Distributed Denial of Service (DDoS) attacks are one of the most common and damaging threats to modern APIs. By overwhelming your system with massive volumes of traffic, attackers aim to exhaust resources, degrade performance, or take your service completely offline.
A strong DDoS defence is not a single feature—it’s a layered system design strategy. In this post, we’ll walk through practical and widely used techniques to protect your API from DDoS attacks.
A Content Delivery Network (CDN) acts as the first line of defence against DDoS attacks.
Traffic absorption: CDNs distribute traffic across a global network of servers, absorbing large traffic spikes before they reach your origin server.
Caching: Frequently requested content is cached at edge locations, reducing load on your API.
Anycast routing: Requests are routed to the nearest data centre, making it harder for attackers to overwhelm a single location.
Cloudflare can automatically detect volumetric attacks and mitigate them at the network edge, often without your application even noticing the attack.
A Web Application Firewall filters and monitors incoming HTTP/HTTPS requests.
Blocks malicious payloads (SQL injection, XSS, malformed requests).
Applies rate limits to API endpoints.
Uses managed rulesets to detect known attack patterns.
Enable rate-based rules for sensitive endpoints.
Customize rules for your API paths (e.g., /login, /payments).
Log blocked requests for analysis and tuning.
A WAF prevents attackers from abusing application-level vulnerabilities during a DDoS attack.
CAPTCHAs help distinguish between real users and automated traffic.
Stops bot-driven attacks at the edge.
Prevents brute-force and credential-stuffing attacks.
Reduces unnecessary load on backend services.
On authentication endpoints
On suspicious traffic patterns
After a rate-limit threshold is exceeded
For APIs, CAPTCHAs are often combined with challenge-based responses or token validation instead of traditional UI CAPTCHAs.
Autoscaling ensures your infrastructure can handle traffic spikes—both legitimate and malicious.
Automatically increases compute resources under load.
Prevents service crashes during sudden traffic surges.
Maintains availability during partial attacks.
Autoscaling alone is not protection. Without rate limits or WAF rules, autoscaling can significantly increase cloud costs during an attack. Always combine it with traffic filtering mechanisms.
IP blocking allows you to deny traffic from known malicious sources.
Quickly blocks attackers once identified.
Can be applied at CDN, WAF, load balancer, or application level.
Attackers often rotate IPs.
Ineffective against large botnets.
Use IP blocking as a reactive measure, combined with automated detection systems and short-lived block rules.
Geo blocking restricts traffic based on geographic location.
Reduces attack surface if your API serves limited regions.
Stops attacks originating from countries where you have no users.
Internal or regional APIs
Compliance-driven restrictions
Emergency mitigation during active attacks
Geo blocking should be carefully applied to avoid blocking legitimate users or VPN traffic.
Protecting your API from DDoS attacks requires a defense-in-depth approach. No single solution is enough on its own. By combining multiple layers—CDN protection, WAF rules, CAPTCHAs, autoscaling, IP blocking, and geo blocking—you significantly reduce both the likelihood and impact of attacks.
A well-designed system:
Filters malicious traffic early
Scales safely under pressure
Preserves performance for legitimate users
Controls operational costs during attacks
DDoS resilience is not optional—it’s a core part of modern system design.