Let's say something like this is being returned. 

[standalone@embedded /] echo Cannot configure jgroups 'kubernetes.KUBE_PING' protocol under 'tcp' stack. This protocol is already configured. >> ${error_file}

I got this after I made a change to one of the files in the /opt/eap/standalone/configuration directory in a JBOSS pod deployed to OpenShift. For more details on JBOSS on OpenShift, check out my article FreeKB - JBOSS - Getting Started with JBOSS on OpenShift.

Let's start by creating a Persistent Volume Claim. I had to go with a Persistent Volume Claim instead of a Config Map because a Config Map gets mounted in the container read only but a Persistent Volume Claim can be mounted with write access, and the JBOSS container needs to be able to write to files in the /opt/eap/standalone/configuration directory. Check out these articles for my notes on how to create a Persistent Volume and Persistent Volume Claim.

• FreeKB - OpenShift - Create Persistent Volume
• FreeKB - OpenShift - Create Persistent Volume Claim

For example, I created a Persistent Volume Claim named my-persistent-volume-claim that had Access Mode RWX (Read Write Many).

~]$ oc get pvc --output wide
NAME                         STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE      VOLUMEMODE
my-persistent-volume-claim   Bound    pvc-2db07c57-e282-48e7-bfb1-4cbd7245c25e   1Gi        RWX            file-storage   3m29s    Filesystem

You'll want to ensure that the JBOSS deployment/pod is running with a Security Context Constraint that allows Persistent Volumes to be mounted in the container. By default, if a pod is not associated with a specific Service Account that has been bound to a certain Security Context Constraint, the pod should have the restricted Security Context Constraint, which can be seen using the oc describe pod command.

~]$ oc describe pod my-app-kf7hf
Annotations:  openshift.io/scc: restricted

The oc get securitycontextconstraints command can be used to see that the restricted Security Context Constraint has persistentVolumeClaim for VOLUMES. In other words, the pod is running with a Security Context Constraint that allows Persistent Volumes to be mounted in the container. If the pod is running with a Security Context Constraint that does not have persistentVolumeClaim for VOLUMES, check out my article FreeKB - OpenShift - Run a deployment with a Service Account and Security Context Constraint.

~]$ oc get securitycontextconstraints restricted
NAME         PRIV    CAPS         SELINUX     RUNASUSER        FSGROUP     SUPGROUP   PRIORITY     READONLYROOTFS   VOLUMES
restricted   false   <no value>   MustRunAs   MustRunAsRange   MustRunAs   RunAsAny   <no value>   false            ["configMap","downwardAPI","emptyDir","persistentVolumeClaim","projected","secret"]

Then I updated the JBOSS deployment to mount the Persistent Volume Claim to /var/data in the container. Check out my article FreeKB - OpenShift - Mount a Persistent Volume in a container for more details on how to mount a Persistent Volume Claim in a container. Here is a snippet of the deployment YAML with my-persistent-volume-claim mount to the /var/data directory in the JBOSS container.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: eap74-openjdk8-openshift-rhel7
spec:
  template:
    spec:
      containers:
      - name: eap74-openjdk8-openshift-rhel7
        volumeMounts:
        - mountPath: /var/data
          name: my-volume
      volumes:
      - name: my-volume
        persistentVolumeClaim:
          claimName: my-persistent-volume-claim

Then in the container I copied all of the files in the /opt/eap/standalone/configuration directory to the /var/data directory.

oc exec pod/eap74-openjdk8-openshift-rhel7-5c5486c667-lmzdm -- cp -R /opt/eap/standalone/configuration /var/data

I then used the oc exec command to create an interactive bash shell in the JBOSS pod and removed kubernetes.KUBE_PING from the /var/data/standalone-openshift.xml file.

        <subsystem xmlns="urn:jboss:domain:jgroups:8.0">
            <channels default="ee">
                <channel name="ee" stack="tcp"/>
            </channels>
            <stacks>
                <stack name="tcp">
                    <transport type="TCP" socket-binding="jgroups-tcp"/>
                    <protocol type="kubernetes.KUBE_PING"/> <- removed this line
                    <protocol type="MERGE3"/>
                    <protocol type="FD_SOCK"/>
                    <protocol type="FD_ALL"/>
                    <protocol type="VERIFY_SUSPECT"/>
                    <protocol type="pbcast.NAKACK2"/>
                    <protocol type="UNICAST3"/>
                    <protocol type="pbcast.STABLE"/>
                    <protocol type="pbcast.GMS"/>
                    <protocol type="UFC"/>
                    <protocol type="MFC"/>
                    <protocol type="FRAG3"/>
                </stack>
                <stack name="udp">
                    <transport type="UDP" socket-binding="jgroups-udp"/>
                    <protocol type="kubernetes.KUBE_PING"/> <- removed this line                    
                    <protocol type="MERGE3"/>
                    <protocol type="FD_SOCK"/>
                    <protocol type="FD_ALL"/>
                    <protocol type="VERIFY_SUSPECT"/>
                    <protocol type="pbcast.NAKACK2"/>
                    <protocol type="UNICAST3"/>
                    <protocol type="pbcast.STABLE"/>
                    <protocol type="pbcast.GMS"/>
                    <protocol type="UFC"/>
                    <protocol type="MFC"/>
                    <protocol type="FRAG3"/>
                </stack>
            </stacks>
        </subsystem>

Then I edited the deployment once again, replacing /var/data with /opt/eap/standalone/configuration so that the container has the files in my-persistent-volume-claim mounted to the /opt/eap/standalone/configuration directory in the container.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: eap74-openjdk8-openshift-rhel7
spec:
  template:
    spec:
      containers:
      - name: eap74-openjdk8-openshift-rhel7
        volumeMounts:
        - mountPath: /opt/eap/standalone/configuration
          name: my-volume
      volumes:
      - name: my-volume
        persistentVolumeClaim:
          claimName: my-persistent-volume-claim

At this point, I just want to make sure that the pod is Running and returning the JBOSS welcome page. Problem fixed!

~]$ oc get pods
NAME                                             READY   STATUS    RESTARTS   AGE
eap74-openjdk8-openshift-rhel7-f68b66fc8-jfxww   1/1     Running   0          10m