Forward Proxy (正向代理)
Forward proxy can be used by the client to bypass firewall restrictions in order to visit websites that are blocked by school, government, company etc. If a website blocked an IP range from visiting the website, then a person in that IP range can use forward proxy to hide the real IP of the client so that person can visit the website and maybe leave some spam comments. However forward proxy might be detected by the website administrator. There are some paid proxy service that has numerous proxy systems around the world so that they can change your IP address every time your visit a new web page and this makes it harder for website administrators to detect.
Reverse Proxy (反向代理)
Reverse proxy is mainly used by server admins to achieve load balancing and high availability. A website may have several web servers behind the reverse proxy. The reverse proxy server takes requests from the Internet and forward these requests to one of the web servers. Most visitors don’t know websites are using reverse proxy because they usually lack the knowledge and tools to detect it or they simply don’t care about it. Nginx can be acting both a web server and a reverse proxy at the same time. HAProxy is another well-known open-source reverse proxy software.
What’s the difference between Forward Proxy and Reverse Proxy?
The main difference between the two is that forward proxy is used by the client such as a web browser whereas reverse proxy is used by the server such as a web server. Forward proxy can reside in the same internal network as the client, or it can be on the Internet.
CDN (Content Delivery Network)
A content delivery network or content distribution network (CDN) is a geographically distributed network of proxy servers and their data centers. The goal is to provide high availability and high performance by distributing the service spatially relative to end-users. CDNs came into existence in the late 1990s as a means for alleviating the performance bottlenecks of the Internet,[1][2] even as the Internet was starting to become a mission-critical medium for people and enterprises. Since then, CDNs have grown to serve a large portion of the Internet content today, including web objects (text, graphics and scripts), downloadable objects (media files, software, documents), applications (e-commerce, portals), live streaming media, on-demand streaming media, and social media sites.[3]
CDNs are a layer in the internet ecosystem. Content owners such as media companies and e-commerce vendors pay CDN operators to deliver their content to their end users. In turn, a CDN pays ISPs, carriers, and network operators for hosting its servers in their data centers.
CDN is an umbrella term spanning different types of content delivery services: video streaming, software downloads, web and mobile content acceleration, licensed/managed CDN, transparent caching, and services to measure CDN performance, load balancing, Multi CDN switching and analytics and cloud intelligence. CDN vendors may cross over into other industries like security, with DDoS protection and web application firewalls (WAF), and WAN optimization.
Figure: (Left) Single server distribution (Right) CDN scheme of distribution
References
https://www.linuxbabe.com/it-knowledge/differences-between-forward-proxy-and-reverse-proxy
https://en.wikipedia.org/wiki/Content_delivery_network