CDNs ensure consistent uptime for critical websites through redundancy, load balancing, DDoS protection, caching, and global server distribution. Redundancy prevents single points of failure by routing traffic to backup servers in different locations. Load balancing distributes traffic evenly to avoid overloads. DDoS attacks are mitigated via rate limiting, WAFs, and Anycast routing. Intelligent caching at edge servers reduces origin server dependency. Continuous health monitoring and automatic failover redirect traffic instantly when issues occur. Global distribution lowers latency and regional outages, with well-managed CDNs capable of achieving over 99.9% uptime. These features make CDNs essential for mission-critical online services.