How to configure Workers ?

A worker represents a running instance of Tomcat, a worker serves the requests for all dynamic web components.

Each worker is identified by a unique hostname or a unique IP address and port number.

Reasons to implement multiple workers :

• When you want different Web application contexts to be served by different Tomcat workers.
• When you want different virtual hosts to be served by different Tomcat workers.
• When you want to service more requests than the capacity of a single physical server.

A file called workers.properties is created to detail information like, where the Tomcat servers are.

Properties in workers.properties

Worker List properties

worker.list - Describe the workers that are available to Apache via a list

Other Worker Properties

worker.test1.type - Describes the type of worker

worker.test1.host - The host where the worker Tomcat instance resides

worker.test1.port - The port the AJP 1.3 Connector Tomcat instance is listening on (default 8009)

worker.test1.connection_pool_size - The number of connections used for this worker to be kept in a connection pool

worker.test1.connection_pool_minsize - The minimum number of connections kept in a connection pool

worker.test1.connection_pool_timeout - The number of seconds that connections to this worker should be left in the connection before expiry

worker.test1.mount - The contexts paths that are serviced by the worker, you can also use the JkMount directive in the http.conf file

worker.test1.retries - controls the number of times mod_jk will retry when a worker returns a error

worker.test1.socket_timeout - controls how long a worker will wait for a response on a socket before indicating an error

worker.test1.socket_keepalive -  indicates if the connection to the worker should be subject to keep alive

worker.test1.lbfactor - An integer indicating the local-balance factor used by the load balancer to distribute work between multiple instances of Tomcat

Worker Load balancing properties

worker.bal1.balance_workers - A list of workers to load balance between

worker.bal1.lock - The type of locking used O (Optimistic) or P (Pessimistic)

worker.bal1.method - can be set to R (Requests), T (Traffic), B (Busy-ness)

   R = The worker to use is based on the number of requests forwarded

   T = The worker to use is based on the traffic that had been sent to the workers

   B = The worker to use is based on the load dividing the number of concurrent requests by the load factor

worker.bal1.secret - Sets a default secret password for all workers

worker.bal1.sticky_session - Tells the mod_jk to respect the sessionID in the request and ensures that the same session is always serviced by the same worker instance.

worker.bal1.sticky_session_force - This is used for failover

Worker Types

ajp13 : This type of worker represents a running Tomcat instance

lb : used for load balancing

status : display useful information about how the load among the various Tomcat workers is distributed

jni : used in process, this worker handles the forwarding of requests to in-process Tomcat workers using JNDI

ajp12 : worker that support the AJP 1.2 protocol

Example

worker.list = worker1

worker.worker1.type = ajp13

worker.worker1.host = 192.168.0.1

worker.worker1.port = 9009

worker.worker1.connection_pool_size = 5

worker.worker1.connection_pool_timeout = 300

Example (for Load balancing)

worker.list = loadbal1,stat1

worker.tomcatA.type = ajp13

worker.tomcatA.host =192.168.0.1

worker.tomcatA.port = 8009

worker.tomcatA.lbfactor = 10

worker.tomcatB.type = ajp13

worker.tomcatB.host =192.168.0.2

worker.tomcatB.port = 8009

worker.tomcatB.lbfactor = 10

worker.tomcatC.type = ajp13

worker.tomcatC.host =192.168.0.3

worker.tomcatC.port = 8009

worker.tomcatC.lbfactor = 10

worker.loadbal1.type = lb

worker.loadbal1.sticky_seesion = 1

worker.loadbal1.balance_workers = tomcatA, tomcatB, tomcatC

worker.stat1.type= status