# Tomcat Connector

## workers.properties configuration

Introduction

> A Tomcat worker is a Tomcat instance that is waiting to execute servlets or any other content on behalf of some web server. For example, we can have a web server such as Apache forwarding servlet requests to a Tomcat process (the worker) running behind it.

> The scenario described above is a very simple one; in fact one can configure multiple Tomcat workers to serve servlets on behalf of a certain web server. The reasons for such configuration can be:

> - We want different contexts to be served by different Tomcat workers to provide a development environment where all the developers share the same web server but own a Tomcat worker of their own.
> - We want different virtual hosts served by different Tomcat processes to provide a clear separation between sites belonging to different companies.
> - We want to provide load balancing, meaning run multiple Tomcat workers each on a machine of its own and distribute the requests between them.

> There are probably more reasons for having multiple workers but I guess that this list is enough... Tomcat workers are defined in a properties file dubbed workers.properties and this tutorial explains how to work with it.

Directives

> Each workers.properties directive consists of three words separated by dot. The first word is always worker. The second word is the worker name that can be any name. The worker name reflects the name of the jvmRoute defined in Tomcat's server.xml configuration file.

> The name of the worker can contain only the alphanumeric characters [a-z][A-Z][0-9] and is case sensitive.

> Defining workers

> > The generic workers.properties directive is in the form:

> > worker.<worker name>.<directive>=<value>

> > Defining workers to the Tomcat web server plugin can be done using a properties file (a sample file named workers.properties is available in the conf/ directory).

> > Directive | Default | Description
> > --- | --- | ---
> > `worker.list` | `ajp13` | A comma separated list of workers names that the JK will use. When starting up, the web server plugin will instantiate the workers whose name appears in the worker.list property, these are also the workers to whom you can map requests.

> > `worker.maintain`

> > `60`

> > Worker connection pool maintain interval in seconds. If set to the positive value JK will scan all connections for all workers specified in worker.list directive and check if connections needs to be recycled.

> > Furthermore any load balancer does a global maintenance every worker.maintain seconds. During global maintenance load counters are decayed and workers in error are checked for recover_time.

> > This feature has been added in jk 1.2.13.

> Mandatory directives

> > Mandatory directives are the one that each worker must contain. Without them the worker will be unavailable or will misbehave.

> > Directive | Default | Description
> > --- | --- | ---

> > `type`

> > `ajp13`

> > Type of the worker (can be one of ajp13, ajp14, jni, lb or status). The type of the worker defines the directives that can be applied to the worker.

> > AJP13 worker is the preferred worker type that JK uses for communication between web server and Tomcat. This type of worker uses sockets as communication channel. For detailed description of the AJP13 protocol stack browse to AJPv13 protocol specification

> Connection directives

> > Connection directives defines the parameters needed to connect and maintain the connections pool of persistent connections between JK and remote Tomcat.

> > Directive | Default | Description
> > --- | --- | ---
> > `host` | `localhost` | Host name or IP address of the backend Tomcat instance. The remote Tomcat must support the ajp13 protocol stack. The host name can have a port number embedded separated by the colon (':') character.
> > `port` | `8009` | Port number of the remote Tomcat instance listening for defined protocol requests. The default value depends on the worker type. For AJP13 workers the default port is 8009, while for AJP14 type of worker that value is 8011.
> > `socket_timeout` | `0` | Socket timeout in seconds used for communication channel between JK and remote host. If remote host does not respond inside that timeout the JK will generate an error, and retry again. If set to value zero (default) the JK will wait for infinite on all socket operations.

> > `socket_keepalive`

> > `False`

> > This directive should be used when you have a firewall between your webserver and the Tomcat engine, who tend to drop inactive connections. This flag will told Operating System to send KEEP_ALIVE message on inactive connections (interval depend on global OS settings, generally 120 minutes), and thus prevent the firewall to cut the connection. To enable keepalive set this property value to the True.

> > The problem with Firewall cutting inactive connections is that sometimes, neither webserver or tomcat have information about the cut and couldn't handle it.

> > `retries` | `3` | The number of retries that the worker will try in case of error returned from remote Tomcat. If the number of retries set is greater then three (the default value), on each retry after default an extra wait of 100ms will be inserted.

> > `connection_pool_size`

> > `1`

> > This defines the number of connections made to the AJP backend that are maintained as a connection pool. It will limit the number of those connection that each web server child process can made.

> > Connection pool size property is used only for multi threaded web servers such as Apache 2.0 (worker), IIS and Netscape. The connection_pool_size property should reflect the number of threads per child process. JK will discover the number of threads per child process on Apache 2 web server with worker-mpm and set its default value to match the ThreadsPerChild Apache directive. For IIS the default value is 10. For other web servers this value has to be set manually.

> > Do not use connection_pool_size with values higher then 1 on Apache 2.x prefork or Apache 1.3.x!

> > `connection_pool_minsize` | `pool/2` | Minimum size of the connection pool that will be maintained. This property is used only when the connection_pool_size is specified. Its default value is connection_pool_size/2. Do not use connection_pool_size with values higher then 1 on Apache 2.x prefork or Apache 1.3.x! This feature has been added in jk 1.2.16.

> > `connection_pool_timeout`

> > `0`

> > Cache timeout property should be used with connection_pool_size to specify how long JK should keep an inactive socket in cache before closing it. This property should be used to reduce the number of threads on the Tomcat WebServer.

> > Each child could open an ajp13 connection if it have to forward a request to Tomcat, creating a new ajp13 thread on Tomcat side.

> > The problem is that after an ajp13 connection is created, the child won't drop it until killed. And since the webserver will keep its childs/threads running to handle high-load, even it the child/thread handle only static contents, you could finish having many unused ajp13 threads on the Tomcat side.

> > .

> > `lbfactor`

> > `1`

> > Integer number used when the worker will be used inside load balancer worker, this is the load-balancing factor for the worker. The load-balancing factor is how much we expect this worker to work, or the worker's work quota. Load balancing factor is compared with other workers that makes the load balancer. For example if one worker has lb_factor 5 times higher then other worker, then it will receive five times more requests.

> > Some directives have been deprecated in the past. We include their documentation in case you need to use an older version of mod_jk. We urge you to update and not use them any more. Please migrate your existing configurations.

> > Directive | Default | Description
> > --- | --- | ---

> > `recycle_timeout`

> > `0`

> > This directive has been deprecated since 1.2.16. See connection_pool_timeout instead.

> > The number of seconds that told webserver to cut an ajp13 connection after some time of inactivity. When choosing an endpoint for a request and the assigned socket is open, it will be closed if it was not used for the configured time. It's a good way to ensure that there won't too old threads living on Tomcat side, with the extra cost you need to reopen the socket next time a request be forwarded. This property is very similar to cache_timeout but works also in non-cache mode. If set to value zero (default) no recycle will took place.

> > `cache_timeout`

> > `0`

> > This directive has been deprecated since 1.2.16. See connection_pool_timeout instead.

> > Cache timeout property should be used with cachesize to specify how to time JK should keep an open socket in cache before closing it. This property should be used to reduce the number of threads on the Tomcat WebServer.

> > Each child could open an ajp13 connection if it have to forward a request to Tomcat, creating a new ajp13 thread on Tomcat side.

> > The problem is that after an ajp13 connection is created, the child won't drop it until killed. And since the webserver will keep its childs/threads running to handle high-load, even it the child/thread handle only static contents, you could finish having many unused ajp13 threads on the Tomcat side.

> > .

> > `cachesize`

> > `1`

> > This directive has been deprecated since 1.2.16. See connection_pool_size instead.

> > Cachesize defines the number of connections made to the AJP backend that are maintained as a connection pool. It will limit the number of those connection that each web server child process can made.

> > Cachesize property is used only for multi threaded web servers such as Apache 2.0 (worker), IIS and Netscape. The cachesize property should reflect the number of threads per child process. JK will discover the number of threads per child process on Apache 2 web server with worker-mpm and set its default value to match the ThreadsPerChild Apache directive. For IIS the default value is 10. For other web servers this value has to be set manually.

> > Do not use cachesize with values higher then 1 on Apache 2.x prefork or Apache 1.3.x!

> Load balancing directives

> > Load balancer is a virtual worker that does not really communicate with Tomcat workers. Instead it is responsible for the management of several "real" workers. The worker is supposed to be a load balancer if it's worker type is lb. See worker's type directive. The workers that are member of load balancer must not appear in the worker.list directive.

> > Loadbalancer directives defines the parameters needed to create a workers that are connecting to a remote cluster of backend Tomcat servers. Each cluster node has to have a worker defined.

> > Load balancer management includes:

> > - Instantiating the workers in the web server.
> > - Using the worker's load-balancing factor, perform weighed-round-robin load balancing where high lbfactor means stronger machine (that is going to handle more requests)
> > - Keeping requests belonging to the same session executing on the same Tomcat worker.
> > - Identifying failed Tomcat workers, suspending requests to them and instead fall-backing on other workers managed by the lb worker.

> > The overall result is that workers managed by the same lb worker are load-balanced (based on their lbfactor and current user session) and also fall-backed so a single Tomcat process death will not "kill" the entire site. The following table specifies properties that the lb worker can accept:

> > Directive | Default | Description
> > --- | --- | ---
> > `balance_workers` | `-` | A comma separated list of workers that the load balancer need to manage. This directive replaces old balanced_workers directive and can be used only with mod_jk versions 1.2.7 and up. These workers should not appear in the worker.list property!
> > `sticky_session` | `True` | Specifies whether requests with SESSION ID's should be routed back to the same Tomcat worker. If sticky_session is set to True or 1 sessions are sticky, otherwise sticky_session is set to False. Set sticky_session to False when Tomcat is using a Session Manager which can persist session data across multiple instances of Tomcat. By default sticky_session is set to True.

> > `sticky_session_force`

> > `False`

> > Specifies whether requests with SESSION ID's for workers that are in error state should be rejected. If sticky_session_force is set to True or 1 and the worker that matches that SESSION ID is in error state, client will recieve 500 (Server Error). If set to False or 0 failover on another worker will be issued with loosing client session. This directive is used only when you set sticky_session=True.

> > This feature has been added in jk 1.2.9.

> > `method`

> > `Request`

> > Specifies what method load balancer is using for electing best worker. If method is set to R[equest] balancer will use number of requests to find the best worker. If set to T[raffic] balancer will use the network traffic between JK and Tomcat to find the best worker. If set to B[usyness] balancer will pick the worker with the lowest current load, based on how many requests the worker is currently serving. This number is divided by the workers lbfactor, and the lowest value (least busy) worker is picked.

> > This feature has been added in jk 1.2.9.

> > `lock`

> > `Optimistic`

> > Specifies what lock method the load balancer will use for synchronizing shared memory runtime data. If lock is set to O[ptimistic] balancer will not use shared memory lock to find the best worker. If set to P[essimistic] balancer will use shared memory lock. The balancer will work more accurately in case of Pessimistic locking, but can slow down the average response time.

> > This feature has been added in jk 1.2.13.

> > `secret` | `-` | Set a default secret word for all defined workers. See worker secret attribute description for more info. This feature has been added in jk 1.2.12.

> Status Worker directives

> > The status worker does not communicate with Tomcat. Instead it is responsible for the load balancer management.

> > Directive | Default | Description
> > --- | --- | ---
> > `css` | `-` | Specifies the url for cascading stylesheet to use.

> Advanced worker directives

> > Directive | Default | Description
> > --- | --- | ---

> > `connect_timeout`

> > `0`

> > Connect timeout property told webserver to send a PING request on ajp13 connection after connection is established. The parameter is the delay in milliseconds to wait for the PONG reply.

> > This features has been added in jk 1.2.6 to avoid problem with hung tomcat's and require ajp13 ping/pong support which has been implemented on Tomcat 3.3.2+, 4.1.28+ and 5.0.13+. Disabled by default.

> > `prepost_timeout`

> > `0`

> > Prepost timeout property told webserver to send a PING request on ajp13 connection before forwarding to it a request. The parameter is the delay in milliseconds to wait for the PONG reply.

> > This features has been added in jk 1.2.6 to avoid problem with hung tomcat's and require ajp13 ping/pong support which has been implemented on Tomcat 3.3.2+, 4.1.28+ and 5.0.13+. Disabled by default.

> > `reply_timeout`

> > `0`

> > Reply_timeout property told webserver to wait some time for reply to a forwarded request before considering the remote tomcat is dead and eventually switch to another tomcat in a cluster group. By default webserver will wait forever which could be an issue for you. The parameter is the number of milliseconds to wait for reply, so adjust it carefully if you have long running servlets.

> > This features has been added in jk 1.2.6 to avoid problem with hung tomcat's and works on all servlet engines supporting ajp13. Disabled by default.

> > `recover_time`

> > `60`

> > The recover time is the time in seconds the load balancer will not try to use a worker, after it went into error state. Only after this time has passed, a worker in error state will be marked as in recovering, so that it will be tried for new requests.

> > This interval is not checked every time a request is being processed. Instead it is being checked during global maintenance. The time between two runs of global maintenance is controlled by worker.maintain.

> > Do not set recover_time to a very short time unless you understand the implications. Every recovery attempt for a worker in error is done by a real request!

> > `recovery_options`

> > `0`

> > Recovery options property told webserver how to handle recovery when it detect that tomcat failed. By default, webserver will forward the request to another tomcat in LB mode (or to another ajp thread in ajp13 mode). values are : 0 (full recovery), 1 (don't recover if tomcat failed after getting the request), 2 (don't recover if tomcat failed after sending the headers to client), 3 (don't recover if tomcat failed getting the request or after sending the headers to client).

> > This features has been added in jk 1.2.6 to avoid problem with hung/broken tomcat's and works on all servlet engines supporting ajp13. Full recovery by default.

> > If the value 4 is added to the recovery options, the connection between the webserver and tomcat will be closed if the client connection to the webserver is terminated during the request/response cycle. This allows to inform the servlet engine about broken client connections during lengthy operations. This feature has been added in jk 1.2.16

> > `distance` | `0` | Express preferences between the balanced workers of an lb worker. A load balancer will never choose some balanced worker in case there is another usable worker with lower distance. Only in case all workers below a given distance are in error, disabled or stopped, workers of a larger distance are eligible for balancing.

> > `domain`

> > `-`

> > Domain directive can be used only when the worker is a member of the load balancer. Workers that share the same domain name are treated as single worker. If sticky_session is used, then the domain name is used as session route.

> > This directive is used for large system with more then 6 Tomcats, to be able to cluster the Tomcats in two groups and thus lowering the session replication transfer between them.

> > This feature has been added in jk 1.2.8.

> > `redirect` | `-` | Set to the preferred failover worker. If worker matching SESSION ID is in error state then the redirect worker will be used instead. It will be used even if being disabled, thus offering hot standby. This feature has been added in jk 1.2.9.

> > `activation`

> > `Active`

> > Using this directive, a balanced worker of a load balancer can be configured as disabled or stopped. A disabled worker only gets requests, which belong to sessions for that worker. A stopped worker does not get any requests. Users will loose their sessions, unless session replication via clustering is used.

> > Use d or D to disable and s or S to stop. If this directive is not present the deprecated directives "disabled" or "stopped" are used.

> > This flag can be changed at runtime using status worker.

> > This feature has been added in jk 1.2.19.

> > `disabled` | `False` | This directive has been deprecated since 1.2.19. See activation instead. If set to True or 1 the worker will be disabled if member of load balancer. This flag can be changed at runtime using status worker. This feature has been added in jk 1.2.9.

> > `stopped`

> > `False`

> > This directive has been deprecated since 1.2.19. See activation instead.

> > If set to True or 1 the worker will be stopped if member of load balancer. The flag is needed for stop complete traffic of a sticky session worker. It is only usefull, when you have a cluster that replicated the sessions. This flag can be changed at runtime using status worker.

> > This feature has been added in jk 1.2.11.

> > `jvm_route`

> > `-`

> > Normally the name of a balanced worker in a load balancer is equal to the jvmRoute of the corresponding Tomcat instance. If you want to include a worker corresponding to a Tomcat instance into several load balancers with different balancing configuration (e.g. disabled, stopped) you can use this attribute.

> > Define a seperate worker per lb and per Tomcat instance with an arbitrary worker name and set the jvm_route attribute of the worker equal to the jvmRoute of the target Tomcat instance.

> > If this attribute is left empty, the name of the worker will be used.

> > This feature has been added in jk 1.2.16.

> > `reference`

> > `-`

> > This directive allows to copy configurations between workers in a hierarchical way. If worker castor sets worker.castor.reference=worker.pollux then it inherits all properties of pollux, except for the ones that are explicitely set for castor.

> > Please note, that the value of the directive is not only the name of the referred worker, but the complete prefix including "worker.".

> > This directive is especially useful, if one has a lot of balanced workers in a load balancer and these workers share most of their properties. You can set all of these properties in a phantom worker, e.g. using the prefix "worker.template1", and then simply reference those common properties in all balanced workers.

> > This feature has been added in jk 1.2.19.

> > `secret` | `-` | If set to AJP Connector secret keyword, only request with this keyword are successfull responding. Use request.useSecret="true" and request.secret="secret key word" at your tomcat ajp Connector configuration.
> > `mount` | `-` | Space delimted list of uri maps the worker should handle

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