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The mod_cluster integration is done via the modcluster subsystem.


Instance ID or JVMRoute

The instance-id or JVMRoute defaults to property passed on server startup (e.g. via

To configure instance-id statically, configure the corresponding property in Undertow subsystem:


By default, mod_cluster is configured for multicast-based discovery. To specify a static list of proxies, create a remote-socket-binding for each proxy and then reference them in the 'proxies' attribute. See the following example for configuration in the domain mode:

Runtime Operations

The modcluster subsystem supports several operations:

The operations specific to the modcluster subsystem are divided in 3 categories the ones that affects the configuration and require a restart of the subsystem, the one that just modify the behaviour temporarily and the ones that display information from the httpd part.

operations displaying httpd informations

There are 2 operations that display how Apache httpd sees the node:


Send a DUMP message to all Apache httpd the node is connected to and display the message received from Apache httpd.


Send a INFO message to all Apache httpd the node is connected to and display the message received from Apache httpd.

operations that handle the proxies the node is connected too

there are 3 operation that could be used to manipulate the list of Apache httpd the node is connected too.


Displays the httpd that are connected to the node. The httpd could be discovered via the Advertise protocol or via the proxy-list attribute.


Remove a proxy from the discovered proxies or  temporarily from the proxy-list attribute.


Add a proxy to the discovered proxies or  temporarily to the proxy-list attribute.

Context related operations

Those operations allow to send context related commands to Apache httpd. They are send automatically when deploying or undeploying  webapps.


Tell Apache httpd that the context is ready receive requests.


Tell Apache httpd that it shouldn't send new session requests to the context of the virtualhost.


Tell Apache httpd that it shouldn't send requests to the context of the virtualhost.

Node related operations

Those operations are like the context operation but they apply to all webapps running on the node and operation that affect the whole node.


Refresh the node by sending a new CONFIG message to Apache httpd.


reset the connection between Apache httpd and the node


Metric configuration

There are 4 metric operations corresponding to add and remove load metrics to the dynamic-load-provider. Note that when nothing is defined a simple-load-provider is use with a fixed load factor of one.

that corresponds to the following configuration:


Add a metric to the dynamic-load-provider, the dynamic-load-provider in configuration is created if needed.


Remove a metric from the dynamic-load-provider.

add-custom-metric / remove-custom-metric

like the add-metric and remove-metric except they require a class parameter instead the type. Usually they needed additional properties which can be specified

which corresponds the following in the xml configuration file:

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