The Apache Tomcat Servlet/JSP Container

Apache Tomcat 7

Version 7.0.42, Jan 7 2014
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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:

AttributeDescription
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 10000 (10 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 or equal to 0. If not specified, this attribute is set to 2097152 (2 megabytes).

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 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 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 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, 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.

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 and APR/native) all support the following attributes in addition to the common Connector attributes listed above.

WARNING: The NIO connector for AJP is experimental.

AttributeDescription
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.

clientCertProvider

When client certificate information is presented in a form other than instances of java.security.cert.X509Certificate it needs to be converted before it can be used and this property controls which JSSE provider is used to perform the conversion. For example it is used with the AJP connectors, the HTTP APR connector and with the org.apache.catalina.valves.SSLValve.If not specified, the default provider will be used.

connectionLinger

The number of seconds during which the sockets used by this Connector will linger when they are closed. If not specified, the JVM default will be used.

connectionTimeout

The number of milliseconds this Connector will wait, after accepting a connection, for the request URI line to be presented. The default value for AJP protocol connectors is -1 (i.e. infinite).

executor

A reference to the name in an Executor element. If this attribute is set, and the named executor exists, the connector will use the executor, and all the other thread attributes will be ignored. Note that if a shared executor is not specified for a connector then the connector will use a private, internal executor to provide the thread pool.

keepAliveTimeout

The number of milliseconds this Connector will wait for another AJP request before closing the connection. The default value is to use the value that has been set for the connectionTimeout attribute.

maxConnections

The maximum number of connections that the server will accept and process at any given time. When this number has been reached, the server will not accept any more connections until the number of connections falls below this value. The operating system may still accept connections based on the acceptCount setting. Default value varies by connector type. For BIO the default is the value of maxThreads unless an Executor is used in which case the default will be the value of maxThreads from the executor. For NIO the default is 10000. For APR/native, the default is 8192.

Note that for APR/native on Windows, the configured value will be reduced to the highest multiple of 1024 that is less than or equal to maxConnections. This is done for performance reasons.
If set to a value of -1, the maxConnections feature is disabled and connections are not counted.

maxThreads

The maximum number of request processing threads to be created by this Connector, which therefore determines the maximum number of simultaneous requests that can be handled. If not specified, this attribute is set to 200. If an executor is associated with this connector, this attribute is ignored as the connector will execute tasks using the executor rather than an internal thread pool.

minSpareThreads

The minimum number of threads always kept running. If not specified, the default of 10 is used.

packetSize

This attribute sets the maximum AJP packet size in Bytes. The maximum value is 65536. It should be the same as the max_packet_size directive configured for mod_jk. Normally it is not necessary to change the maximum packet size. Problems with the default value have been reported when sending certificates or certificate chains. The default value is 8192. If set to less than 8192 then the setting will ignored and the default value of 8192 used.

processorCache

The protocol handler caches Processor objects to speed up performance. This setting dictates how many of these objects get cached. -1 means unlimited, default is 200. If not using Servlet 3.0 asynchronous processing, a good default is to use the same as the maxThreads setting. If using Servlet 3.0 asynchronous processing, a good default is to use the larger of maxThreads and the maximum number of expected concurrent requests (synchronous and asynchronous).

requiredSecret

Only requests from workers with this secret keyword will be accepted.

tcpNoDelay

If set to true, the TCP_NO_DELAY option will be set on the server socket, which improves performance under most circumstances. This is set to true by default.

threadPriority

The priority of the request processing threads within the JVM. 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.

tomcatAuthentication

If set to true, the authentication will be done in Tomcat. Otherwise, the authenticated principal will be propagated from the native webserver and used for authorization in Tomcat. The default value is true.

Java TCP socket attributes

The BIO and NIO implementation support the following Java TCP socket attributes in addition to the common Connector and HTTP attributes listed above.

AttributeDescription
socket.rxBufSize

(int)The socket receive buffer (SO_RCVBUF) size in bytes. JVM default used if not set.

socket.txBufSize

(int)The socket send buffer (SO_SNDBUF) size in bytes. JVM default used if not set.

socket.tcpNoDelay

(bool)This is equivalent to standard attribute tcpNoDelay.

socket.soKeepAlive

(bool)Boolean value for the socket's keep alive setting (SO_KEEPALIVE). JVM default used if not set.

socket.ooBInline

(bool)Boolean value for the socket OOBINLINE setting. JVM default used if not set.

socket.soReuseAddress

(bool)Boolean value for the sockets reuse address option (SO_REUSEADDR). JVM default used if not set.

socket.soLingerOn

(bool)Boolean value for the sockets so linger option (SO_LINGER). A value for the standard attribute connectionLinger that is >=0 is equivalent to setting this to true. A value for the standard attribute connectionLinger that is <0 is equivalent to setting this to false. Both this attribute and soLingerTime must be set else the JVM defaults will be used for both.

socket.soLingerTime

(int)Value in seconds for the sockets so linger option (SO_LINGER). This is equivalent to standard attribute connectionLinger. Both this attribute and soLingerOn must be set else the JVM defaults will be used for both.

socket.soTimeout

This is equivalent to standard attribute connectionTimeout.

socket.performanceConnectionTime

(int)The first value for the performance settings. See Socket Performance Options All three performance attributes must be set else the JVM defaults will be used for all three.

socket.performanceLatency

(int)The second value for the performance settings. See Socket Performance Options All three performance attributes must be set else the JVM defaults will be used for all three.

socket.performanceBandwidth

(int)The third value for the performance settings. See Socket Performance Options All three performance attributes must be set else the JVM defaults will be used for all three.

socket.unlockTimeout

(int) The timeout for a socket unlock. When a connector is stopped, it will try to release the acceptor thread by opening a connector to itself. The default value is 250 and the value is in milliseconds

NIO specific configuration

The following attributes are specific to the NIO connector.

AttributeDescription
socket.directBuffer

(bool)Boolean value, whether to use direct ByteBuffers or java mapped ByteBuffers. Default is false.
When you are using direct buffers, make sure you allocate the appropriate amount of memory for the direct memory space. On Sun's JDK that would be something like -XX:MaxDirectMemorySize=256m.

socket.appReadBufSize

(int)Each connection that is opened up in Tomcat get associated with a read ByteBuffer. This attribute controls the size of this buffer. By default this read buffer is sized at 8192 bytes. For lower concurrency, you can increase this to buffer more data. For an extreme amount of keep alive connections, decrease this number or increase your heap size.

socket.appWriteBufSize

(int)Each connection that is opened up in Tomcat get associated with a write ByteBuffer. This attribute controls the size of this buffer. By default this write buffer is sized at 8192 bytes. For low concurrency you can increase this to buffer more response data. For an extreme amount of keep alive connections, decrease this number or increase your heap size.
The default value here is pretty low, you should up it if you are not dealing with tens of thousands concurrent connections.

socket.bufferPool

(int)The NIO connector uses a class called NioChannel that holds elements linked to a socket. To reduce garbage collection, the NIO connector caches these channel objects. This value specifies the size of this cache. The default value is 500, and represents that the cache will hold 500 NioChannel objects. Other values are -1 for unlimited cache and 0 for no cache.

socket.bufferPoolSize

(int)The NioChannel pool can also be size based, not used object based. The size is calculated as follows:
NioChannel buffer size = read buffer size + write buffer size
SecureNioChannel buffer size = application read buffer size + application write buffer size + network read buffer size + network write buffer size
The value is in bytes, the default value is 1024*1024*100 (100MB).

socket.processorCache

(int)Tomcat will cache SocketProcessor objects to reduce garbage collection. The integer value specifies how many objects to keep in the cache at most. The default is 500. Other values are -1 for unlimited cache and 0 for no cache.

socket.keyCache

(int)Tomcat will cache KeyAttachment objects to reduce garbage collection. The integer value specifies how many objects to keep in the cache at most. The default is 500. Other values are -1 for unlimited cache and 0 for no cache.

socket.eventCache

(int)Tomcat will cache PollerEvent objects to reduce garbage collection. The integer value specifies how many objects to keep in the cache at most. The default is 500. Other values are -1 for unlimited cache and 0 for no cache.

selectorPool.maxSelectors

(int)The max selectors to be used in the pool, to reduce selector contention. Use this option when the command line org.apache.tomcat.util.net.NioSelectorShared value is set to false. Default value is 200.

selectorPool.maxSpareSelectors

(int)The max spare selectors to be used in the pool, to reduce selector contention. When a selector is returned to the pool, the system can decide to keep it or let it be GC'd. Use this option when the command line org.apache.tomcat.util.net.NioSelectorShared value is set to false. Default value is -1 (unlimited).

command-line-options

The following command line options are available for the NIO connector:
-Dorg.apache.tomcat.util.net.NioSelectorShared=true|false - default is true. Set this value to false if you wish to use a selector for each thread. When you set it to false, you can control the size of the pool of selectors by using the selectorPool.maxSelectors attribute.

APR/native specific configuration

The APR/native implementation supports the following attributes in addition to the common Connector and AJP attributes listed above.

AttributeDescription
pollTime

Duration of a poll call in microseconds. 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 (2ms).

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 8192, corresponding to 8192 keep-alive connections.

Nested Components

None at this time.

Special Features
Proxy Support

The proxyName and proxyPort attributes can be used when Tomcat is run behind a proxy server. These attributes modify the values returned to web applications that call the request.getServerName() and request.getServerPort() methods, which are often used to construct absolute URLs for redirects. Without configuring these attributes, the values returned would reflect the server name and port on which the connection from the proxy server was received, rather than the server name and port to whom the client directed the original request.

For more information, see the Proxy Support HOW-TO.

Connector Comparison

Below is a small chart that shows how the connectors differentiate.

                       Java Blocking Connector   Java Nio Blocking Connector   APR/native Connector
                                 BIO                         NIO                       APR
    Classname                AjpProtocol               AjpNioProtocol           AjpAprProtocol
    Tomcat Version           3.x onwards                 7.x onwards              5.5.x onwards
    Support Polling              NO                          YES                       YES
    Polling Size                 N/A                   maxConnections             maxConnections
    Read Request Headers      Blocking                  Sim Blocking                   Blocking
    Read Request Body         Blocking                  Sim Blocking                   Blocking
    Write Response            Blocking                  Sim Blocking                   Blocking
    Wait for next Request     Blocking                  Non Blocking               Non Blocking
    Max Connections        maxConnections              maxConnections             maxConnections

    
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