Oracle Database: kggpnpInit: failed to init gpnp (Only one Instance running) 11g,12c,18c,19c

Symptom - 
1.Only one instance of Oracle DB can run on a RAC node (1 or 2)
2. Public interface used as interconnect interface as seen in gv$cluster_interconnects

In Alert log you can see - 
[USER(153710)]CRS-2316:Fatal error: cannot initialize GPnP, CLSGPNP_ERR (Generic GPnP error).
kggpnpInit: failed to init gpnp
  WARNING: No cluster interconnect has been specified. Depending on
           the communication driver configured Oracle cluster traffic
           may be directed to the public interface of this machine.
           Oracle recommends that RAC clustered databases be configured
           with a private interconnect for enhanced security and

           performance.

Reason - From October 2018 PSU of Oracle RAC you must apply OCW component of the GI patch as well to the Oracle Home. 

Example - 
Current  Patch Level 
28790660;OJVM PATCH SET UPDATE 11.2.0.4.190115
28729262;Database Patch Set Update : 11.2.0.4.190115 (28729262)

Solution - Apply OCW Patch

OCW Patch is available as part of GI PSU Bundle, you cannot download it individually (in general)

But you can apply it individually to DB Home

This can be really an issue if you have done newer versions of Oracle install on higher version of Cluster

Patch Apply Process

Step 1 - Stop all Database instances running from the home

Step 2 - Create the ocm file 

$ cd $ORACLE_HOME/ccr/bin

$ ./emocmrsp

(respond <Enter> and then 'Y'>

$ cp ocm.rsp /home/oracle/

Step 3 - Patch Apply 

PrePatch

<Patch Unzipped Location>/<patch_number>/custom/server/<patch_number>/custom/scripts/prepatch.sh -dbhome <oh>

Patch

<oh>/OPatch/opatch apply -oh <oh> -local <Patch Unzipped Location>/<patch_number>/custom/server/<patch_number>

Post Patch

<Patch Unzipped Location>/<patch_number>/custom/server/<patch_number>/custom/scripts/postpatch.sh -dbhome <oh>

Example for Jan 2019 Patch

$ /images/oracle/11.2.0.4/p28729234/28729234/custom/server/28729234/custom/scripts/prepatch.sh -dbhome /opt/oracle/product/112/db

$ /opt/oracle/product/112/db/OPatch/opatch napply -oh /opt/oracle/product/112/db -local /images/oracle/11.2.0.4/p28729234/28729234/custom/server/28729234 -ocmrf /home/oracle/ocm.rsp

$ /images/oracle/11.2.0.4/p28729234/28729234/custom/server/28729234/custom/scripts/postpatch.sh -dbhome /opt/oracle/product/112/db

Final Patch Level
28729234;OCW Patch Set Update : 11.2.0.4.190115 (28729234)
28790660;OJVM PATCH SET UPDATE 11.2.0.4.190115
28729262;Database Patch Set Update : 11.2.0.4.190115 (28729262

Reference Doc ID - 
Customer Recommended11.2.0.4 RAC Database Instance Fails to Start with "No connectivity to other instances in the cluster during startup" After Applying 11.2.0.4 OCT 2018 DB PSU (11.2.0.4.181016 DB PSU) (Patch# 28204707) (Doc ID 2471441.1)