Appendix D. Workers.properties file for mod_jk

If you want to use the mod_jk connector, you must create a JBCS_HOME/httpd/conf/workers.properties file on the Apache HTTP Server host to define the back-end worker nodes. The worker nodes are servlet containers that you can map to the mod_jk load balancer. The workers.properties file specifies the location of the servlet containers and how to load-balance calls across these servlet containers.

This appendix describes the layout and content of the workers.properties file.

Depending on the Apache HTTP Server distribution that you are using, the location of the workers.properties file varies:

  • If you are using the JBCS Apache HTTP Server, the workers.properties file is in the JBCS_HOME/httpd/conf.d directory.

  • If you are using the RHEL Apache HTTP Server, the workers.properties file is in the /etc/httpd/conf.d directory.

    Note

    The RHEL Apache HTTP Server supports the use of mod_jk on RHEL 9 only.

D.1. Workers.properties overview

The workers.properties file contains a global properties section and a worker properties section.

Global Properties
This section contains directives that apply to all workers.
Worker Properties
This section contains directives that apply to each individual worker.

Each node is defined using the worker properties naming convention. The worker name can only contain lowercase letters, uppercase letters, numbers, and specific special characters (_, /).

The structure of a worker property is worker.WORKER_NAME.DIRECTIVE.

worker
The constant prefix for all worker properties.
WORKER_NAME
The arbitrary name given to the worker. For example: node1, node_01, Node_1.
DIRECTIVE
The specific directive required.

D.2. Workers.properties directives

The workers.properties file directives are divided into global, mandatory, connection, and load-balancing classifications.

Global directives for workers.properties

worker.list

Specifies the list of worker names that mod_jk uses. The workers in this list are available to map requests to.

Note

A single node configuration which is not managed by a load balancer must be set to worker.list=WORKER_NAME.

Mandatory directives for workers.properties

type

Specifies the type of worker, which determines the directives applicable to the worker. The default value is ajp13, which is the preferred worker type to select for communication between the web server and Apache HTTP Server.

Other values include lb and status.

For detailed information about AJPv13, see the Apache Tomcat Connector - AJP Protocol Reference.

Connection directives for workers.properties

host

The hostname or IP address of the worker. The worker node must support the ajp13 protocol stack. The default value is localhost.

You can specify the port directive as part of the host directive by appending the port number after the host name or IP address. For example: worker.node1.host=192.168.2.1:8009 or worker.node1.host=node1.example.com:8009.

port
The port number of the remote server instance listening for the defined protocol requests. The default value is 8009, which is the default listen port for AJPv13 workers.
ping_mode

Specifies the conditions under which connections are probed for their current network health.

The probe uses an empty AJPv13 packet for the CPing, and expects a CPong in return, within a specified timeout.

You specify the conditions by using a combination of the directive flags. The flags are not comma-separated. For example, a correct directive flag set is worker.node1.ping_mode=CI.

C (connect)
Specifies the connection is probed once after connecting to the server. You specify the timeout using the connect_timeout directive, otherwise the value for ping_timeout is used.
P (prepost)
Specifies that the connection is probed before sending each request to the server. You specify the timeout using the prepost_timeout directive, otherwise the value for ping_timeout is used.
I (interval)
Specifies that the connection is probed during regular internal maintenance cycles. You specify the idle time between each interval using the connection_ping_interval directive, otherwise the value for ping_timeout is used.
A (all)
The most common setting, which specifies that all directive flags are applied. For information about the \*_timeout advanced directives, see the Apache Tomcat Connector - Reference Guide.
ping_timeout
Specifies the time to wait for CPong answers to a CPing connection probe (see ping_mode). The default value is 10000 (milliseconds).

Load balancing directives for workers.properties

lbfactor

Specifies the load-balancing factor for an individual worker, and is only specified for a member worker of a load balancer.

This directive defines the relative amount of HTTP request load distributed to the worker compared to other workers in the cluster.

A common example where this directive applies is where you want to differentiate servers with greater processing power than others in the cluster. For example, if you require a worker to take three times the load than other workers, specify worker.WORKER_NAME.lbfactor=3.

balance_workers
Specifies the worker nodes that the load balancer must manage. The directive can be used multiple times for the same load balancer, and consists of a comma-separated list of worker names as specified in the workers.properties file.
sticky_session

Specifies whether requests for workers with SESSION IDs are routed back to the same worker. The default is 0 (false). When set to 1 (true), load balancer persistence is enabled.

For example, if you specify worker.loadbalancer.sticky_session=0, each request is load balanced between each node in the cluster. In other words, different requests for the same session can go to different servers based on server load.

If you specify worker.loadbalancer.sticky_session=1, each session is persisted (locked) to one server until the session is terminated, providing that server is available.

Additional resources