Red Hat JBoss Enterprise Application Platform Administration I

In a Red Hat JBoss Enterprise Application Platform (JBoss EAP) managed domain, the host controller is responsible for starting the Java Virtual Machine (JVM) process for each server in the managed domain. The JVM options for each individual server can be configured at three different levels:

A JVM memory option that displays at a lower level, closer to the server level, overrides any inherited option from a higher level. More specifically:

JBoss EAP uses the <jvm> configuration tag for defining different options for JVM processes. You can define <jvm> at all three configuration levels by using the management console or the management CLI.

You can define a <jvm> at the host controller level in the host.xml file, within the <jvms> tag. A sample <jvm> definition in the host.xml looks like the following snippet:

<jvms>
     <jvm name="small_jvm">
         <heap size="64m" max-size="128m"/>
     </jvm>
     <jvm name="production_jvm">
         <heap size="2048m" max-size="2048m"/>
         <jvm-options>
            <option value="-server"/>
         </jvm-options>
     </jvm>
</jvms>

The corresponding CLI command to define the JVMs is as follows:

/host=servera/jvm=small_jvm:add(heap-size=64m,max-heap-size=128m)

/host=servera/jvm=production_jvm:add(
    heap-size=2048m,
    max-heap-size=2048m,
    jvm-options=["-server"]
)

In the preceding definition, the small_jvm JVM has a minimum heap size of 64 MB and a maximum heap size of 128 MB. The production_jvm JVM has minimum and maximum heap size of 2 GB and an option named -server is set for the JVM. You can pass multiple JVM options in this manner.

A server-group definition in the domain.xml file uses the <jvm> tag to specify which <jvm> definition to use. For example, the following server-group definition in domain.xml uses a JVM called production_jvm:

<server-group name="groupA" profile="default">
    <jvm name="production_jvm"/>
    <socket-binding-group ref="standard-sockets"/>
</server-group>

The corresponding CLI command is as follows:

/server-group=groupA:add \
      (profile=default,socket-binding-group=standard-sockets) \
      /server-group=groupA/jvm=production_jvm:add()

Any server in the groupA server group inherits the JVM options from the production_jvm. A server-group can override the settings of the <jvm> definition. For example, the following server-group definition changes the heap size of the production_jvm:

<server-group name="groupB" profile="default">
       <jvm name="production_jvm">
           <heap size="1024m" max-size="1024m"/>
       </jvm>
       <socket-binding-group ref="standard-sockets"/>
</server-group>

Any server in the groupB server group has a minimum and maximum heap size of 1024MB, and its other JVM settings are inherited from the production_jvm definition.

/server-group=groupA/jvm=groupa-jvm:add \
  (heap-size=512m,max-heap-size=512mm,jvm-options=["-server"])

You can configure the JVM options at the server level, within the <server> definition in the host.xml file. A new <jvm> can be defined , and it can also override any JVM settings that the server inherits from either its server group definition, or its jvm definition at the host controller level. A sample definition at the server level is as follows:

<server name="test_server" group="groupB" auto-start="true">
    <socket-binding-group ref="standard-sockets" port-offset="300"/>
  <jvm name="production_jvm">
       <heap size="256m"/>
  </jvm>
</server>

In the previous example, test_server uses the settings from production_jvm, except for the initial heap size, which is 256MB instead of the 1024MB defined in the groupB server group.

/host=host3/server-config=serverX \
  /jvm=serverX-jvm:add \
  (heap-size=512m,max-heap-size=1500m, \
  jvm-options=["-server","-XX:ParallelGCThreads=4"])