Backend interview prep

Start

Proxy vs Reverse Proxy Interview Questions and Answers

Learn Proxy vs Reverse Proxy with 10 interview questions, Mermaid diagrams, production scenarios, Spring Boot examples, and enterprise architecture best practices.

Proxy vs Reverse Proxy - Interview Questions & Answers

Proxy Servers and Reverse Proxy Servers are fundamental components of modern enterprise architectures. They improve security, performance, scalability, availability, and traffic management.

Almost every production application uses a reverse proxy such as NGINX, HAProxy, Apache HTTP Server, Traefik, or cloud-native services like AWS Application Load Balancer (ALB).

Q1. What is a Proxy Server?

Answer

A Proxy Server (Forward Proxy) acts as an intermediary between a client and the internet.

Instead of the client directly communicating with external servers, requests first go through the proxy server.

Forward Proxy Architecture

flowchart LR
A[Client] --> B[Forward Proxy] --> C[Internet] --> D[Website]

Common Uses

  • Hide client IP
  • Content filtering
  • Internet access control
  • Corporate internet security
  • Anonymous browsing

Q2. What is a Reverse Proxy?

Answer

A Reverse Proxy sits in front of one or more backend servers.

Clients communicate only with the reverse proxy, which forwards requests to the appropriate backend server.

Reverse Proxy Architecture

flowchart LR
A[Client] --> B[Reverse Proxy]

B --> C[Spring Boot Service 1]

B --> D[Spring Boot Service 2]

B --> E[Spring Boot Service 3]

Common Uses

  • Load Balancing
  • SSL Termination
  • Authentication
  • Caching
  • API Routing
  • Security

Q3. What is the difference between Proxy and Reverse Proxy?

Answer

Proxy Server Reverse Proxy
Represents clients Represents servers
Client-side component Server-side component
Hides client identity Hides server identity
Controls outgoing traffic Controls incoming traffic
Used inside organizations Used in data centers and cloud

Comparison

flowchart TD
A[Forward Proxy]

A --> B[Protect Clients]

C[Reverse Proxy]

C --> D[Protect Servers]

Q4. How does a Forward Proxy work?

Answer

The client sends requests to the proxy.

The proxy:

  • Verifies policies
  • Filters requests
  • Sends requests to the destination server
  • Returns responses to the client

Flow

sequenceDiagram
participant Client
participant Proxy
participant Internet
Client->>Proxy: Request
Proxy->>Internet: Forward Request
Internet-->>Proxy: Response
Proxy-->>Client: Response

Benefits

  • Privacy
  • Internet Filtering
  • Access Control

Q5. How does a Reverse Proxy work?

Answer

Clients never communicate directly with backend servers.

The reverse proxy:

  • Accepts incoming requests
  • Chooses a backend server
  • Forwards the request
  • Returns the response

Reverse Proxy Flow

sequenceDiagram
participant Client
participant ReverseProxy
participant Backend
Client->>ReverseProxy: HTTP Request
ReverseProxy->>Backend: Forward Request
Backend-->>ReverseProxy: Response
ReverseProxy-->>Client: Response

Benefits

  • High Availability
  • Security
  • Scalability

Q6. Why do Spring Boot Microservices use Reverse Proxy?

Answer

Reverse proxies provide centralized traffic management.

Enterprise Architecture

flowchart TD
A[Users] --> B[Internet] --> C[NGINX / API Gateway]

C --> D[Order Service]

C --> E[Payment Service]

C --> F[Inventory Service]

C --> G[Notification Service]

Advantages

  • Single Entry Point
  • SSL Termination
  • Authentication
  • Rate Limiting
  • Load Balancing

Q7. What are the advantages of Reverse Proxy?

Answer

Advantages

  • Load Balancing
  • SSL Offloading
  • Security
  • Caching
  • Compression
  • API Routing
  • High Availability
  • Hides Backend Servers

Features

mindmap
  root((Reverse Proxy))
    Load Balancing
    SSL Termination
    Security
    Caching
    Compression
    API Routing
    Monitoring

Q8. What is SSL Termination?

Answer

SSL Termination means the Reverse Proxy decrypts HTTPS traffic before forwarding requests to backend services.

SSL Termination

flowchart LR
A[Client] --> B[HTTPS]

B --> C[Reverse Proxy]

C --> D[HTTP or HTTPS]

D --> E[Spring Boot]

Benefits

  • Reduces CPU usage on backend servers
  • Simplifies certificate management
  • Centralizes TLS configuration

Note: In high-security environments, traffic between the reverse proxy and backend services may also remain encrypted using HTTPS or mTLS.

Q9. What are common Reverse Proxy implementations?

Answer

Popular Reverse Proxy solutions include:

  • NGINX
  • HAProxy
  • Apache HTTP Server
  • Traefik
  • Envoy Proxy
  • AWS Application Load Balancer
  • Azure Application Gateway

Reverse Proxy Ecosystem

flowchart TD
A[Reverse Proxy]

A --> B[NGINX]

A --> C[HAProxy]

A --> D[Traefik]

A --> E[Envoy]

A --> F[AWS ALB]

Q10. What are the enterprise best practices for Reverse Proxy?

Answer

Follow these best practices:

  • Place Reverse Proxy behind a Firewall.
  • Enable HTTPS/TLS 1.3.
  • Use Web Application Firewall (WAF).
  • Configure Rate Limiting.
  • Enable Request Logging.
  • Use Health Checks.
  • Configure Load Balancing.
  • Enable Compression and Caching.
  • Protect backend servers from direct internet access.
  • Monitor traffic continuously.

Enterprise Architecture

flowchart TD
A[Users] --> B[Firewall] --> C[Web Application Firewall] --> D[Reverse Proxy]

D --> E[API Gateway]

E --> F[Spring Boot Microservices]

F --> G[Database]

Production Request Flow

flowchart LR
A[Client] --> B[Reverse Proxy] --> C[Authentication] --> D[Load Balancer] --> E[Spring Boot Service] --> F[Database]

Enterprise Network Components

mindmap
  root((Enterprise Network))
    Firewall
    Reverse Proxy
    API Gateway
    Load Balancer
    WAF
    TLS
    Monitoring
    Logging

Senior Interview Tip

Many candidates confuse Reverse Proxy, Load Balancer, and API Gateway.

Remember:

Component Primary Responsibility
Forward Proxy Protects and manages clients
Reverse Proxy Protects and routes to backend servers
Load Balancer Distributes traffic across multiple servers
API Gateway API routing, authentication, rate limiting, and policy enforcement

In modern enterprise architectures, these components often work together:

  • Firewall
  • Web Application Firewall (WAF)
  • Reverse Proxy (NGINX/Envoy)
  • API Gateway
  • Load Balancer
  • Spring Boot Microservices
  • Service Mesh (Istio/Linkerd)

Quick Revision

  • A Forward Proxy represents clients.
  • A Reverse Proxy represents servers.
  • Reverse Proxies hide backend servers.
  • NGINX and HAProxy are common Reverse Proxy solutions.
  • Reverse Proxies support SSL termination, caching, and routing.
  • Reverse Proxies improve scalability and availability.
  • Protect Reverse Proxies using Firewalls and WAF.
  • Use health checks and load balancing in production.
  • Keep backend services inaccessible from the public internet.
  • Reverse Proxy is a core building block of modern microservices architectures.