What is a Proxy?

A proxy is a server or software that sits between a client and a server and acts as an intermediary to facilitate communication between the two. When a client sends a request to a server through a proxy, the proxy receives the request and forwards it to the server on behalf of the client. The server responds to the request by sending its response back to the proxy, which in turn sends the response back to the client.

The term “proxied” is used to describe this process of forwarding requests through a proxy.

Types of Proxies

Forward Proxy (Web Proxy)

A web proxy, also known as a “forward proxy,” forwards requests from a client (e.g., a web browser) to the internet. A forward proxy is typically used to:

• Control access to the internet
• Cache frequently accessed resources to reduce network traffic
• Provide anonymity by hiding the client’s identity
• Enforce security policies and content filtering

Reverse Proxy

A “reverse proxy,” on the other hand, often sits between the internet and a web server or other service and forwards requests from the internet to that service. A reverse proxy is typically used to:

• Improve performance through caching and load balancing
• Enforce security policies and protect backend servers
• Provide load balancing and failover capabilities
• Handle SSL termination and certificate management
• Simplify architecture by providing a single entry point

Proxies in Service Mesh

In the context of service mesh architectures like Istio, proxies play a crucial role:

Envoy Proxy

Envoy Proxy is a popular proxy used for this purpose, especially in service meshes like Istio to mediate traffic between services or, as in the case of Envoy Gateway, at the ingress of a Kubernetes cluster to manage incoming traffic to backend services.

Service Mesh Proxies

In a service mesh, each service typically has a sidecar proxy (like Envoy) that handles:

• Service-to-service communication
• Load balancing and traffic routing
• Security (mTLS, authentication, authorization)
• Observability (metrics, logging, tracing)
• Resilience (circuit breaking, retries, timeouts)

Benefits of Proxying

Security

• Traffic inspection and filtering
• Authentication and authorization
• DDoS protection
• SSL/TLS termination

Performance

• Caching frequently accessed content
• Compression of responses
• Load balancing across multiple servers
• Connection pooling

Reliability

• Failover to backup servers
• Health checking of backend services
• Circuit breaking to prevent cascading failures
• Retry logic for failed requests

Common Use Cases

Web Applications

• CDN (Content Delivery Network) proxies for global content distribution
• API gateways for managing API traffic
• Load balancers for distributing traffic across multiple servers

Microservices

• Service mesh proxies for inter-service communication
• API gateways for external access to services
• Ingress controllers in Kubernetes environments

Enterprise Networks

• Corporate proxies for internet access control
• VPN proxies for secure remote access
• Firewall proxies for network security

Related Concepts

• What is Envoy Proxy? - Learn more about the popular proxy used in service meshes
• What is a Service Mesh? - Understand how proxies work in service mesh architectures
• What is Istio? - Explore how Istio uses proxies for service-to-service communication

Proxying is a fundamental concept in modern networking that enables security, performance, and reliability in distributed systems.