What Happens at the Proxy?

About this interactive

A proxy is a machine in the middle: the client connects to it, and it makes its own connection onward. What that changes depends on whose side it is on. A forward proxy works for clients. A school or a company sends its users' web traffic through it, so it can filter sites and scan downloads, and the websites see the proxy instead of the user. A firewall rule that lets web traffic out from the proxy alone is what stops users going around it. A reverse proxy works for servers. It sits in front of a bank of web servers, visitors connect to it, and it decides what reaches the servers behind. That lets it take jobs off them: sharing requests among them (load balancing), ending the encrypted session (SSL offloading), keeping copies of popular content (caching), compressing pages, screening requests with a web application firewall, sending visitors to different versions of a page (A/B testing) or checking sign-in. The servers behind it stay out of sight, and if there is only one proxy, the site goes down with it. To predict what happens, find where the proxy sits, ask whose traffic it handles, and follow the request through it.

What you'll learn

Predict what happens to a request when a reverse proxy load balances, ends TLS, caches, compresses, filters with a web application firewall, runs an A/B test or checks sign-in for the servers behind it
Predict what a website sees and what a firewall allows when clients reach the web through a forward proxy, and tell a forward proxy from a reverse proxy by whose side it works for
Explain why the servers behind a reverse proxy are hidden from visitors and scans, and why a single proxy with no standby takes the whole site down when it fails

Aligned to

CompTIA Security+

3.2 Given a scenario, apply security principles to secure enterprise infrastructure.

Key terms

Reverse Proxy: A proxy server positioned in front of backend servers that intercepts client requests to provide load balancing, anonymity, or protection for those servers.
Forward Proxy: A proxy server that sits between clients and the internet, forwarding client requests to external servers on the client's behalf.
Load Balancer: A device or software that distributes incoming network traffic across multiple servers to ensure availability and performance.
SSL Offloading: The practice of terminating SSL/TLS encryption at a proxy or load balancer so that backend servers are relieved of encryption processing overhead.
Caching: The process of storing copies of content on a server so future requests can be served faster without retrieving the original source.
Web Application Firewall: A firewall that filters and monitors HTTP traffic to and from a web application to prevent attacks.
Single Point of Failure: A component within a system whose failure would cause the entire system or service to become unavailable.

Topics

Reverse Proxy Forward Proxy Load Balancer Ssl Offloading Caching Web Application Firewall Interactive Predict

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