Java Web in-depth analysis (3) CDN

CDN (Content Delivery network) is a kind of advanced traffic distribution network based on the existing Internet. is different from mirroring, equivalent to CDN = Mirror (mirror) +
Cache + Overall load balancing (GSLB). At present, the CDN has cached the static data in the website mainly, such as css,js, picture and static page data, the user requests from the main server to the dynamic page, then downloads these static data from the CDN, thus accelerates the access.

CDN Target:

• Scalability (scalebility) should increase the scalability of large amounts of data, users, and transactions. Provide high-quality content distribution at low cost.
• Security emphasizes security issues.
• Reliability. Disaster tolerance and load balancing.

CDN Architecture:
User to access a hypothetical CSS file, first want to localserver initiating the request, and then iterate to the domain name of the registration server to parse, and then through the CNAME to the CDN Global Load Balancer Server, then the user directly to the CDN node access to this CSS file, If it does not exist, go to the source station request.

3 Types of Load Balancing

• Link load balancing: The DNS server is load balanced and is completed in parsing.
  

• Cluster load balancing: Divided into hardware and software

  - 硬件：非常昂贵的硬件设备，如F5  开始一旦坏掉就GG

  - 软件: 通过代理服务器，可能会增加网络延时。LVS在IP层进行地址转发，HAProxy根据HTTP请求头进行转发。

• Operating System load balancing: Use the soft interrupts and hard interrupts of the operating system to achieve load balancing.

CDN Dynamic Acceleration : This is one of the more popular optimization techniques. The principle is in the CDN DNS resolution through the dynamic link detection technology to find the best path back to the source, and then through the DNS scheduling of all the subsequent requests are selected on this particular path, thereby accelerating the user's access efficiency. So a user in the CDN node across the country in the case of a CDN node after access, you can choose a best source Station link to the user. The simple way is to go to each link to the next file of a specific size, and then find out the least time-consuming link list. In fact, we have to consider the cost of bandwidth and security.

Java Web in-depth analysis (3) CDN