Forward & Reverse Proxy
Forward proxy acts for clients (hide identity, filter). Reverse proxy acts for servers (LB, TLS, cache, WAF).
Interview tip Lead with a 30-second definition, then one real system example and name 2–3 designs where Forward & Reverse Proxy is non-negotiable.
① What it is (30 seconds)
Forward proxy acts for clients (hide identity, filter). Reverse proxy acts for servers (LB, TLS, cache, WAF).
② How it works in system design
Forward: corporate proxy, VPN. Reverse: client thinks it talks to one server; nginx/ALB routes to fleet. Reverse proxy enables SSL, compression, rate limit at edge.
Typical placement
Client→Edge / Gateway→Forward→Services→Data stores
③ Concrete system design example
Scenario: All traffic to api.example.com hits nginx reverse proxy → routes /payments to payment cluster, /search to search cluster, blocks admin paths.
④ Important interview Q&A
| Question | Answer |
|---|---|
| Reverse proxy vs API gateway? | Gateway adds auth, composition, developer portal; reverse proxy more transport-focused — often layered together. |
| Forward proxy use? | Outbound filtering, geo bypass, developer debugging (Charles). |
| CDN is reverse proxy? | Yes — edge reverse proxy caching static and cacheable responses. |
⑤ Seen in these system designs
- API Gateway — reverse proxy + logic
- Web Crawler — forward proxy pools
- Chrome Malware — safe browsing proxy
In interviews, after explaining the concept, say: "This shows up directly in …" and link two designs.
⑥ Revision checklist
- Forward vs reverse defined
- SSL termination
- Path-based routing
- CDN relationship