Building a CDN (Content Delivery Network) server requires selecting a server configuration based on your budget, expected traffic, and performance requirements. Here are some considerations for choosing a server configuration:

　　Bandwidth: CDN servers require high bandwidth to quickly distribute content to users. When choosing a server, make sure it has enough bandwidth to support your traffic needs. With future expansion in mind, choose servers with scalable bandwidth.

　　Storage: CDN servers usually require a large amount of storage space to store static and dynamic content. SSD hard drives are more suitable for CDNs than traditional HDD hard drives because they offer higher read speeds and response times.

　　Memory: Sufficient memory can speed up the caching and distribution of content. Choosing a server with enough memory can improve the performance of your CDN.

　　CPU: CDN servers generally do not require very powerful CPUs because their main task is to cache and distribute content rather than perform complex calculations. Just choose a mid-range CPU.

　　Location: The location of the CDN server is very important. They should be distributed geographically close to users to reduce latency and improve performance. Therefore, consider its data center location when choosing a server hosting provider.

　　CDN software: Choose the appropriate CDN software or service. These software can help you manage content caching, routing and distribution. Some well-known open source CDN software includes Nginx, Varnish, etc.

　　Security: Considering the security risks that CDN may face, choose a server with good security performance and DDoS protection capabilities.

　　Cost: Finally, there is the cost factor to consider. Choose a server configuration based on your budget. Some cloud service providers also provide CDN services, which can be flexibly adjusted according to needs.

　　When choosing a server configuration, it's a good idea to evaluate your needs, including expected traffic, user geography, and content type. Then, work with a server hosting provider or CDN service provider to choose a server configuration that suits your needs. Continuously monitoring and optimizing CDN performance is also key to ensuring good content delivery.