Check env vars, ports, Mongo host name (use service name not localhost), file paths, and logs. ShopNest compose uses mongo:27017 inside the network, not 127.0.0.1 from the host.
EY rounds often probe: Client scenarios.
Themes commonly reported in public MNC interview experiences (AmbitionBox / LinkedIn / Glassdoor-style). Practice aloud; keep answers this short in the real round.