[[EJB_on_Kubernetes]]
= EJB on Kubernetes

If the WildFly server is deployed on Kubernetes then there are several
points that you need to bear in mind when you use EJBs.

NOTE: When deploying on Kubernetes you should consider the use of the link:https://github.com/wildfly/wildfly-operator[WildFly Operator].
      It manages the Kubernetes objects in WildFly friendly way.
      For example, it uses StatefulSet for the correct handling of EJB remoting and transaction recovery processing.

The rest of this chapter assumes the link:https://kubernetes.io/docs/concepts/workloads/controllers/statefulset/[`StatefulSet`] is used
as the Kubernetes API object for managing the WildFly server.

The StatefulSet provides a guarantee of persistent storage and network hostname stability
over the restarts of the pod.

These two guarantees are particularly important for the transaction manager which is a stateful component.
The persistent storage over restarts is needed as the transaction log is usually stored at the file system.
If the transaction manager creates a transaction log record it's created only at the transaction log particular to the WildFly instance.
The hostname stability is needed as the WildFly may be contacted via EJB remote call with transaction propagation.
The WildFly has to be reachable under the same hostname even after pod restarts.
As the transaction log is bound to the particular WildFly instance it may be finished only there.


[[ejb-calls-on-kubernetes]]
== EJB calls on Kubernetes

The EJB caller has two options on how to configure the remote call.
It can be defined either as a remote outbound connection (see details at link:Admin_guide{outfilesuffix}#outbound-connections[Admin Guide, section Outbound Connections])
or you may use a direct `InitialContext` lookup in your code.

If you use either case then for the Kubernetes you need to adjust the configuration of the target node.
For the target hostname, you need to use the DNS name of the very first pod managed by `StatefulSet`.

The `StatefulSet` guarantees depend on the ordering of the pods. The pods are named in the prescribed order.
If you scale your application up to 3 replicas you may expect
your pods will have names such as `wildfly-server-0`, `wildfly-server-1`, `wildfly-server-2`.

It's expected a link:https://kubernetes.io/docs/concepts/services-networking/service/#headless-services[headless services]
to be used along with the `StatefulSet`. With the headless service, there is ensured the DNS hostname for the pod.
If the application uses the WildFly Operator, a headless service will be created with a name such as `wildfly-server-headless`.
Then the DNS name of the very first pod will be `wildfly-server-0.wildfly-server-headless`.

The use of the hosname `wildfly-server-0.wildfly-server-headless`
guarantees that the EJB call may reach any WildFly instance connected to the cluster.
It's a bootstrap connection which is used to initialize the EJB client
which gathers the structure of the WildFly cluster as the next step.


[[ejb-kubernetes-configuration]]
== EJB configuration for Kubernetes

These are steps you need to process in order to run EJB remote calls.
Some steps are related to the server configuration, the other ones
on your application.

* The clustering has to be set correctly, see the link:High_Availability_Guide{outfilesuffix}#discovery-for-kubernetes[High Availability Guide, section of Kubernetes discovery].
* All the `socket-binding` must define the client mapping for the DNS value mapped by `StatefulSet` headless service.
  For example if the application is named `wildfly-server` and the `StatefulSet` headless service is named `wildfly-server-headless`
  then the `http` socket binding has to be defined in the following way:

[source,xml,options="nowrap"]
----
<socket-binding name="http" port="${jboss.http.port:8080}">
   <client-mapping destination-address="${jboss.node.name}.wildfly-server-headless"/>
</socket-binding>
----

* A small workaround is needed for the remote EJB transaction recovery on Kubernetes
  (the issue could be tracked at link:https://issues.jboss.org/browse/WFCORE-4668[WFCORE-4668]).
  The WildFly application server has to be configured with property `wildfly.config.url`.
  The `wildfly.config.url` points to a XML configuration file. If we consider one being placed at `$JBOSS_HOME/standalone/configuration/wildfly-config.xml`
  then the property is setup as `JAVA_OPTS="$JAVA_OPTS -Dwildfly.config.url=$JBOSS_HOME/standalone/configuration/wildfly-config.xml"`.
  The `wildfly-config.xml` defines the EJB recovery authentication to be used during transaction recovery for remote EJB calls.
  The target server has to configure a user that is permitted to receive the EJB remote calls.
  Such a user is then configured by standard means of link:Admin_Guide{outfilesuffix}#application-realm[security configuration].
  Let’s say there is configured a user on the target server.
  The user is created with script `$JBOSS_HOME/bin/add-user.sh` under the `ApplicationRealm`.
  Then the caller WildFly uses the configuration in `wildfly-config.xml` this way
  (you may copy the content below, but replace the `>>PASTE_..._HERE<<` with user and password you configured):

[source,xml,options="nowrap"]
----
<configuration>
  <authentication-client xmlns="urn:elytron:1.0">
  <authentication-rules>
          <rule use-configuration="jta">
              <match-abstract-type name="jta" authority="jboss"/>
      </rule>
      </authentication-rules>
      <authentication-configurations>
       <configuration name="jta">
               <sasl-mechanism-selector selector="DIGEST-MD5"/>
               <providers>
                   <use-service-loader />
           </providers>
       <set-user-name name=">>PASTE_USER_NAME_HERE<<"/>
           <credentials>
                    <clear-password password=">>PASTE_PASSWORD_HERE<<"/>
           </credentials>
               <set-mechanism-realm name="ApplicationRealm" />
           </configuration>
      </authentication-configurations>
  </authentication-client>
</configuration>
----
