Forward Proxy

A forward proxy acts on behalf of clients rather than the servers they contact. A workload connects to the proxy, and the proxy establishes a separate connection to the destination. This creates a policy enforcement point between internal applications and external services. A reverse proxy serves the opposite role: it receives requests on behalf of destination applications. The distinction is about which side the intermediary represents, not whether it runs in a public or private subnet.

Forward proxies commonly control outbound HTTP and HTTPS traffic. An explicit proxy requires clients to know its address, typically through application settings, proxy environment variables, or automatic configuration. Support varies by application and library; setting HTTPS_PROXY does not guarantee that every process uses it. A transparent deployment steers traffic through a compatible interception appliance without explicit client configuration, but requires careful routing and protocol support. An ordinary HTTP proxy cannot become a transparent proxy merely by making it a route-table target.

For example, build workers in private AWS subnets might need access to approved package repositories but not arbitrary internet destinations. Engineers can run proxy software on Amazon EC2, configure the workers to use its private endpoint, and restrict workload egress to that endpoint and other required private services. The proxy permits approved repository destinations and denies other requests. Its own internet connectivity can use a public NAT gateway or another suitable egress design. Workloads should not retain an alternative unrestricted internet path over either IPv4 or IPv6.

HTTPS requires particular care. With HTTP CONNECT, the proxy can authorize a tunnel using the requested destination hostname and port, but the application payload remains encrypted between client and server. The proxy cannot automatically inspect URL paths, headers, or downloaded files inside that tunnel. TLS interception requires terminating client TLS and creating a separate upstream TLS connection. Clients must trust the inspection certificate authority, and certificate pinning or mutual TLS can make interception incompatible with an application. Inspection also introduces privacy, certificate-management, and compliance obligations.

A NAT gateway is not a forward proxy: it translates network addresses without providing application-aware request authorization. AWS Network Firewall can enforce network and supported application-layer policies, but it is not an explicit HTTP proxy endpoint. Gateway Load Balancer distributes traffic to compatible network appliances; the appliances, not the load balancer, supply inspection or proxy behavior. These components can complement a forward proxy rather than replace its specific functions.

Operationally, deploy enough proxy capacity across Availability Zones, monitor connection counts and resource usage, and test failover behavior. Decide whether failures must block outbound access rather than permit bypass. Protect against becoming an open proxy by restricting reachable clients, authenticating where appropriate, and denying unnecessary destinations, including sensitive internal addresses. Centralized egress improves policy consistency and auditability, but adds latency, processing costs, and a shared dependency. Proxy logs should capture useful policy decisions while protecting credentials and sensitive request data.