Custom Repository sync fails with an error 'RPM1004: Error retrieving metadata: A connection error occurred' on Satellite 6 server.

Issue

• Red Hat repositories are syncing with no error but repository from a Custom product which are SSL based are failing.

• While trying to sync Third-party repositories on Red Hat Satellite, it fails with RPM1004: Error retrieving metadata: A connection error occurred.

  2021-10-13T21:07:03 [E|bac|] RPM1004: Error retrieving metadata: A connection error occurred (Katello::Errors::PulpError)
  

• Repository sync for a Custom product based on SSL and certificates signed by DST Root CA X3 fails with the error given below:

  Oct 13 21:06:45 satellite pulp: nectar.downloaders.threaded:ERROR: Skipping requests to customrepo.example.com due to repeated connection failures: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:618)
  
  

• Below error has been observed in the Red Hat Satellite GUI -> Monitor -> Tasks -> Sync task:

  RPM1004: Error retrieving metadata: A connection error occurred
  "error"=>
   {"code"=>"RPM1004",
    "data"=>{"reason"=>"A connection error occurred"},
    "description"=>"Error retrieving metadata: A connection error occurred",