Elements of CDN Network

For ordinary Internet users, each CDN node is equivalent to a website server placed around it. Through the takeover of dns, the user's request is transparently directed to the nearest node, and the CDN server in the node will be like the original website Like the server, it responds to user requests. Since it is closer to the user, the response time must be faster.


Intelligent scheduling DNS (such as f5's 3DNS)
Intelligent scheduling DNS is a key system in CDN services. When users visit a website that joins CDN services, the domain name resolution request will ultimately be handled by "Smart scheduling DNS". It provides the user with the node address closest to the user through a set of pre-defined strategies, so that the user can get fast service. At the same time, it needs to maintain communication with CDN nodes distributed in various places, track the health status, capacity and other information of each node, and ensure that user requests are distributed to nearby available nodes.
Cache function service
Load balancing equipment (such as lvs, BIG/IP of F5)
Content Cache server (such as squid)
Shared storage


Glossary

CNAME record
CNAME is the alias (Canonical Name); it can be used to resolve a domain name to another domain name. When the DNS system queries the name on the left of CNAME, it will turn to the name on the right of CNAME to query again, and it will trace to the last PTR or A. Name, it will respond after successful query, otherwise it will fail.
For example, if you have a server that stores a lot of information, you use docs.example.com to access these resources, but you want to access these resources through documents.example.com, then you can use your DNS resolution service The supplier adds a CNAME record and points documents.example.com to docs.example.com. After adding this CNAME record, all requests to access documents.example.com will be forwarded to docs.example.com and get the same content.

CNAME domain
When accessing the CDN, after adding the accelerated domain name in the CDN provider console, you will get a CNAME domain name assigned to you by the CDN. You need to add a CNAME record to your DNS resolution service provider and point your accelerated domain name to this CNAME Domain name, so that all requests for this domain name will be directed to the CDN node to achieve acceleration.

DNS
DNS stands for Domain Name System, which means domain name resolution service. Its role on the Internet is to convert the domain name into an IP address that the network can recognize. People are used to remembering domain names, but machines only recognize IP addresses. There is a one-to-one correspondence between domain names and IP addresses. The conversion between them is called domain name resolution. Domain name resolution needs to be completed by a dedicated domain name resolution server. The process is automatic. For example: www.baidu.com entered when surfing the Internet will automatically be converted to 220.181.112.143.

Back to source host
Back-to-origin host: Back-to-origin host decides that the back-to-origin request visits a specific site on the origin site.


Agreement back to source
It means that the protocol used when returning to the source is consistent with the protocol used when the client accesses the resource. That is, if the client uses HTTPS to request the resource, when the resource is not cached on the CDN node, the node will use the same HTTPS method to get the resource back to the source; Similarly, if the client uses the HTTP protocol request, the CDN node also uses the HTTP protocol when returning to the source.