DDoS protection strategies in HLD - Scalability & System Analysis

Scalability Analysis - DDoS protection strategies

Growth Table: DDoS Protection at Different Scales

Users/Traffic	Impact on System	Protection Needs	Typical Solutions
100 users	Normal traffic, no DDoS risk	Basic firewall and rate limiting	Simple IP filtering, basic rate limiting
10,000 users	Higher traffic, occasional spikes	Enhanced rate limiting, anomaly detection	Web Application Firewall (WAF), IP reputation checks
1 million users	High traffic, potential for large DDoS attacks	Distributed mitigation, traffic scrubbing	CDN with DDoS protection, traffic filtering, geo-blocking
100 million users	Massive traffic, frequent large-scale attacks	Global distributed defense, automated mitigation	Multi-layered defense, Anycast networks, cloud-based DDoS protection services

First Bottleneck: Network Bandwidth and Application Servers

At small scale, the system handles traffic normally. As traffic grows, the network bandwidth becomes the first bottleneck because DDoS attacks flood the network with excessive requests.

Application servers also become overwhelmed by processing fake requests, leading to CPU and memory exhaustion.

Without protection, the system becomes unreachable due to network saturation or server overload.

Scaling Solutions for DDoS Protection

• Rate Limiting: Limit requests per IP to reduce flood impact.
• Web Application Firewall (WAF): Filter malicious traffic based on patterns.
• Content Delivery Network (CDN): Distribute traffic globally to absorb attacks.
• Traffic Scrubbing Centers: Redirect traffic through cleaning services to remove malicious packets.
• Anycast Network: Use multiple data centers with the same IP to distribute attack traffic.
• IP Reputation and Geo-blocking: Block traffic from suspicious or high-risk regions.
• Autoscaling: Dynamically add servers to handle traffic spikes.
• Monitoring and Alerting: Detect attacks early and respond quickly.

Back-of-Envelope Cost Analysis

• At 1 million users, assuming 1 request per second per user -> 1 million RPS.
• Single server handles ~5,000 RPS -> need ~200 servers for application layer.
• Network bandwidth: 1 million RPS x 1 KB/request = ~1 GB/s (~8 Gbps).
• Requires multiple 10 Gbps network links and distributed data centers.
• CDN and scrubbing services add cost but reduce load on origin servers.
• Monitoring and mitigation tools require additional compute and storage.

Interview Tip: Structuring DDoS Protection Discussion

Start by explaining what DDoS attacks are and why they impact network and servers.

Discuss scaling challenges at different traffic levels.

Identify the first bottleneck (network bandwidth and server CPU).

Propose layered solutions: rate limiting, WAF, CDN, scrubbing.

Explain trade-offs and cost implications.

Conclude with monitoring and automated response importance.

Self-Check Question

Your database handles 1000 QPS. Traffic grows 10x due to a DDoS attack. What do you do first?

Answer: Implement network-level filtering and rate limiting to block malicious traffic before it reaches the database. Use a CDN or scrubbing service to absorb and filter attack traffic, preventing overload on the database.

Key Result

DDoS attacks first overwhelm network bandwidth and application servers; layered defenses like rate limiting, WAF, CDN, and traffic scrubbing are essential to scale protection effectively.