[RH-SSO 7.6.X OpenShift templates] Equip RH-SSO OpenShift templates also spawning a DB pod with default generic DB connection validation checker

Originally initiated by SSOSUP-100 report the RH-SSO OpenShift templates, which besides provisioning a RH-SSO pod also deploy a DB pod, so far doesn't implement a DB connection validation checker. This results in a situation, when the liveness probe on the RH-SSO pod is still returning "HTTP 200/OK" status even with a "database lost" issue.

To improve the UX in this kind of situations, and prevent from templates failure in these specific cases, we should follow the articles about setting DB connection validation checkers by default in the templates:

• https://access.redhat.com/solutions/156103
• https://access.redhat.com/documentation/en-us/red_hat_jboss_enterprise_application_platform/7.3/html/configuration_guide/datasource_management#configure_database_connection_validation_settings

and regardless of the underlying DB driver used in the deployments, deploy a default generic DB connection validation checker, which is able to detect the DB malfunction on the remote end.

For example, even for the Oracle JDBC driver, there's an article / guidance on how to implement a lightweight DB connection socket validation checker:

• https://marschall.github.io/2018/11/22/oracle-lightweight-connection-validation.html

using the generic "org.jboss.jca.adapters.jdbc.extensions.novendor.JDBC4ValidConnectionChecker".

Together with this implementation, we will provide an OpenShift guide update, clarifying on how to switch the default DB connection validation checker to be DB provider specific if desired.