Proxies and gateways

Proxy and gateway interviews compare forward vs reverse proxies, load balancers, and API gateways by traffic direction, TLS termination, health checks, and failure behavior.

Subtopics: forward and reverse proxies, load balancers, and API gateway at the network edge.

On interviews: place components in a diagram from client to service, explain X-Forwarded-* trust, and describe what happens when an upstream is unhealthy.

Common pitfalls: trusting client IP headers from the open internet, sticky sessions without understanding state, and gateways that become a distributed monolith of business logic.

The trade-off is balancing simplicity, performance, safety, and operability — name which axis you optimized and what cost you accepted.

Checklist:

• Know which hop terminates TLS and validates identity.
• Configure health checks, draining, and failover.
• Keep domain logic in services; gateways for cross-cutting policy.
• Document blast radius when the gateway misroutes.