Follow the forwarding decision
The packet leaves the pod network, passes through the node's forwarding path and reaches the VPC's virtual routing machinery. The source subnet route table must have a destination route matching 10.72.0.0/16, pointing to an appropriate private connection. That might be a VPC peering connection, a transit gateway attachment or another approved network design. A default route to an internet gateway does not automatically make a private database address globally reachable.
Now follow the network hop into the other region. A VPC peering connection carries private traffic between two supported VPCs, including across regions, but each side needs the correct route entries. Peering is not transitive. If VPC A peers with B, and B peers with C, A cannot assume it can reach C through B. A transit gateway can simplify routing across many attached VPCs, but it brings its own attachment, route-table and peering configuration. Those are decisions, not invisible network magic.
At the destination, inspect ingress policies for the actual observed source, after any permitted address translation. The database or proxy may have a security group admitting one node CIDR but not a new pod CIDR. A network ACL can reject packets in one direction because its rules are stateless. Security groups on AWS are stateful, but being allowed through one control does not override a deny in another. If the SYN reaches the destination and the SYN-ACK does not return, investigate reverse routing and stateless response-port rules instead of changing application connection pooling.
This is why a one-way architecture diagram is insufficient. The return path also needs a route to the source address the destination actually sees. If an SNAT gateway changes the source, the reply follows the translated source. If the design preserves the pod source, the return routing must understand that prefix. Asymmetric routing through stateful middleboxes can break flows even if forward and return routes each appear valid in isolation.
The address collision nobody spotted
The interviewer now tells you that an acquired service already uses 10.24.0.0/16 in its destination VPC. An overlapping private CIDR does not merely create a cosmetic naming conflict. Ordinary direct VPC peering cannot be established between VPCs with overlapping CIDRs on AWS. A router may consider 10.24.4.8 local when you meant a remote endpoint. A workaround needs an explicit design, such as renumbering, an intermediary service endpoint, or carefully controlled translation, not a broader 0.0.0.0/0 rule.
That changes the design decision. For a single database service, exposing a narrow, authenticated private service endpoint may be safer than granting two entire networks broad connectivity. A database proxy or managed private endpoint can give consumers a routable interface without requiring every client to know the underlying database CIDR. But confirm the product's cross-region support and initiation direction, rather than treating all private endpoint products as interchangeable.
How I would investigate
I would resolve the database name from the failing pod, record A and AAAA answers, then inspect the resulting source and destination addresses. Next, compare a failing pod with a working one using the exact destination port. If failures are confined to one namespace, inspect the NetworkPolicies selecting those pods, including DNS and database egress, and confirm the network plugin actually enforces them. Check the CNI egress behavior, source subnet route table, private-connection attachment state, destination subnet routing, security policies and return path. VPC flow logs and packet captures, where supported, can distinguish drops, missing responses and successful handshakes followed by TLS or application failures. Flow logs are evidence with collection limits, not a guarantee of recording every packet.
Finally, validate the application's authentication and TLS endpoint name. An open TCP connection does not prove a usable database session. The key interview skill is drawing a packet-level path with a verifiable route and security decision at every boundary. Once those facts are known, adding a gateway, relaxing a firewall or changing a timeout stops being guesswork.
