Reverse Proxy

A reverse proxy represents backend servers to their clients. A client connects to the proxy's endpoint, and the proxy communicates with an appropriate backend on the client's behalf. This differs from a forward proxy, which represents clients when they access other systems. Reverse proxies are commonly associated with HTTP applications, but the server-side proxy pattern also applies to database protocols and other network services.

In cloud architectures, a reverse proxy provides a stable access point while backend instances, containers, or database roles change. An HTTP reverse proxy might route requests for one hostname to a web application and requests under an API path to a separate service. Depending on its capabilities, it can terminate TLS, authenticate requests, cache responses, or distribute traffic among healthy targets. These are optional capabilities, not properties of every reverse proxy.

For high availability, deploy the proxy tier across independent failure domains and provide healthy backends in multiple Availability Zones. A single proxy virtual machine can become a single point of failure even when many application servers sit behind it. Health checks should reflect whether a backend can serve useful requests, and connection-draining settings should allow suitable time for in-progress work during deployments. A proxy cannot compensate for an unavailable dependency that has no functioning replacement.

Database proxies illustrate why proxy concepts extend beyond web traffic. Amazon RDS Proxy maintains a pool of database connections that applications can share, reducing connection-establishment overhead and helping absorb connection spikes from workloads such as AWS Lambda. It can direct connections to a new database writer during supported failover scenarios. This improves connection handling and recovery behavior, but does not create database replicas, increase database compute capacity, or guarantee that an in-flight transaction succeeds.

Connection pooling also has limits. Transactions and session-specific state can require a client to remain associated with one database connection, reducing opportunities to share connections. Engineers should monitor connection utilization, wait times, and session pinning rather than assuming that every application connection can be multiplexed freely. For an exam scenario describing frequent short-lived connections overwhelming an otherwise adequately sized database, a database connection proxy is more relevant than an HTTP load balancer.

The extra network hop introduces latency, cost, configuration complexity, and another capacity boundary. Configure connection limits and timeouts across the client, proxy, and backend so that stalled requests do not accumulate indefinitely. Retries need bounded backoff and awareness of operation semantics: automatically retrying a payment request or database write after an ambiguous failure can duplicate work unless the operation is idempotent.

A reverse proxy is not automatically a cache, firewall, or load balancer, although one implementation may perform several of these roles. TLS termination also does not imply encryption from the proxy to the backend; configure that connection separately when required. Restrict backend access so clients cannot bypass the proxy's controls, and trust forwarded client-identity headers only when they come through a controlled proxy path.