DDoS protection strategies in HLD - System Design Guide

Problem Statement

When a service faces a sudden flood of fake traffic from many sources, it becomes overwhelmed and slows down or crashes. This attack, called Distributed Denial of Service (DDoS), makes the service unavailable to real users and can cause financial and reputational damage.

Solution

DDoS protection strategies work by detecting unusual traffic patterns and filtering out malicious requests before they reach the core service. They use layers of defense like traffic rate limiting, IP reputation checks, and traffic scrubbing through specialized networks to keep the service responsive and available.

Architecture

Internet /

Attackers

→CDN / WAF /

↓

Traffic Analysis &

Traffic Analysis &

This diagram shows how incoming internet traffic, including attack traffic, first passes through a CDN or Web Application Firewall (WAF) with DDoS filtering. Suspicious traffic is analyzed and limited before reaching the application servers.

Trade-offs

✓ Pros

→

Reduces service downtime by blocking malicious traffic early.

→

Improves user experience by allowing legitimate traffic through.

→

Scales to handle large attack volumes using cloud-based scrubbing.

→

Can integrate with existing infrastructure like CDNs and firewalls.

✗ Cons

→

Adds latency due to extra traffic inspection steps.

→

May block some legitimate users if detection rules are too strict.

→

Costs increase with higher traffic volumes and advanced filtering.

Use when your service faces or expects high-volume traffic spikes above thousands of requests per second, especially if exposed publicly on the internet.

Avoid if your service has very low traffic (under hundreds of requests per second) or is internal-only, where DDoS risk is minimal and added complexity is unnecessary.

Real World Examples

Netflix

Uses cloud-based DDoS protection integrated with their CDN to absorb and filter massive traffic spikes during popular show releases.

Amazon

Employs multi-layered DDoS defenses including AWS Shield and WAF to protect their e-commerce platform from large-scale attacks.

Cloudflare

Provides global DDoS mitigation by routing traffic through their network and filtering malicious requests before reaching customer servers.

Alternatives

Rate Limiting

Limits the number of requests per user or IP without full traffic scrubbing.

Use when: Choose when attacks are low volume or originate from few sources.

Anycast Network

Distributes traffic across multiple data centers to absorb attacks.

Use when: Choose when you have global infrastructure and want to spread attack load.

Blackhole Routing

Drops all traffic to a target IP during an attack, effectively making it unreachable.

Use when: Choose as a last resort when attack volume is too high to mitigate.

Summary

DDoS protection strategies prevent service outages caused by overwhelming fake traffic.

They filter and limit malicious requests before they reach core servers using multiple defense layers.

Choosing the right strategy depends on traffic scale, attack risk, and infrastructure capabilities.