Proxying is the action of transferring data between a client and a server over two independent connections.

Direction of Communication:

Proxy (Forward Proxy): A proxy typically handles client requests and acts on behalf of clients to access resources on the Internet or other servers. It sits between client devices (e.g., browsers) and the external servers, forwarding client requests to those servers and returning the responses to the clients.

Reverse Proxy: A reverse proxy, on the other hand, handles requests from clients on behalf of backend servers. It sits between clients and the server infrastructure, forwarding client requests to the appropriate backend servers and returning the responses to clients.

Reverse proxy

Why should a reverse proxy be used?

The packet filter itself cannot decide what should be done in application protocols. For such an inspection you can use deep packet inspection or a reverse proxy.

In addition, a reverse proxy can implement protocol specific access control lists as well as other checks to protect the application behind. Such checks are malware, spam, web attack detection and so on.

Warning Reverse proxies support you to prevent common attacks to your web application by bots but will never provide a 100% success rate in detection of bad traffic. Especially a targeted attack will very likely be not detected because a lot of effort has been taken to prevent detection. Do not use a reverse proxy as a replacement / excuse for not fixing the main problems like known vulnerabilities in libraries, outdated software, or vulnerabilities in your own code by updating / removing them or by changing your own code.


Half Termination (TLS Termination at Reverse Proxy)

Incoming TLS traffic is decrypted at the reverse proxy, and the communication with backend servers occurs over an unencrypted channel.

Passthrough (TLS Passthrough or TCP Proxy)

The reverse proxy acts as a pass-through conduit for TLS traffic without decrypting it. This approach is suitable when end-to-end encryption is required and the reverse proxy is only responsible for forwarding traffic.

SNI-Based Routing

SNI (Server Name Indication) can be used by the reverse proxy to terminate TLS and route requests based on the hostname indicated in the SNI extension. SNI-based routing is commonly used in scenarios where multiple SSL/TLS certificates are hosted on the same IP address.