Choose the right private connection

Do not start with a service name. First ask where traffic must go: one AWS service, one vendor service, the general internet, another network, or an on-premises site.

Then record what the path must provide. Does it need private IP addresses, encryption, broad two-way routing, predictable throughput, or a second independent path? These are separate requirements.

A gateway endpoint gives selected route tables private access to supported services such as S3 and DynamoDB. An interface endpoint places network interfaces in your subnets and can reach an AWS or PrivateLink service.

A NAT gateway provides general outbound translation for private IPv4 workloads. It does not authorize an AWS API call and does not publish a private service for inbound use.

For every flow, write the expected DNS answer and next hop. A path described only as “private” is too vague to test: the endpoint, route table, tunnel, or dedicated link must be named.

Choose the narrowest connection that satisfies the destination. For one S3 bucket, a gateway endpoint plus identity, endpoint, and bucket policies avoids general internet egress.

For one vendor API exposed through AWS PrivateLink, use an interface endpoint. PrivateLink exposes the selected service; it does not create broad, transitive routing between consumer and provider networks.

An interface endpoint still has gates. The service name must resolve to endpoint addresses, the endpoint security group must allow the caller, and the endpoint policy must allow the request. IAM and resource policies still decide authorization.

Use NAT when workloads genuinely need general outbound access to public destinations. NAT solves translation and reachability, not least privilege.

If the requirement changes from one service to broad bidirectional connectivity, choose a routed network design instead. Route scope is itself a security decision.

A private address does not prove private service use. Test DNS from the real subnet, record the selected route, and make one nearby unauthorized request. The successful request proves reachability; the failed request proves scope.

A Site-to-Site VPN creates encrypted IPsec tunnels. Both tunnel health and matching forward and return routes matter.

AWS Direct Connect provides a dedicated connection with more consistent network behavior, but basic Direct Connect is not encrypted by default. Add VPN over Direct Connect, supported MACsec, or application TLS when encryption is required.

One Direct Connect connection or one location is not high availability. A second path counts only when it is physically independent, has usable routes, and carries traffic after the first path fails.

Start with VPN when quick encrypted connectivity is decisive. Add Direct Connect when measured throughput or consistency justifies its cost and lead time.

Test by disabling the active tunnel or connection. Confirm that both forward and return routes move to the independent path and the application still meets its objective.

Route advertisements are also a security boundary. Advertise and accept only approved prefixes, then verify the return advertisement. Encryption protects bytes in transit; it does not authorize every network that becomes reachable.