Proxies

What is a reverse proxy? How is it different from a load balancer?

What is a service mesh? Why would you use one instead of implementing retry/timeout logic in your application code?

How does Envoy implement circuit breaking? What configuration parameters matter?

A request enters your system through a public API gateway, routes to a backend service, which calls two downstream services. One downstream call times out. What does the end-user experience?

Describe how you would implement request mirroring (shadow traffic) and what you would use it for.

Not preserving the original client IP after proxying

Symptom: Rate limiting, geo-routing, and access logs all show the proxy IP instead of the real client IP.

Not handling keep-alive connections correctly

Symptom: New TCP connections are created for every request; latency spikes and the file-descriptor limit is hit under load.

Buffering the entire response body before forwarding

Symptom: Large file downloads or streaming responses are delayed until the entire body is received from the upstream; memory usage spikes.

Forwarding sensitive headers (Authorization, Cookie) to untrusted upstreams

Symptom: Credentials leak to backend services that should not have them.

Infinite redirect loops between proxy and backend

Symptom: Requests result in a 301/302 loop; browser or client reports "too many redirects".

Proxy Types: Forward Proxy vs Reverse Proxy vs Service Mesh Sidecar

Proxies sit in the data path and add capabilities like caching, TLS termination, authentication, and observability. Where the proxy sits defines what it can see and control.