Chapter 9: Domain Name System (DNS) and Amazon Route 53

1. C. An AAAA record is used to route traffic to an IPv6 address, whereas an A record is used to route traffic to an IPv4 address.

• AAAA record是为ipv6设置的
• A record 是为ipv4准备的

2. B. Domain names are registered with a domain registrar, which then registers the name
   to InterNIC.

• 域名注册商提供域名注册服务；

3. C. You should route your traffic based on where your end users are located. The best
   routing policy to achieve this is geolocation routing.

• 如果按照位置访问，最好的 route policy就是 geolocation routing
• routing policy：
• Simple—Most commonly used when you have a single resource that performs a given
  function for your domain
• Weighted—Used when you want to route a percentage of your traffic to one particular
  resource or resources
• Latency-Based—Used to route your traffic based on the lowest latency so that your
  users get the fastest response times
• Failover—Used for DR and to route your traffic from your resources in a primary
  location to a standby location
• Geolocation—Used to route your traffic based on your end user’s location

4. D. A PTR record is used to resolve an IP address to a domain name, and it is commonly referred to as “reverse DNS.”

• PTR record用来解析IP地址到域名，或者称作 reverse DNS

5. B. You want your users to have the fastest network access possible. To do this, you would use latency-based routing. Geolocation routing would not achieve this as well as latency based routing, which is specifically geared toward measuring the latency and thus would direct you to the AWS region in which you would have the lowest latency.

• geolocation policy无法保证低延迟，直接使用低延迟策略，会将最低延迟的服务路由给客户；

6. C. You would use Mail eXchange (MX) records to define which inbound destination mail
   server should be used.

• MX records是邮件交换服务用的；

7. B. SPF records are used to verify authorized senders of mail from your domain.

• SPF records是反垃圾邮件的records；

8. B. Weighted routing would best achieve this objective because it allows you to specify
   which percentage of traffic is directed to each endpoint.

• 基于权重的路由策略可以将流量按照比重分流到不同的服务区域；

9. D. The start of a zone is defined by the SOA; therefore, all zones must have an SOA
   record by default.

• SOA records是默认的区域的默认records（start of authority record),）

10. D. Failover-based routing would best achieve this objective.

• 容灾只用使用failover的路由策略；

11. B. The CNAME record maps a name to another name. It should be used only when there are no other records on that name.

• cname records可以将域名指向另外一个域名；

12. C. Amazon Route 53 performs three main functions: domain registration, DNS service,
    and health checking.

• R53支持三个主要功能：域名注册、DNS解析和健康检查，不支持负载均衡！！

13. A. A TXT record is used to store arbitrary and unformatted text with a host.

• txt record从来存储域名的描述信息；

14. C. The resource record sets contained in a hosted zone must share the same suffix.

• 一个域名zone内必须是后缀相同；

15. B. DNS uses port number 53 to serve requests.

• DNS解析用的端口是53

16. D. DNS primarily uses UDP to serve requests.

• DNS解析主要是UDP协议

17. A. The TCP protocol is used by DNS server when the response data size exceeds 512 bytes or for tasks such as zone transfers.

• TCP协议被启用返回请求，当数据大于512B

18. B. Using Amazon Route 53, you can create two types of hosted zones: public hosted
    zones and private hosted zones.

• 使用R53你可以创建公网域名和内网域名；

19. D. Amazon Route 53 can route queries to a variety of AWS resources such as an Amazon CloudFront distribution, an Elastic Load Balancing load balancer, an Amazon EC2 instance, a website hosted in an Amazon S3 bucket, and an Amazon Relational Database (Amazon RDS).

• R53是没法把请求转发到一个解决方案。智能转发到具体的端口服务商；

20. D. You must first transfer the existing domain registration from another registrar to
    Amazon Route 53 to configure it as your DNS service.

• 只有将域名转移到R53，才能使用后续的R53服务；

知识点总结

• Understand what DNS is. DNS is the methodology that computers use to convert humanfriendly domain names (for example, amazon.com) into IP addresses (such as 192.0.2.1).

• 理解什么是DNS。DNS是计算机将域名转换成IP服务；

• Know how DNS registration works. Domains are registered with domain registrars that
  in turn register the domain name with InterNIC, a service of ICANN. ICANN enforces
  uniqueness of domain names across the Internet. Each domain name becomes registered in a central database known as the WhoIS database. Domains are defined by their TLDs. TLDs are controlled by IANA in a root zone database, which is essentially a database of all available TLDs.

• 了解DNS的注册工作。域名是通过域名注册商在interNIC注册，是ICANN的一种服务。ICANN强制保持互联网上域名的一致性。每个域名被注册到一个WhoIS的数据库。域名在ICANN在root zone数据库中设置TLD。

• Remember the steps involved in DNS resolution. Your browser asks the resolving DNS
  server what the IP address is for amazon.com. The resolving server does not know the address, so it asks a root server the same question. There are 13 root servers around the world, and these are managed by ICANN. The root server replies that it does not know the answer to this, but it can give an address to a TLD server that knows about .com domain names. The resolving server then contacts the TLD server. The TLD server does not know the address of the domain name either, but it does know the address of the resolving name server. The resolving server then queries the resolving name server. The resolving name server contains the authoritative records and sends these to the resolving server, which then saves these records locally so it does not have to perform these steps again in the near future. The resolving name server returns this information to the user’s web browser, which also caches the information.

• 记得DNS解析的过程。浏览器请求DNS服务器amazon.com的IP地址是多少。解析服务器不知道IP地址，所以他咨询root server。ICANN管理的全世界的13个root server，他们来识别域名对应的域名，如果他识别不了，他将请求转发给TLD服务器，TLD服务器也不知道域名地址，但是他知道解析域名的服务器，这个解析服务查询解析域名的服务器，这个服务器包含官方的解析记录并返回。然后解析服务器在本地保存以规避后续再次请求解析。本次浏览器将此次解析也进行cache保存。

• Remember the different record types. DNS consists of the following different record
  types: A (address record), AAAA (IPv6 address record), CNAME (canonical name record or alias), MX (mail exchange record), NS (name server record), PTR (pointer record), SOA (start of authority record), SPF (sender policy framework), SRV (service locator), and TXT (text record). You should know the differences among each record type.

• 理解不同的record type。

• A：域名的IP地址；

• AAAA：IPV6的地址记录；

• CNAME：别名或者称作规范名称；

• MX：邮件服务器记录

• NS：name server

• PTR：通过IP地址解析域名；可以称作反向DNS解析；

• SOA：授权记录的开始，每个域名解析默认都有；

• SPF：防垃圾邮件的策略框架；

• SRV：服务资源记录，描述哪个计算机提供了哪些服务；

• txt：服务器的文本描述；

• Remember the different routing policies. With Amazon Route 53, you can have
  different routing policies. The simple routing policy is most commonly used when you have a single resource that performs a given function for your domain. Weighted routing is used
  when you want to route a percentage of your traffic to a particular resource or resources.
  Latency-based routing is used to route your traffic based on the lowest latency so that your users get the fastest response times. Failover routing is used for DR and to route your traffic from a primary resource to a standby resource. Geolocation routing is used to route your traffic based on your end user’s location.

• 理解不同的route 策略；

• simple策略：是最通过的路由策略，将你的单一资源映射到一个特定的功能函数上；

• weighted策略：当你想将一定百分比的流量导向一个特定的资源；

• latency-based策略：被用来将你的流量导向最低延迟的服务器；

• failvoer策略：是将你的容灾服务器提供到你的主服务，作为standby；

• Geolocation策略：被用来将你的流量基于终端用户的位置进行分发；