to support POST-style semantics for PUT requests. Note that any setting other than POST causes Tomcat to behave in a way that goes against the intent of the servlet specification. The HTTP method TRACE is specifically forbidden here in accordance with the HTTP specification. The default is POST

port

The TCP port number on which this Connector will create a server socket and await incoming connections. Your operating system will allow only one server application to listen to a particular port number on a particular IP address. If the special value of 0 (zero) is used, then Tomcat will select a free port at random to use for this connector. This is typically only useful in embedded and testing applications.

protocol

Sets the protocol to handle incoming traffic. To configure an AJP connector this must be specified. If no value for protocol is provided, an HTTP connector rather than an AJP connector will be configured.
The standard protocol value for an AJP connector is AJP/1.3 which uses an auto-switching mechanism to select either a Java NIO based connector or an APR/native based connector. If the PATH (Windows) or LD_LIBRARY_PATH (on most unix systems) environment variables contain the Tomcat native library, the native/APR connector will be used. If the native library cannot be found, the Java NIO based connector will be used.
To use an explicit protocol rather than rely on the auto-switching mechanism described above, the following values may be used:
org.apache.coyote.ajp.AjpProtocol - blocking Java connector
org.apache.coyote.ajp.AjpNioProtocol - non blocking Java NIO connector.
org.apache.coyote.ajp.AjpNio2Protocol - non blocking Java NIO2 connector.
org.apache.coyote.ajp.AjpAprProtocol - the APR/native connector.
Custom implementations may also be used.
Take a look at our Connector Comparison chart.

proxyName

If this Connector is being used in a proxy configuration, configure this attribute to specify the server name to be returned for calls to request.getServerName(). See Proxy Support for more information.

proxyPort

If this Connector is being used in a proxy configuration, configure this attribute to specify the server port to be returned for calls to request.getServerPort(). See Proxy Support for more information.

redirectPort

If this Connector is supporting non-SSL requests, and a request is received for which a matching <security-constraint> requires SSL transport, Catalina will automatically redirect the request to the port number specified here.

scheme

Set this attribute to the name of the protocol you wish to have returned by calls to request.getScheme(). For example, you would set this attribute to "https" for an SSL Connector. The default value is "http".

secure

Set this attribute to true if you wish to have calls to request.isSecure() to return true for requests received by this Connector. You would want this on an SSL Connector or a non SSL connector that is receiving data from a SSL accelerator, like a crypto card, a SSL appliance or even a webserver. The default value is false.

URIEncoding

This specifies the character encoding used to decode the URI bytes, after %xx decoding the URL. If not specified, UTF-8 will be used unless the org.apache.catalina.STRICT_SERVLET_COMPLIANCE system property is set to true in which case ISO-8859-1 will be used.

useBodyEncodingForURI

This specifies if the encoding specified in contentType should be used for URI query parameters, instead of using the URIEncoding. This setting is present for compatibility with Tomcat 4.1.x, where the encoding specified in the contentType, or explicitly set using Request.setCharacterEncoding method was also used for the parameters from the URL. The default value is false.

Notes: See notes on this attribute in HTTP Connector documentation.

useIPVHosts

Set this attribute to true to cause Tomcat to use the IP address passed by the native web server to determine the Host to send the request to. The default value is false.

xpoweredBy

Set this attribute to true to cause Tomcat to advertise support for the Servlet specification using the header recommended in the specification. The default value is false.

Standard Implementations

To use AJP, you must specify the protocol attribute (see above).

The standard AJP connectors (BIO, NIO, NIO2 and APR/native) all support the following attributes in addition to the common Connector attributes listed above.

Attribute Description
acceptCount

The maximum queue length for incoming connection requests when all possible request processing threads are in use. Any requests received when the queue is full will be refused. The default value is 100.

acceptorThreadCount

The number of threads to be used to accept connections. Increase this value on a multi CPU machine, although you would never really need more than 2. Also, with a lot of non keep alive connections, you might want to increase this value as well. Default value is 1.

acceptorThreadPriority

The priority of the acceptor threads. The threads used to accept new connections. The default value is 5 (the value of the java.lang.Thread.NORM_PRIORITY constant). See the JavaDoc for the java.lang.Thread class for more details on what this priority means.

address

For servers with more than one IP address, this attribute specifies which address will be used for listening on the specified port. By default, this port will be used on all IP addresses associated with the server. A value of 127.0.0.1 indicates that the Connector will only listen on the loopback interface.

bindOnInit

Controls when the socket used by the connector is bound. By default it is bound when the connector is initiated and unbound when the connector is destroyed. If set to false, the socket will be bound when the connector is started and unbound when it is stopped.