Question

A web application on server 'app01' cannot reach a backend API service running on 'db02' at port 5432. From app01 you run 'curl -v telnet://db02:5432' and immediately receive 'Connection refused'. Pinging db02 succeeds and DNS resolves correctly. What is the MOST likely cause?

Accepted Answer

The backend service is not listening on port 5432 on db02

Answer

A firewall rule is silently dropping packets destined for port 5432

Answer

There is high packet loss between app01 and db02

Answer

The MTU is mismatched, causing large packets to be fragmented