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To run a group of servers as a managed domain you need to configure both the domain controller and each host that joins the domain. This sections focuses on the network configuration for the domain and host controller components. For background information users are encouraged to review the Operating modes and Configuration Files sections.

Domain Controller Configuration

The domain controller is the central government for a managed domain. A domain controller configuration requires two steps:

  • A host needs to be configured to act as the Domain Controller for the whole domain
  • The host must expose an addressable management interface binding for the managed hosts to communicate with it
Example IP Addresses
In this example the domain controller uses 192.168.0.101 and the host controller 192.168.0.10

Configuring a host to act as the Domain Controller is done through the domain-controller declaration in host.xml. If it includes the <local/> element, then this host will become the domain controller:

(See domain/configuration/host.xml)

A host acting as the Domain Controller must expose a management interface on an address accessible to the other hosts in the domain. Exposing an HTTP(S) management interface is not required, but is recommended as it allows the Administration Console to work:

The interface attributes above refer to a named interface declaration later in the host.xml file. This interface declaration will be used to resolve a corresponding network interface. 

(See domain/configuration/host.xml)

Please consult the chapter "Interface Configuration" for a more detailed explanation on how to configure network interfaces.

Next by default the master domain controller is configured to require authentication so a user needs to be added that can be used by the slave domain controller to connect.

Make use of the add-user utility to add a new user, for this example I am adding a new user called slave.

add-user MUST be run on the master domain controller and NOT the slave.

When you reach the final question of the interactive flow answer y or yes to indicate that the new user will be used for a process e.g.

Make a note of the XML Element output as that is going to be required within the slave configuration.

Host Controller Configuration

Once the domain controller is configured correctly you can proceed with any host that should join the domain. The host controller configuration requires three steps:

  • The logical host name (within the domain) needs to be distinct
  • The host controller needs to know the domain controller IP address

Provide a distinct, logical name for the host. In the following example we simply name it "slave":

(See domain/configuration/host.xml)

If the name attribute is not set, the default name for the host will be the value of the jboss.host.name system property. If that is not set, the value of the HOSTNAME or COMPUTERNAME environment variable will be used, one of which will be set on most operating systems. If neither is set the name will be the value of InetAddress.getLocalHost().getHostName().

A security realm needs to be defined to hold the identity of the slave. Since it is performing a specific purpose I would suggest a new realm is defined although it is possible to combine this with an existing realm.

The <secret /> element here is the one output from add-user previously. To create the <secret /> element yourself the value needs to be the password encoded using Base64.

Tell it how to find the domain controller so it can register itself with the domain:

Since we have also exposed the HTTP management interface we could also use :

(See domain/configuration/host.xml)

The username attribute here is optional, if it is omitted then the name of the host will be used instead, in this example that was already set to name.

The name of each host needs to be unique when registering with the domain controller, however the username does not - using the username attribute allows the same account to be used by multiple hosts if this makes sense in your environment.

The <remote /> element is also associated with the security realm SlaveRealm, this is how it picks up the password from the <secret /> element.

Ignoring domain wide resources

WildFly 10 and later make it easy for slave host controllers to "ignore" parts of the domain wide configuration. What does the mean and why is it useful?

One of the responsibilities of the Domain Controller is ensuring that all running Host Controllers have a consistent local copy of the domain wide configuration (i.e. those resources whose address does not begin with /host=*, i.e. those that are persisted in domain.xml. Having that local copy allows a user to do the following things:

  • Ask the slave to launch its already configured servers, even if the Domain Controller is not running.
  • Configured new servers, using different server groups from those current running, and ask the slave to launch them, even if the Domain Controller is not running.
  • Reconfigure the slave to act as the Domain Controller, allowing it to take over as the master if the previous master has failed or been shut down.

However, of these three things only the latter two require that the slave maintain a complete copy of the domain wide configuration. The first only requires the slave to have the portion of the domain wide configuration that is relevant to its current servers. And the first use case is the most common one. A slave that is only meant to support the first use case can safely "ignore" portions of the domain wide configuration. And there are benefits to ignoring some resources:

  • If a server group is ignored, and the deployments mapped to that server group aren't mapped to other non-ignored groups, then the slave does not need to pull down a copy of the deployment content from the master. That can save disk space on the slave, improve the speed of starting new hosts and reduce network traffic.
  • WildFly supports "mixed domains" where a later version Domain Controller can manage slaves running previous versions. But those "legacy" slaves cannot understand configuration resources, attributes and operations introduced in newer versions. So any attempt to use newer things in the domain wide configuration will fail unless the legacy slaves are ignoring the relevant resources. But ignoring resources will allow the legacy slaves to work fine managing servers using profiles without new concepts, while other hosts can run servers with profiles that take advantage of the latest features.

Prior to WildFly 10, a slave could be configured to ignore some resources, but the mechanism was not particularly user friendly:

  • The resources to be ignored had to be listed in a fair amount of detail in each host's configuration.
  • If a new resource is added and needs to be ignored, then each host that needs to ignore that must be updated to record that.

Starting with WildFly 10, this kind of detailed configuration is no longer required. Instead, with the standard versions of host.xml, the slave will behave as follows:

  • If the slave was started with the --backup command line parameter, the behavior will be the same as releases prior to 10; i.e. only resources specifically configured to be ignored will be ignored.
  • Otherwise, the slave will "ignore unused resources".

What does "ignoring unused resources" mean?

  • Any server-group that is not referenced by one of the host's server-config resources is ignored.
  • Any profile that is not referenced by a non-ignored server-group, either directly or indirectly via the profile resource's 'include' attribute, is ignored
  • Any socket-binding-group that is not directly referenced by one of the host's server-config resources, or referenced by a non-ignored server-group, is ignored
  • Extension resources will not be automatically ignored, even if no non-ignored profile uses the extension. Ignoring an extension requires explicit configuration. Perhaps in a future release extensions will be explicitly ignored.
  • If a change is made to the slave host's configuration or to the domain wide configuration that reduces the set of ignored resources, then as part of handling that change the slave will contact the master to pull down the missing pieces of configuration and will integrate those pieces in its local copy of the management model. Examples of such changes include adding a new server-config that references a previously ignored server-group or socket-binding-group, changing the server-group or socket-binding-group assigned to a server-config, changing the profile or socket-binding-group assigned to a non-ignored server-group, or adding a profile or socket-binding-group to the set of those included directly or indirectly by a non-ignored profile or socket-binding-group.

The default behavior can be changed, either to always ignore unused resources, even if --backup is used, or to not ignore unused resources, by updating the domain-controller element in the host-xml file and setting the ignore-unused-configuration attribute:

The "ignore unused resources" behavior can be used in combination with the pre-WildFly 10 detailed specification of what to ignore. If that is done both the unused resources and the explicitly declared resources will be ignored. Here's an example of such a configuration, one where the slave cannot use the "org.example.foo" extension that has been installed on the Domain Controller and on some slaves, but not this one:

Server groups

The domain controller defines one or more server groups and associates each of these with a profile and a socket binding group, and also :

(See domain/configuration/domain.xml)

The domain controller also defines the socket binding groups and the profiles. The socket binding groups define the default socket bindings that are used:

(See domain/configuration/domain.xml)
In this example the bigger-sockets group includes all the socket bindings defined in the standard-sockets groups and then defines an extra socket binding of its own.

A profile is a collection of subsystems, and these subsystems are what implement the functionality people expect of an application server.

(See domain/configuration/domain.xml)
Here we have two profiles. The bigger profile contains all the same subsystems as the default profile (athough the parameters for the various subsystems could be different in each profile), and adds the fictional-example subsystem which references the unique-to-bigger socket binding.

Servers

The host controller defines one or more servers:

(See domain/configuration/host.xml)

server-one and server-two both are associated with main-server-group so that means they both run the subsystems defined by the default profile, and have the socket bindings defined by the standard-sockets socket binding group. Since all the servers defined by a host will be run on the same physical host we would get port conflicts unless we used <socket-binding-group ref="standard-sockets" port-offset="150"/> for server-two. This means that server-two will use the socket bindings defined by standard-sockets but it will add 150 to each port number defined, so the value used for http will be 8230 for server-two.

server-three will not be started due to its auto-start="false". The default value if no auto-start is given is true so both server-one and server-two will be started when the host controller is started. server-three belongs to other-server-group, so if its auto-start were changed to true it would start up using the subsystems from the bigger profile, and it would use the bigger-sockets socket binding group.

JVM

The host controller contains the main jvm definitions with arguments:

(See domain/configuration/host.xml)
From the preceeding examples we can see that we also had a jvm reference at server group level in the domain controller. The jvm's name must match one of the definitions in the host controller. The values supplied at domain controller and host controller level are combined, with the host controller taking precedence if the same parameter is given in both places.

Finally, as seen, we can also override the jvm at server level. Again, the jvm's name must match one of the definitions in the host controller. The values are combined with the ones coming in from domain controller and host controller level, this time the server definition takes precedence if the same parameter is given in all places.

Following these rules the jvm parameters to start each server would be

Server JVM parameters
server-one -Xms64m -Xmx128m
server-two -Xms64m -Xmx256m
server-three -Xms64m -Xmx128m
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  1. Apr 17, 2016

    It would be really nice if there was somewhere that explained, in detail, each of the elements of the  <server> resource - specifically, the jvm resource and the various values you can set for debugging. For instance, the host.xml file that ships with Wildfly shows that you should update the file with the following to enable debugging of the server:

    jvm options

    However, when reviewing the results of reading that resource, it appears there are values that could be set that would be better placed for enabling debugging (e.g. agent-lib, debug-enabled, debug-options, etc). I can guess what they should be, but it would serve myself and others well if it were documented here.

    full jvm resource