Proxies §

Proxies are a fundamental unit in system design with many uses. There are two types of proxies - Forward Proxies and Reverse Proxies. Many people refer to just “proxies” - this is almost always the forward type.

Forward Proxies §

graph LR
	Client --> id[Forward Proxy]
	id[Forward Proxy] --> Server
	Server --> id[Forward Proxy]
	id[Forward Proxy] --> Client

• Sits inbetween clients and servers
• Is a server which acts on behalf of the client
• Client IP is typically masked
• A good example of this is a VPN
• Servers are not aware of forward proxies

Reverse Proxies §

graph LR
	Client --> id[Reverse Proxy]
	id[Reverse Proxy] --> Server
	Server --> id[Reverse Proxy]
	id[Reverse Proxy] --> Client

• Similar to forward proxies but acts on behalf of the server instead
• Clients are not aware of reverse proxies - a DNS request for google.com might hit a reverse proxy, and clients don’t realise this

These have multiple uses:

• Request filtering
• Logging/metrics
• Caching
• Load balancing

An example of a popular proxy is Nginx, which is a webserver often used for this purpose.