The Apache Tomcat Connectors - Reference Guide (1.2.50) - Configuring mod_jk for the Apache HTTP Server
Author: Mladen Turk

## Configuring mod_jk for the Apache HTTP Server

### Configuration Directives

Most of the directives are allowed once in the global part of the Apache HTTP Server configuration and once in every <VirtualHost> elements. Exceptions from this rule are explicitly listed in the table below.

Most values are inherited from the main server to the virtual hosts. Since version 1.2.20 they can be overwritten in the virtual hosts. Exceptions from this rule are again explicitly listed in the table below. See especially JkMountCopy.

Warning: If Apache and Tomcat are configured to serve content from the same file system location then care must be taken to ensure that Apache is not able to serve inappropriate content such as the contents of the WEB-INF directory or JSP source code.

This could occur if the Apache DocumentRoot overlaps with a Tomcat Host's appBase or the docBase of any Context. It could also occur when using the Apache Alias directive with a Tomcat Host's appBase or the docBase of any Context.

Here are the all directives supported by Apache:

Attribute | Description
--- | ---
`JkWorkersFile` | The name of a worker file for the Tomcat servlet containers. This directive is only allowed once. It must be put into the global part of the configuration. If you don't use the JkWorkerProperty directives, then you must define your workers with a valid JkWorkersFile. There is no default value.
`JkWorkerProperty` | Enables setting worker properties inside Apache configuration file. The syntax is the same as in the JkWorkersFile (usually workers.properties). Simply prefix each line with "JkWorkerProperty" to put it directly into the Apache config files. This directive is allowed multiple times. It must be put into the global part of the configuration. If you don't use the JkWorkerProperty directives, then you must define your workers with a valid JkWorkersFile. There is no default value. This directive is available in jk1.2.7 version and later.
`JkShmFile` | Shared memory file name. Used only on unix platforms. The shm file is used by balancer and status workers. This directive is only allowed once. It must be put into the global part of the configuration. The default value is logs/jk-runtime-status. It is highly recommended that the shm file be placed on a local drive and not an NFS share. The shared memory contains configuration and runtime information for load balancer workers and their members. It is need in order that all Apache children share the same status information for load balancing members (OK, ERROR, ...), share the information about load taken by the individual workers, share the information for the parts of the configuration, which are changeable during runtime by status workers.
`JkShmSize` | Size of the shared memory file name. This directive is only allowed once. It must be put into the global part of the configuration. The default value depends on the platform. It is usually less than 64KB.
`JkMountFile` | File containing multiple mappings from a context to a Tomcat worker. It is usually called uriworkermap.properties. For inheritance rules, see: JkMountCopy. There is no default value.
`JkMountFileReload` | This directive configures the reload check interval in seconds. The JkMountFile is checked periodically for changes. A changed file gets reloaded automatically. If you set this directive to "0", reload checking is turned off. The default value is 60 seconds. This directive has been added in version 1.2.20 of mod_jk.
`JkMount` | A mount point from a context to a Tomcat worker. This directive is allowed multiple times. It is allowed in the global configuration and in VirtualHost. You can also use it inside Location with a different syntax. Inside Location, one omits the first argument (path), which gets inherited verbatim from the Location argument. Whereas <Location /myapp> matches any URI beginning with "/myapp", any JkMount nested in such a Location block will only match for requests with exact URI /myapp. Therefore nesting JkMount in Location is typically not the right thing to do. By default JkMount entries are not inherited from the global server to other VirtualHosts or between VirtualHosts. For the complete inheritance rules, see: JkMountCopy. You might append rule extensions to the worker name. The extensions are separated from the worker name by a semicolon ";" using the same syntax as in the uriworkermap.properties file.
`JkUnMount` | An exclusion mount point from a context to a Tomcat worker. All exclusion mounts are checked after mapping a request to a tomcat worker. If the request maps also to an exclusion, it will not be forwarded to tomcat, and instead be served locally. This directive is allowed multiple times. It is allowed in the global configuration and in VirtualHost. You can also use it inside Location with a different syntax. Inside Location, one omits the first argument (path), which gets inherited verbatim from the Location argument. Whereas <Location /myapp> matches any URI beginning with "/myapp", any JkUnMount nested in such a Location block will only match for requests with exact URI /myapp. Therefore nesting JkUnMount in Location is typically not the right thing to do. For inheritance rules, see: JkMountCopy. This directive is available in jk1.2.7 version and later.
`JkAutoAlias` | Automatically Alias webapp context directories into the Apache document space. Care should be taken to ensure that only static content is served via Apache as a result of using this directive. Any static content served by Apache will bypass any security constraints defined in the application's web.xml. For inheritance rules, see: JkMountCopy. There is no default value.
`JkMountCopy` | If this directive is set to "On" in some virtual server, the mounts from the global server will be copied to this virtual server, more precisely all mounts defined by JkMount or JkUnMount. The Mounts defined by JkMountFile and JkAutoAlias will only be inherited, if the VirtualHost does not define it's own JkMountFile or JkAutoAlias. If you want all vhost to inherit mounts from the main server, you can set JkMountCopy to 'All' in the main server. This directive is only allowed inside VirtualHost (with value "On") and in the global server (with value "All"). The default is Off, so no mounts will be inherited from the global server to any VirtualHost. Starting with version 1.2.26 you can also set it to "All" in the global virtual server. This will switch the default to On.
`JkWorkerIndicator` | Name of the Apache environment variable that can be used to set worker names in combination with SetHandler jakarta-servlet. This directive is only allowed once per virtual server. It is allowed in the global configuration and in VirtualHost. The default value is JK_WORKER_NAME.
`JkWatchdogInterval` | This directive configures the watchdog thread interval in seconds. The workers are maintained periodically by a background thread running periodically every watchdog_interval seconds. Worker maintenance checks for idle connections, corrects load status and is able to detect backend health status. The maintenance only happens, if since the last maintenance at least `worker.maintain` seconds have passed. So setting the JkWatchdogInterval much smaller than `worker.maintain` is not useful. The default value is 0 seconds, meaning the watchdog thread will not be created, and the maintenance is done in combination with normal requests instead. This directive is only allowed once. It must be put into the global part of the configuration. This directive has been added in version 1.2.27 of mod_jk. It is available only for Apache 2.x and above using APR libraries including thread support.
`JkLogFile` | Full or server relative path to the mod_jk log file. It will also work with pipe, by using a value of the form "| ...". The default value is logs/mod_jk.log. Pipes are supported for Apache 1.3 only since version 1.2.16. The default value exists only since version 1.2.20.
`JkLogLevel` | The mod_jk log level, can be debug, info, warn error or trace. The default value is info.
`JkLogStampFormat` | The mod_jk date log format, using an extended strftime syntax. This format will be used for the time stamps in the JkLogFile. The maximum length of the format is 63 characters. Starting with version 1.2.24 of mod_jk you can also use %Q for adding milliseconds to the log and %q for microseconds. These conversion specifiers are an extension to strftime. They will only work on platforms with a gettimeofday() function. You can use %Q and %q only once in the pattern and also not both together in the same pattern. The default value is "[%a %b %d %H:%M:%S %Y] " and beginning with version 1.2.24 on platforms with a gettimeofday() function it is "[%a %b %d %H:%M:%S.%Q %Y] ".
`JkRequestLogFormat` | Request log format string. See detailed description below. There is no default value. Without defining a value, the request logging is turned off.
`JkExtractSSL` | Turns on SSL processing and information gathering by mod_jk The default value is On. In order to make SSL data available for mod_jk in Apache, you need to set `SSLOptions +StdEnvVars`. For the certificate information you also need to add `SSLOptions +ExportCertData`. Specifically, mod_jk will export the following environment variables from Apache to Tomcat under these request attributes as per the Servlet Specification 3.0, section 3.8:
Env Var | Request Attribute Name | Type | Example
--- | --- | --- | ---
SSL_CIPHER (or `JkKEYSIZEIndicator`) | javax.servlet.request.cipher_suite | java.lang.String | DHE-RSA-AES256-SHA
SSL_CIPHER_USEKEYSIZE (or `JkKEYSIZEIndicator`) | javax.servlet.request.key_size | java.lang.Integer | 256
SSL_SESSION_ID (or `JkSESSIONIndicator`) | javax.servlet.request.ssl_session | java.lang.String | 905...32E (a hex string)
SSL_CLIENT_CERT_CHAIN_n (or `JkCERTCHAINPrefix`n) | javax.servlet.request.X509Certificate | java.security.X509Certificate[] | (A chain of certs in ascending order of trust, the first one being ths client's certificate, the second being the signer of that certificate, and so on)
In addition mod_jk sends the name of the SSL protocol used as a proprietary request attribute named `AJP_SSL_PROTOCOL`. Modern Tomcat versions will expose this attribute under the name `org.apache.tomcat.util.net.secure_protocol_version`. This feature has been added in version 1.2.41 of mod_jk. See also JkSSLPROTOCOLIndicator. For all other SSL-related variables, use `JkEnvVar` for each variable you want. Please note that, like `JkEnvVar`, these variables are available from the request attributes, not as environment variables or as request headers.
`JkRequestIdIndicator` | Name of the Apache environment variable that contains a unique request id. The value of the environment variable will be added to most mod_jk error log lines and allows easy correlation with Apache logs by adding that environment variable there as well. The default value is "UNIQUE_ID". Loading the module "mod_unique_id" will automatically provide a unique request id under that name. This feature has been added in version 1.2.49 of mod_jk. If a request id is sent by the client or another reverse proxy in front via an HTTP request header, one can make this id available for mod_jk by copying it to an environment variable using mod_setenvif: `SetEnvIf X-REQUEST-ID-HEADER "(.+)" X-REQUEST-ID=$1` copies the value of the incoming header `X-REQUEST-ID-HEADER` to the environment variable `X-REQUEST-ID`. mod_jk can pick it up from there via `JkRequestIdIndicator X-REQUEST-ID`.
`JkHTTPSIndicator` | Name of the Apache environment variable that contains SSL indication. The default value is "HTTPS".
`JkSSLPROTOCOLIndicator` | Name of the Apache environment variable that contains the SSL protocol name. The default value is "SSL_PROTOCOL". This directive has been added in version 1.2.41 of mod_jk.
`JkCERTSIndicator` | Name of the Apache environment variable that contains SSL client certificates. The default value is "SSL_CLIENT_CERT".
`JkCIPHERIndicator` | Name of the Apache environment variable that contains SSL client cipher. The default value is "SSL_CIPHER".
`JkCERTCHAINPrefix` | Name of the Apache environment (prefix) that contains SSL client chain certificates. The default value is "SSL_CLIENT_CERT_CHAIN_".
`JkSESSIONIndicator` | Name of the Apache environment variable that contains SSL session. The default value is "SSL_SESSION_ID".
`JkKEYSIZEIndicator` | Name of the Apache environment variable that contains SSL key size in use. The default value is "SSL_CIPHER_USEKEYSIZE".
`JkLocalNameIndicator` | Name of the Apache environment variable which can be used to overwrite the forwarded local name. Use this only if you need to adjust the data (see the proxy documentation). The default value is "JK_LOCAL_NAME". This directive has been added in version 1.2.28 of mod_jk.
`JkIgnoreCLIndicator` | Name of the Apache environment variable which forces to ignore an existing Content-Length request header. This can be used to make mod_jk conpatible with mod_deflate request body inflation (see below). The default value is "JK_IGNORE_CL". This directive has been added in version 1.2.41 of mod_jk.
`JkLocalAddrIndicator` | Name of the Apache environment variable which can be used to overwrite the forwarded local IP address. Use this only if you need to adjust the data (see the proxy documentation). The default value is "JK_LOCAL_ADDR". This directive has been added in version 1.2.41 of mod_jk.
`JkLocalPortIndicator` | Name of the Apache environment variable which can be used to overwrite the forwarded local port. Use this only if you need to adjust the data (see the proxy documentation). The default value is "JK_LOCAL_PORT". This directive has been added in version 1.2.28 of mod_jk.
`JkRemoteHostIndicator` | Name of the Apache environment variable which can be used to overwrite the forwarded remote (client) host name. Use this only if you need to adjust the data (see the proxy documentation). The default value is "JK_REMOTE_HOST". This directive has been added in version 1.2.28 of mod_jk.
`JkRemoteAddrIndicator` | Name of the Apache environment variable which can be used to overwrite the forwarded remote (client) IP address. Use this only if you need to adjust the data (see the proxy documentation). The default value is "JK_REMOTE_ADDR". This directive has been added in version 1.2.28 of mod_jk.
`JkRemotePortIndicator` | Name of the Apache environment variable which can be used to overwrite the forwarded remote (client) IP address. Use this only if you need to adjust the data (see the proxy documentation). The default value is "JK_REMOTE_PORT". This directive has been added in version 1.2.32 of mod_jk.
`JkRemoteUserIndicator` | Name of the Apache environment variable which can be used to overwrite the forwarded user name. Use this only if you need to adjust the data (see the proxy documentation). The default value is "JK_REMOTE_USER". This directive has been added in version 1.2.28 of mod_jk.
`JkAuthTypeIndicator` | Name of the Apache environment variable which can be used to overwrite the forwarded authentication type. Use this only if you need to adjust the data (see the proxy documentation). The default value is "JK_AUTH_TYPE". This directive has been added in version 1.2.28 of mod_jk.
`JkOptions` | Set one of more options to configure the mod_jk module. See below for details about this directive. This directive can be used multiple times per virtual server. The default value is "ForwardURIProxy" since version 1.2.24. It was "ForwardURICompatUnparsed" in version 1.2.23 and "ForwardURICompat" until version 1.2.22.
`JkEnvVar` | Adds a name and an optional default value of environment variable that should be sent to servlet-engine as a request attribute. If the default value is not given explicitly, the variable will only be send, if it is set during runtime. The default is empty, so no additional variables will be sent. This directive can be used multiple times per virtual server. The settings will be merged between the global server and any virtual server. You can retrieve the variables on Tomcat as request attributes via request.getAttribute(attributeName). Note that the variables send via JkEnvVar will not be listed in request.getAttributeNames(). Empty default values are supported since version 1.2.20. Not sending variables with empty defaults and empty runtime value has been introduced in version 1.2.21.
`JkStripSession` | If this directive is set to On in some virtual server, the session IDs `;jsessionid=...` will be removed for URLs which are not forwarded but instead are handled by the local server. This directive is only allowed inside VirtualHost. The default is Off. This directive has been introduced in version 1.2.21. With version 1.2.27 and later this directive can have optional session ID identifier. If not specified it defaults to `;jsessionid`.

### Configuration Directives Types

We'll discuss here the mod_jk directive types.

#### Define workers

JkWorkersFile specify the location where mod_jk will find the workers definitions. Take a look at Workers documentation for detailed description.

    JkWorkersFile     /etc/httpd/conf/workers.properties

#### Logging

JkLogFile specify the location where mod_jk is going to place its log file.

    JkLogFile     /var/log/httpd/mod_jk.log

Since JK 1.2.3 for Apache 2.x and JK 1.2.16 for Apache 1.3 this can also be used for piped logging:

    JkLogFile     "|/usr/bin/rotatelogs /var/log/httpd/mod_jk.log 86400"

JkLogLevel set the log level between:

- info log will contain standard mod_jk activity (default).
- warn log will contain non fatal error reports.
- error log will contain also error reports.
- debug log will contain all information on mod_jk activity
- trace log will contain all tracing information on mod_jk activity

    JkLogLevel    info

`info` should be your default selection for normal operations.

JkLogStampFormat will configure the date/time format found on mod_jk log file. See above for details.

    JkLogStampFormat "[%Y-%m-%d %H:%M:%S.%Q] "

You can log mod_jk information using the Apache standard module mod_log_config. The module sets several notes in the Apache notes table. Most of them are are only useful in combination with a load balancer worker.

Attribute | Description
--- | ---
`JK_WORKER_NAME` | Name of the worker selected by the URI mapping
`JK_WORKER_TYPE` | Type of the worker selected by the URI mapping
`JK_WORKER_ROUTE` | Actual worker name selected by the URI mapping (usually a member of the load balancer). Before version 1.2.26 only available if JkRequestLogFormat is set.
`JK_REQUEST_DURATION` | Request duration in seconds and microseconds. Before version 1.2.26 only available if JkRequestLogFormat is set.
`JK_LB_FIRST_NAME` | Load balancer: Name of the first worker tried
`JK_LB_FIRST_TYPE` | Load balancer: Type of the first worker tried
`JK_LB_FIRST_ACCESSED` | Load balancer: Access count for the first worker tried
`JK_LB_FIRST_SESSIONS` | Load balancer: Count of created sessions for the first worker tried
`JK_LB_FIRST_READ` | Load balancer: Bytes read for the first worker tried
`JK_LB_FIRST_TRANSFERRED` | Load balancer: Bytes transferred for the first worker tried
`JK_LB_FIRST_ERRORS` | Load balancer: Error count for the first worker tried
`JK_LB_FIRST_BUSY` | Load balancer: Busy count for the first worker tried
`JK_LB_FIRST_ACTIVATION` | Load balancer: Activation state for the first worker tried
`JK_LB_FIRST_STATE` | Load balancer: Error state for the first worker tried
`JK_LB_LAST_NAME` | Load balancer: Name of the last worker tried
`JK_LB_LAST_TYPE` | Load balancer: Type of the last worker tried
`JK_LB_LAST_ACCESSED` | Load balancer: Access count for the last worker tried
`JK_LB_LAST_SESSIONS` | Load balancer: Count of created sessions for the last worker tried
`JK_LB_LAST_READ` | Load balancer: Bytes read for the last worker tried
`JK_LB_LAST_TRANSFERRED` | Load balancer: Bytes transferred for the last worker tried
`JK_LB_LAST_ERRORS` | Load balancer: Error count for the last worker tried
`JK_LB_LAST_BUSY` | Load balancer: Busy count for the last worker tried
`JK_LB_LAST_ACTIVATION` | Load balancer: Activation state for the last worker tried
`JK_LB_LAST_STATE` | Load balancer: Error state for the last worker tried

    LogFormat     "%h %l %u %t \"%r\" %>s %b %{JK_WORKER_NAME}n %{JK_LB_FIRST_NAME}n \
                   %{JK_LB_FIRST_BUSY}n %{JK_LB_LAST_NAME}n %{JK_LB_LAST_BUSY}n" mod_jk_log
    CustomLog     logs/access_log     mod_jk_log

You can also log a request protocol in the mod_jk log file instead of the access log. This is not recommended and mostly a backward compatibility feature. The directive JkRequestLogFormat will configure the format of this protocol. It gets configured and enabled on a per virtual host basis. To enable request logging for a virtual host just add a JkRequestLogFormat config. The syntax of the format string is similar to the Apache LogFormat command, here is a list of the available request log format options:

Attribute | Description
--- | ---
`%b` | Bytes sent, excluding HTTP headers (CLF format)
`%B` | Bytes sent, excluding HTTP headers
`%H` | The request protocol
`%m` | The request method
`%p` | The canonical Port of the server serving the request
`%q` | The query string (prepended with a ? if a query string exists, otherwise an empty string)
`%r` | First line of request
`%s` | Request HTTP status code
`%T` | Request duration, elapsed time to handle request in seconds '.' micro seconds
`%U` | The URL path requested, not including any query string.
`%v` | The canonical ServerName of the server serving the request
`%V` | The server name according to the UseCanonicalName setting
`%w` | Tomcat worker name
`%R` | Real worker name

    JkRequestLogFormat     "%w %V %T"

#### Forwarding

The directive JkOptions allow you to set many forwarding options which will enable (+) or disable (-) following option. Without any leading signs, options will be enabled.

The four following options +ForwardURIxxx are mutually exclusive. Exactly one of them is required, a negative sign prefix is not allowed with them. The default value is "ForwardURIProxy" since version 1.2.24. It was "ForwardURICompatUnparsed" in version 1.2.23 and "ForwardURICompat" until version 1.2.22. You can turn the default off by switching on one of the other two options. You should leave this at it's default value, unless you have a very good reason to change it.

All options are inherited from the global server to virtual hosts. Options that support enabling (plus options) and disabling (minus options), are inherited in the following way:
options(vhost) = plus_options(global) - minus_options(global) + plus_options(vhost) - minus_options(vhost)

Using JkOptions ForwardURIProxy, the forwarded URI will be partially reencoded after processing inside Apache and before forwarding to Tomcat. This will be compatible with local URL manipulation by mod_rewrite and with URL encoded session ids.

    JkOptions     +ForwardURIProxy

Using JkOptions ForwardURICompatUnparsed, the forwarded URI will be unparsed. It's spec compliant and secure. It will always forward the original request URI, so rewriting URIs with mod_rewrite and then forwarding the rewritten URI will not work.

    JkOptions     +ForwardURICompatUnparsed

Using JkOptions ForwardURICompat, the forwarded URI will be decoded by Apache. Encoded characters will be decoded and explicit path components like ".." will already be resolved. This is less spec compliant and is not safe if you are using prefix JkMount. This option will allow to rewrite URIs with mod_rewrite before forwarding.

    JkOptions     +ForwardURICompat

Using JkOptions ForwardURIEscaped, the forwarded URI will be the encoded form of the URI used by ForwardURICompat. Explicit path components like ".." will already be resolved. This will not work in combination with URL encoded session IDs, but it will allow to rewrite URIs with mod_rewrite before forwarding.

    JkOptions     +ForwardURIEscaped

JkOptions RejectUnsafeURI will block all URLs, which contain percent signs '%' or backslashes '\' after decoding.

Most web apps do not use such URLs. Using the option RejectUnsafeURI, you can block several well known URL encoding attacks. By default, this option is not set.

You can also realise such a check with mod_rewrite, which is more powerful but also slightly more complicated.

    JkOptions     +RejectUnsafeURI

JkOptions CollapseSlashesAll is deprecated as of 1.2.44 and will be ignored if used.

JkOptions CollapseSlashesUnmount is deprecated as of 1.2.44 and will be ignored if used.

JkOptions CollapseSlashesNone is deprecated as of 1.2.44 and will be ignored if used.

JkOptions ForwardDirectories is used in conjunction with DirectoryIndex directive of Apache. As such mod_dir should be available to Apache, statically or dynamically (DSO)

When DirectoryIndex is configured, Apache will create sub-requests for each of the local-url's specified in the directive, to determine if there is a local file that matches (this is done by stat-ing the file).

If ForwardDirectories is set to false (default) and Apache doesn't find any files that match, Apache will serve the content of the directory (if directive Options specifies Indexes for that directory) or a `403 Forbidden` response (if directive Options doesn't specify Indexes for that directory).

If ForwardDirectories is set to true and Apache doesn't find any files that match, the request will be forwarded to Tomcat for resolution. This is used in cases when Apache cannot see the index files on the file system for various reasons: Tomcat is running on a different machine, the JSP file has been precompiled etc.

Note that locally visible files will take precedence over the ones visible only to Tomcat (i.e. if Apache can see the file, that's the one that's going to get served). This is important if there is more then one type of file that Tomcat normally serves - for instance Velocity pages and JSP pages.

    JkOptions     +ForwardDirectories

Setting JkOptions ForwardLocalAddress, you ask mod_jk to send the local address, of the Apache HTTP Server instead remote client address. This can be used by the Tomcat remote address valve for allowing connections only from configured Apache servers.

    JkOptions     +ForwardLocalAddress

Setting JkOptions ForwardPhysicalAddress, you ask mod_jk to send the physical peer TCP IP address as the client address. By default mod_jk uses the logical address as provided by the web server. For example the module mod_remoteip sets the logical IP address to the client IP forwarded by proxies in the `X-Forwarded-For` header.

    JkOptions     +ForwardPhysicalAddress

JkOptions FlushPackets, you ask mod_jk to flush Apache's connection buffer after each AJP packet chunk received from Tomcat. This option can have a strong performance penalty for Apache and Tomcat as writes are performed more often than would normally be required (ie: at the end of each response).

    JkOptions     +FlushPackets

JkOptions FlushHeader, you ask mod_jk to flush Apache's connection buffer after the response headers have been received from Tomcat.

    JkOptions     +FlushHeader

JkOptions DisableReuse, you ask mod_jk to close connections immediately after their use. Normally mod_jk uses persistent connections and pools idle connections to reuse them, when new requests have to be sent to Tomcat.

Using this option will have a strong performance penalty for Apache and Tomcat. Use this only as a last resort in case of unfixable network problems. If a firewall between Apache and Tomcat silently kills idle connections, try to use the worker attribute socket_keepalive in combination with an appropriate TCP keepalive value in your OS.

    JkOptions     +DisableReuse

JkOptions ForwardKeySize, you ask mod_jk, when using ajp13, to forward also the SSL Key Size as required by Servlet API 2.3. This flag shouldn't be set when servlet engine is Tomcat 3.2.x (on by default).

    JkOptions     +ForwardKeySize

JkOptions ForwardSSLCertChain, you ask mod_jk, when using ajp13, to forward SSL certificate chain (off by default). Mod_jk only passes the `SSL_CLIENT_CERT` to the AJP connector. This is not a problem with self-signed certificates or certificates directly signed by the root CA certificate. However, there's a large number of certificates signed by an intermediate CA certificate, where this is a significant problem: A servlet will not have the possibility to validate the client certificate on its own. The bug would be fixed by passing on the `SSL_CLIENT_CERT_CHAIN` to Tomcat via the AJP connector.
This directive exists only since version 1.2.22.

    JkOptions     +ForwardSSLCertChain

The directive JkEnvVar allows you to forward environment variables from Apache server to Tomcat engine. You can add a default value as a second parameter to the directive. If the default value is not given explicitly, the variable will only be send, if it is set during runtime.
The variables can be retrieved on the Tomcat side as request attributes via request.getAttribute(attributeName). Note that the variables send via JkEnvVar will not be listed in request.getAttributeNames().
The variables are inherited from the global server to virtual hosts.

    JkEnvVar     SSL_CLIENT_V_START     undefined

#### Assigning URLs to Tomcat

If you have created a custom or local version of mod_jk.conf-local as noted above, you can change settings such as the workers or URL prefix.

JkMount directive assign specific URLs to Tomcat. In general the structure of a JkMount directive is:

    JkMount [URL prefix] [Worker name]

    # send all requests ending in .jsp to worker1
    JkMount /*.jsp worker1
    # send all requests ending /servlet to worker1
    JkMount /*/servlet/ worker1
    # send all requests jsp requests to files located in /otherworker will go worker2
    JkMount /otherworker/*.jsp worker2

You can use the JkMount directive at the top level or inside <VirtualHost> sections of your httpd.conf file.

JkUnMount directive acts as an opposite to JkMount and blocks access to a particular URL. The purpose is to be able to filter out the particular content types from mounted context. The following example mounts /servlet/* context, but all .gif files that belongs to that context are not served.

    # send all requests ending with /servlet to worker1
    JkMount /servlet/* worker1
    # do not send requests ending with .gif to worker1
    JkUnMount /servlet/*.gif worker1

JkUnMount takes precedence over JkMount directives, meaning that the JK will first try to mount and then checks, if there is an exclusion defined by a JkUnMount. A JkUnMount overrides a JkMount only, if the worker names in the JkMount and in the JkUnMount are the same.

The following example will block all .gif files although there is a JkMount for them:

    # do not send requests ending with .gif to worker1
    JkUnMount /*.gif worker1
    # The .gif files will not be mounted cause JkUnMount takes
    # precedence over JkMount directive
    JkMount /servlet/*.gif worker1

Starting with version 1.2.26 of JK you can apply a JkUnMount to any worker, by using the star character '*' as the worker name in the JkUnMount. More complex patterns in JkUnMount worker names are not allowed.

    # Mapping the webapps myapp1 and myapp2:
    /myapp1/*=worker1
    /myapp2/*=worker2
    # Exclude the all subdirectories static for all workers:
    !/*/static/*=*
    # Exclude some suffixes for all workers:
    !*.html=*

JkAutoAlias directive automatically Alias webapp context directories into the Apache document space. It enables Apache to serve a static context while Tomcat serving dynamic context. This directive is used for convenience so that you don't have to put an Apache Alias directive for each application directory inside Tomcat's webapp directory. For security reasons it is strongly recommended that JkMount is used to pass all requests to Tomcat by default and JkUnMount is used to explicitly exclude static content to be served by Apache. It should also be noted that content served by Apache will bypass any security constraints defined in the application's web.xml. The directive only works in the simple case of contexts with a single path element and no version marker. It does not support:

- the ROOT context (i.e. .../webapps/ROOT)
- multi-level contexts (e.g. .../webapps/foo#bar)
- parallel deployment (e.g. .../webapps/foo##v00.05.12)

    # enter the full path to the tomcat webapps directory
    JkAutoAlias /opt/tomcat/webapps

The following example shows how to serve a dynamic context by Tomcat and static using Apache. The webapps directory has to be accessible by Apache.

    # enter the full path to the tomcat webapps directory
    JkAutoAlias /opt/tomcat/webapps

    # Mount 'examples' directory. It's physical location
    # is assumed to be in the /opt/tomcat/webapps/examples
    # ajp13w is a worker defined in the workers.properties
    JkMount /examples/* ajp13w

    # Unmount desired static content from examples webapp.
    # This content will be served by the Apache directly.
    JkUnMount /*.gif ajp13w

Note that you can have a single JkAutoAlias directive per virtual host inside your httpd.conf

JkWorkerProperty is a new directive available from JK 1.2.7 version. It is a convenient method for setting directives that are usually set inside workers.propeties file. The parameter for that directive is raw line from workers.properties file.

    # Just like workers.properties but exact line is prefixed
    # with JkWorkerProperty

    # Minimal jk configuration
    JkWorkerProperty worker.list=ajp13w
    JkWorkerProperty worker.ajp13w.type=ajp13
    JkWorkerProperty worker.ajp13w.host=localhost
    JkWorkerProperty worker.ajp13w.port=8009

JkMountFile is a new directive available from JK 1.2.9 version. It is used for dynamic updates of mount points at runtime. When the mount file is changed, JK will reload it's content.

    # Load mount points

    JkMountFile conf/uriworkermap.properties

If the mount point uri starts with an exclamation mark '!' it defines an exclusion in the same way JkUnMount does. If the mount point uri starts with minus sign '-' the mount point will only be disabled. A disabled mount can be reenabled by deleting the minus sign and waiting for the JkMountFile to reload. An exclusion can be disabled by prefixing it with a minus sign.

    # Sample uriworkermap.properties file

    /examples/*=ajp13w
    # Do not map .gif files
    !/*.gif=ajp13w
    # Make jsp examples initially disabled
    -/examples/jsp/*=ajp13w

At run time you can change the content of this file. For example removing minus signs will enable the previously disabled uri mappings. You can add any number of new entries at runtime that reflects the newly deployed applications. Apache will reload the file and update the mount points within 60 second interval.

There is no way to delete entries by dynamic reloading, but you can disable or exclude mappings.

#### Using SetHandler and Environment Variables

Alternatively to the mod_jk specific directives, you can also use SetHandler and environment variables to control, which requests are being forwarded via which worker. This gives you more flexibility, but the results might be more difficult to understand. If you mix both ways of defining the forwards, in general to mod_jk directives will win.

SetHandler jakarta-servlet forces requests to be handled by mod_jk. You can use SetHandler for example in Location blocks or with Apache 2.2 and later also in RewriteRule.

In order to control the worker using SetEnvIf or RewriteRule for more complex rules, you can set the environment variable JK_WORKER_NAME to the name of your chosen target worker. This enables you to decide on the chosen worker in a more flexible way, including dependencies on cookie values. This feature has been added in version 1.2.19 of mod_jk. Furthermore you might append rule extensions to the worker name. The extensions are separated from the worker name by a semicolon ";" using the same syntax as in the uriworkermap.properties file. Supporting rule extensions in the worker name has been added in version 1.2.33.

In order to use another variable than JK_WORKER_NAME, you can set the name of this variable via the JkWorkerIndicator directive.

You can also define exclusions from mod_jk forwards by setting the environment variable no-jk.

    # Automatically map all encoded urls
    <Location *;jsessionid=>
      SetHandler jakarta-servlet
      SetEnv JK_WORKER_NAME my_worker
    </Location>

    # Map all subdirs to workers via naming rule
    # and exclude static content.
    <Location /apps/>
      SetHandler jakarta-servlet
      SetEnvIf REQUEST_URI ^/apps/([^/]*)/ JK_WORKER_NAME=$1
      SetEnvIf REQUEST_URI ^/apps/([^/]*)/static no-jk
    </Location>

#### Advanced Environment Variables

Environment variables allow to overwrite the default behaviour of mod_jk depending on request properties like e.g. the request URI, header values or cookie. This can be done using the SetEnvIf or RewriteRule directives.

The environment variable JK_ROUTE can be set to explicitely choose a member of a load balancer worker. The value must be equal to the route attribute of the member, or if that attribute is not used, equal to the member name. Note that this is only needed if session IDs and routes are encoded in a non standard way in the request. Stickyness using the Java Servlet compliant way of encoding the IDs is supported by default. This is available since version 1.2.33.

The environment variable JK_REPLY_TIMEOUT can be set to dynamically define a reply timeout. The value must be given in milliseconds. This is available since version 1.2.27.

The environment variable JK_STICKY_IGNORE can be set to disable session stickyness for individual requests. If the variable is set to an empty string or a nonzero number, session stickyness will be disabled. Setting it to 0 will reset to the behaviour defined by the worker configuration. This is available since version 1.2.33.

This feature can be useful to optimize load balancing when using cookie based session stickyness. In this case, as long as she keeps her browser open, any request by a user who started a session will be send to the same Tomcat instance, even if he left the part of the application which uses the session. You can for instance set this environment variable when a user requests a login form to ensure, that this initial session request is balanced non-sticky.

The environment variable JK_STATELESS can be used to improve load balancing for the session based balancing methods Session and Next. In this case normally any request which does not come with a session id counts as a new session. This can be problematic, if for instance static content is retrieved without a session id. If you set the environment variable JK_STATELESS for a request, then the request will not count as a new session, even if it does not come with a session id. This is available since version 1.2.33.

The environment variable JK_IGNORE_CL can be set to force ignoring the request Content-Length header (if it exists). mod_jk will then stream the request body until the web server indicates that the full body was read. No Content-Length header will be send to the backend. This is available since version 1.2.41.

This feature can be used to make mod_jk compatible with filters which change the size of the request body. One such filter is mod_deflate when used to inflate the body of a request with gzip encoded body. In this case mod_jk will by default forward a truncated body, because it gets the wrong body size from the web server. Telling mod_jk to ignore the Content-Length header will result in streaming all request body data it can read from the web server to the backend.

You should only set the JK_IGNORE_CL environment variables for requests that actually need it. Unfortunately there's no way for mod_jk to detect the need automatically.