## The AJP Connector

### Table of Contents

- Introduction
- Attributes
  1. Common Attributes
  2. Standard Implementations
  3. Java TCP socket attributes
  4. NIO specific configuration
  5. NIO2 specific configuration
  6. APR/native specific configuration
- Nested Components
- Special Features
  1. Proxy Support
  2. Connector Comparison

### 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.

Note: The NIO2 connector is experimental at this time.

### Attributes

#### Common Attributes

All implementations of Connector support the following attributes:

Attribute | Description
--- | ---
`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 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.AjpNio2Protocol` - 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, 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`.
`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.
`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.
`executorTerminationTimeoutMillis` | The time that the private internal executor will wait for request processing threads to terminate before continuing with the process of stopping the connector. If not set, the default is `0` (zero) for the BIO connector and `5000` (5 seconds) for the NIO, NIO2 and APR/native connectors.
`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 accept, but not process, one further connection. This additional connection be blocked until the number of connections being processed falls below maxConnections at which point the server will start accepting and processing new connections again. Note that once the limit has been reached, the operating system may still accept connections based on the `acceptCount` setting. The 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 and NIO2 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, NIO and NIO2 implementation support the following Java TCP socket attributes in addition to the common Connector and HTTP attributes listed above.

Attribute | Description
--- | ---
`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.

Attribute | Description
--- | ---
`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.

#### NIO2 specific configuration

The following attributes are specific to the NIO2 connector.

Attribute | Description
--- | ---
`useCaches` | (bool)Use this attribute to enable or disable object caching to reduce the amount of GC objects produced. The default value is `false`.
`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.bufferPoolSize` | (int)The NIO2 connector uses a class called Nio2Channel 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 Nio2Channel objects. Other values are `-1` for unlimited cache and `0` for no cache.
`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.socketWrapperCache` | (int)Tomcat will cache SocketWrapper 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.

#### APR/native specific configuration

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

Attribute | Description
--- | ---
`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 BIO | Java Nio Blocking Connector NIO | Java Nio2 Blocking Connector NIO2 | APR/native Connector APR
--- | --- | --- | --- | ---
Classname | `AjpProtocol` | `AjpNioProtocol` | `AjpNio2Protocol` | `AjpAprProtocol`
Tomcat Version | 3.x onwards | 7.x onwards | 8.x onwards | 5.5.x onwards
Support Polling | NO | YES | YES | YES
Polling Size | N/A | `maxConnections` | `maxConnections` | `maxConnections`
Read Request Headers | Blocking | Sim Blocking | Blocking | Blocking
Read Request Body | Blocking | Sim Blocking | Blocking | Blocking
Write Response | Blocking | Sim Blocking | Blocking | Blocking
Wait for next Request | Blocking | Non Blocking | Non Blocking | Non Blocking
Max Connections | `maxConnections` | `maxConnections` | `maxConnections` | `maxConnections`

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