A study of CDN

Recently in the Learning CDN Some knowledge, here summarizes to share ~ ~

I. INTRODUCTION of CDN

CDN the full name is Content Delivery Network , i.e. Content Distribution Network .

The basic idea is to avoid the bottleneck and link of the Internet which may affect the speed and stability of data transmission, and make the content transmission faster and more stable. By placing node servers throughout the network, a layer of intelligent virtual networks based on existing Internet ,CDN systems can be based on aggregate information, such as network traffic and the connection of each node, the load status, and the distance and response time to the user, re-directs the user's request to the service node closest to the user. The goal is to enable users to get the content they need, solve The congestion of Internet networks, and improve the responsiveness of users to websites.

The core idea is:

A , select the best equipment to provide services to users;

B , if a content is required by many users, it is cached to the node closest to the user;

Second, CDN actual application Scenario 1, no CDN:

Here is a relatively simple example, the actual situation is more complex than this.

users in IE Enter www.taobao.com, click OK, and the local DNS(LDNS) will be requested firstif the local DNS the corresponding DNS records have been cached , the corresponding IPis returned directly ,IE then to the corresponding IP sends a request to get what you want. If the local DNS does not have a cache, the top-level DNS server is polled for lookups.

2. When there is a CDN:

1. user access www.taobao.com, request local DNS resolution domain name www.taobao.com ;

2. local DNS request authoritative dns_1(the original source of the domain name, can be understood as the domain name registration place) to resolve the domain name www.taobao.com;

3. authoritative DNS returns the CNAME of the domain name to the local DNS

(www.gslb.taobao.com.danuoyi.tbcache.com) , as well as the authority responsible for parsing the domain name dns_2 (i.e. GSLB of the IP address). the domain name server that is responsible for parsing the CNAME is pointed to GSLBfirst on the authoritative dns_1 server.

4 . Local DNS request GSLB Resolve domain name www.gslb.taobao.com.danuoyi.tbcache.com;

5 . GSLB According to the domain name, according to the local DNS IP address to determine the user's proximity, server performance, etc.

After comprehensive judgment, select the optimal SLB of the IP , to the local DNS returns the parse result of this domain name;

6 . Local DNS Returns the result of the domain name resolution to the user;

7 . The user is requested to provide service to the server according to the result of the domain name resolution, if the necessary resources exist on the server, then return directly, if not, request the necessary resources to the source site;

the core is GSLB : Global Server Load Balance the abbreviation, meaning the global Load Balancing .

It is followed by a number of server groups of servers, it is responsible for monitoring the status of these servers in real time (number of users, machine performance, response time, etc.), when a request arrives, according to the current request and the server actual situation, will return the best server address, of course, some time may be based on some cost considerations, Turn the request to a lower-cost regional server.

There are many algorithms for load balancing, for example: based on IP , based on IP weighted, geo-based, cost-based, and so on.

GSLB It is generally hierarchical in level:

Third, the noun explanation

1) Edge node: the node closest to the user

2) CNAME: Alias record. This record allows you to map multiple names to the same computer. Typically used for computers that provide both WWW and mail services. For example, there is a computer named "Host.mydomain.com" (a record). It also provides the WWW and mail services, in order to facilitate user access to services. You can set two aliases (CNAME) for this computer: www and mail.

3) domain name Resolution: Domain name Resolution is the conversion process of the domain name to the IP address .

IP address is the network that identifies your site Digital Address , in order to be easy to remember, the use of domain names instead IP address identifies the site address. That is , the process of www.baidu.com à 115.239.210.27.

DNS parsing Process

4) Domain name authorization: Specifies who is the authoritative DNS for the domain name, that is, who is responsible for resolving the domain name (completed by the NS record operation).

5) Authoritative DNS: specifically for the specific domain name has the authority to publish the ability of the DNS, the Internet domain name (domain name records) The origin of the resolution results.

A study of CDN