Inside a locked-down VPC, behind layers of private subnets, the proxy was the last line standing. This is where security is proven or lost.
A security review of VPC private subnet proxy deployment is not an audit you check off—it is the backbone of resilient cloud infrastructure. A weak proxy in a private subnet turns isolation into illusion. To hold the line, every component must be tested, every route mapped, every ACL and security group verified against intended policy.
Start with isolation. The private subnet must reject all inbound internet traffic outright. Proxies here should be the only controlled exit to the outside world, and only for pre-approved destinations. Confirm outbound traffic filtering at the proxy level, inspect IAM roles with least privilege, and ensure NACLs block unintended ports.
Then harden the proxy. No open administrative ports to the public. Force TLS from clients to the proxy, and from the proxy to targets. Rotate keys and credentials. Apply strict access logging and forward logs to a secure, immutable store with real-time alerting. Any unlogged event is a blind spot.
Evaluate route tables. Private subnets gain internet access only through the proxy’s NAT or explicitly approved egress paths. Review every route to ensure there's no shadow path bypassing proxy inspection.