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High allocation can cause frequent collections while post-GC occupancy remains broadly stable. A leak tends to retain objects that should have become unreachable, so compare heap dumps and dominator paths across time. Check allocation rate, live set, GC logs, and process/container memory together before changing heap settings.

Use the system resolver path, for example getent hosts, and compare with a direct DNS query. If a correct address resolves but the connection fails, investigate route, listener, firewall, or protocol behavior. Run diagnostics inside the same container or namespace as the application because resolver configuration may differ.

TCP connection establishment and retransmission make a port-connectivity test meaningful, but application message boundaries still need framing. UDP has no handshake, so silence may mean a dropped packet, invalid request, or a service that does not answer probes. Test using a valid protocol request and inspect both ends when possible.

Look for parent-owned registries, executor queues, thread locals, context class loaders, and callbacks. An unreachable cycle can be collected; a path from a long-lived root cannot.