# Reverse proxy (web server)

> From [The System Design Primer](https://github.com/donnemartin/system-design-primer) by Donne Martin, licensed under CC BY 4.0, arranged into chapters for this site. Part of "Building blocks". Web page: https://system.tangentbyte.com/learn/reverse-proxy-web-server

![Diagram](https://system.tangentbyte.com/repo/images/n41Azff.png)\
_[Source: Wikipedia](https://upload.wikimedia.org/wikipedia/commons/6/67/Reverse_proxy_h2g2bob.svg)_

A reverse proxy is a web server that centralizes internal services and provides unified interfaces to the public. Requests from clients are forwarded to a server that can fulfill it before the reverse proxy returns the server's response to the client.

Additional benefits include:

- **Increased security** - Hide information about backend servers, blacklist IPs, limit number of connections per client

- **Increased scalability and flexibility** - Clients only see the reverse proxy's IP, allowing you to scale servers or change their configuration

- **SSL termination** - Decrypt incoming requests and encrypt server responses so backend servers do not have to perform these potentially expensive operations
  - Removes the need to install [X.509 certificates](https://en.wikipedia.org/wiki/X.509) on each server

- **Compression** - Compress server responses

- **Caching** - Return the response for cached requests

- **Static content** - Serve static content directly

  - HTML/CSS/JS
  - Photos
  - Videos
  - Etc

### Load balancer vs reverse proxy

- Deploying a load balancer is useful when you have multiple servers. Often, load balancers route traffic to a set of servers serving the same function.
- Reverse proxies can be useful even with just one web server or application server, opening up the benefits described in the previous section.
- Solutions such as NGINX and HAProxy can support both layer 7 reverse proxying and load balancing.

### Disadvantage(s): reverse proxy

- Introducing a reverse proxy results in increased complexity.
- A single reverse proxy is a single point of failure, configuring multiple reverse proxies (ie a [failover](https://en.wikipedia.org/wiki/Failover)) further increases complexity.

### Source(s) and further reading

- [Reverse proxy vs load balancer](https://www.nginx.com/resources/glossary/reverse-proxy-vs-load-balancer/)
- [NGINX architecture](https://www.nginx.com/blog/inside-nginx-how-we-designed-for-performance-scale/)
- [HAProxy architecture guide](http://www.haproxy.org/download/1.2/doc/architecture.txt)
- [Wikipedia](https://en.wikipedia.org/wiki/Reverse_proxy)