Core Concepts
CDN (Content Delivery Network) is a group of distributed servers located in multiple geographic locations that work together to provide fast, highly available, and secure internet content delivery services. The main goal of CDN is to reduce network latency and bandwidth consumption by storing content on edge servers close to end users, thereby improving user experience.
How It Works
When a user visits a website using CDN, CDN intelligently routes the user's request to the nearest edge node based on factors such as user location, network conditions, and server load. This process includes:
- DNS Resolution: When a user accesses a website, the DNS server returns the IP address of the CDN node
- Content Caching: The CDN edge node checks if it has cached content
- Origin Request: If the cache misses, the edge node requests content from the origin server
- Content Delivery: After obtaining the content, the edge node caches it and returns it to the user
- Subsequent Requests: Subsequent requests for the same content are returned directly from the edge node
Key Technologies
Caching Strategies
- TTL (Time To Live): Controls how long content stays cached on CDN nodes
- Cache Keys: Generate unique identifiers based on URL, request headers, etc.
- Cache Hierarchy: Edge cache, regional cache, origin cache
Load Balancing
- Geographic Routing: Select the nearest node based on user location
- Health Checks: Monitor node status and automatically remove failed nodes
- Traffic Scheduling: Dynamically allocate traffic based on node load
Security Mechanisms
- DDoS Protection: Distributed defense against large-scale attacks
- WAF (Web Application Firewall): Filter malicious requests
- HTTPS Support: Provide SSL/TLS encrypted transmission
Advantages
- Reduced Latency: Users get content from nearby nodes, reducing transmission distance
- Reduced Origin Load: Most requests are handled by CDN nodes
- Improved Availability: Distributed architecture provides redundancy
- Bandwidth Cost Savings: Reduces origin server bandwidth consumption
- Enhanced Security: Provides an additional layer of security protection
Use Cases
- Static Resource Acceleration: Images, CSS, JavaScript, and other static files
- Video Streaming: Live streaming, on-demand video content delivery
- Software Distribution: App downloads, update package distribution
- API Acceleration: API response caching and acceleration
- Full Site Acceleration: Comprehensive acceleration for dynamic and static content
Common CDN Providers
- Cloudflare: Global coverage with free tier available
- Akamai: Industry leader with enterprise solutions
- AWS CloudFront: Tight integration with AWS services
- Alibaba Cloud CDN: Extensive domestic coverage in China
- Tencent Cloud CDN: Strong advantages in game acceleration
Interview Points
When answering this question, focus on:
- Definition and core goals of CDN
- Clear description of how it works
- Understanding of key technical points
- Examples of practical use cases
- Differences from traditional direct access