Post-RHEL-patch: application cannot connect to PostgreSQL on dolnxdb099pv:6526 (local access works)

Hi All,

After the recent RHEL OS patching on dolnxdb099pv, the application is no
longer able to connect to the PostgreSQL database on port 6526. The
application fails with the following error:

psycopg2.OperationalError: connection to server at "dolnxdb099pv"
(200.24.1.108), port 6526 failed:
server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.

Important detail: when I log in to the RHEL server directly, I am able to
connect to the database and query it without any issue. The database
instance itself is up and healthy. The failure is only on connections
coming in from the application host.

Since the connection is accepted and then dropped (rather than refused),
this points to something in the network or TLS path rather than the
database engine — most likely a change introduced by the patching, such as:

- firewalld / iptables rules reinstated or reset after the patch
- an OS-level security agent or inspection layer now intercepting the
connection
- an OpenSSL / TLS library update changing the negotiation behaviour for
remote clients
- SELinux policy reapplied after the patch

Could you please check from your side whether the patching activity changed
the host firewall, SELinux state, or any security/network agent
configuration on dolnxdb099pv? I will continue checking the PostgreSQL
server log and pg_hba configuration in parallel and share anything relevant.

This is currently blocking the application, so any quick input would be
appreciated.

*Thanks and Kind Regards,*

*Ashok*

-----------------------

*Ashokkumar Mani **(OCP12c/11g/10g/9i, AWS SAA, M103)*

*INDIA*: No.43, J.R.C Palladio, Billapura cross, Bilichikkanahalli,
Near Indus International School,Bangalore-562125

*Ph:+971 54 723 0075 | Wp*: * +91 81975 99922 *W:
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