Proxy Fundamentals

🔄 Proxies in Distributed Systems #

🧭 Introduction #

Modern distributed systems rely on proxies to manage complexity, enhance security, and improve performance. In microservice architectures, proxies play a crucial role in service discovery, load balancing, and API gateway functionality.

A proxy serves as an intermediary that sits between clients and servers, intercepting and potentially modifying the communication between them. This pattern enables numerous architectural benefits that we’ll explore in this lecture.

🛡️ What is a Proxy? #

A proxy is an intermediary server that acts on behalf of another entity in a network communication. It intercepts requests, may transform them, and forwards them to the appropriate destination.

Proxies serve several key purposes in distributed systems:

  • Abstraction: Hide implementation details of backend services
  • Security: Filter traffic and protect backend services
  • Performance: Cache responses and optimize data transfer
  • Routing: Direct traffic based on content or request patterns
  • Monitoring: Log and analyze traffic patterns

🔄 Forward Proxy #

A forward proxy acts on behalf of the client. It sits between clients and the wider internet, forwarding client requests to external servers.

Characteristics: #

  • The client is aware of the proxy and must be configured to use it
  • Commonly used for access control, content filtering, and anonymity
  • Hides the client’s identity from the server
  • Often deployed in corporate or educational networks

Key Use Cases: #

  • Internet access control in organizations
  • Content filtering for compliance or security
  • Anonymizing client traffic for privacy
  • Caching frequently accessed content to improve performance
  • Bypassing geo-restrictions on content

🌐 Diagram # 

                                 INTERNET
                                    |
                                    |
+------------------+        +---------------+        +------------------+
|                  |        |               |        |                  |
|   Client 1   ----+------->|               |------->|   Web Server 1   |
|                  |        |               |        |                  |
+------------------+        |               |        +------------------+
                           |               |
+------------------+        |   FORWARD    |        +------------------+
|                  |        |    PROXY     |        |                  |
|   Client 2   ----+------->|               |------->|   Web Server 2   |
|                  |        |               |        |                  |
+------------------+        |               |        +------------------+
                           |               |
+------------------+        |               |
|                  |        |               |
|   Client 3   ----+------->|               |
|                  |        |               |
+------------------+        +---------------+
                                    ^
                                    |
                           PRIVATE NETWORK

🔍 How Forward Proxies Work #

  1. Client Configuration: The client is explicitly configured to send requests through the proxy
  2. Request Interception: The proxy receives the client’s request
  3. Policy Enforcement: The proxy applies access control and filtering policies
  4. Request Forwarding: If allowed, the proxy forwards the request to the destination server
  5. Response Processing: The proxy receives the server’s response, potentially caches it
  6. Client Delivery: The proxy returns the response to the client

🧠 Key Concepts to Remember #

  • Forward proxies are client-facing intermediaries
  • They require explicit client configuration
  • They’re excellent for access control and content filtering
  • They hide client identity from destination servers
  • Common implementations include Squid, TinyProxy, and NGINX (when configured as a forward proxy)

In the next section, we’ll explore Reverse Proxies and their critical role in modern microservice architectures.