DNS:
分布式ip到domain name的数据库系统，一种服务。
What is a DNS A record?
IP address, 一般一个网站就是一个a记录，但访问量大的网站也会有多个a记录
What is a DNS C record?
本来域名是doc.example.com
但Cname就是doccument.example.com docs.example.com
The ‘A’ stands for ‘address’ and this is the most fundamental type of DNS record, it indicates the IP address of a given domain. For example if you pull the DNS records of google.com, the ‘A’ record currently returns an IP address of: 172.217.5.78. ‘A’ records only hold Ipv4 addresses, if the site has a Ipv6 address, it will instead use an ‘AAAA’ record.
Example of an A record:
| example.com | record type: | value: | TTL |
|---|---|---|---|
| @ | A | 12.34.56.78 | 14400 |
The ‘@’ here indicates that this is a record for the root domain, and the ‘14400’ value is the TTL (Time To Live), listed in seconds. The default TTL for A records is 14400 seconds. This means that if an A record gets updated, it takes 240 minutes (14400 seconds) to take effect.
The vast majority of websites only have one A record, but it’s possible to have several. Some higher profile websites will have several different A records as part of a technique called round robin load balancing, which can distribute request traffic to one of several IP addresses, each hosting identical content.
what is domain name:
friendly name to an IP address.
https://www.lifewire.com/what-is-a-domain-name-2483189