# AWS Certified Solutions Architect - Associate (DNS)
###### tags: `AWS`

### DNS
- SOA(Start Of Authority)
- The name of the server that supplied the data for the zone
- The administrator of the zone
- The current version of the data file
- The default number of seconds for the TTL file on resource records
- NS(Name Server Records)
They are used by Top Level Domain servers to direct traffic to the Content DNS server which contains the authoritative DNS records.
- A (Address)
The A record is used by a computer to traslate the name of the domain to an IP address.
- TTL
The length that DNS record is cached on either the Resolving Server or the users own local PC is equal to the value the "Time To Live"(TTL) in seconds.
The lower the time to live, the faster changes to DNS records take to propagate throughout the internet.
- CName (Canonical Name)
CName can be used to resolve one domain name to another.
- Alias Records
Alias records are used to map resource record sets in your hosted zone to Elastic Load Balancers, CloudFronts distributions, or S3 buckets that are configure.

**Difference:** A CNAME can't be used for naked domain names(zone apex record.) You can't have a CNAME for http://acloud.guru

Tips:
- ELBs don't have pre-defined IPv4 addresses; you resolve to them using a DNS name.
- Understand the difference between an Alias Record and a CNAME.
- Given the choice, always choose an Alias Record over a CNAME.
- Common DNS Types
- SOA
- NS
- A
- CNAMES
- MX
- PTR(Reverse A types)

Tips:
- You can buy domain names directly with AWS
- It can take up to 3 days to register depending on the circumstances

#### Routing policies
- Simple Routing
Can only have one record with multiple IP addresses.(In a records) If you specify multiple values in a record, Route53 returns all values to the user in a random order

- Weighted Routing
Allows you split your traffic based on different weights assigned.
> ### Health checks
> - You can set health checks on individual record sets
> - If a record set fails a health chcek it will be removed from Route53 until it passes the health check.
> - You can set SNS notification to alert you if a health check is failed
- Latency-based Routing
Allows you to route your traffic based on the lowest network latency for your end user.
- Failover Routing
Failover routing policies are used when you want to create an active/passive set up. For example, you may want your primary site to be in EU-WEST-2 and your secondary DR site in AP-SOUTHEAST-2
- Geolocation Routing(language)
Geolocation routing lets you choose where your traffic will be sent based on the geographic location of your users.
- Geoproximity Routing (Traffic Flow only)
Geoproximity Routing lets Route53 route traffic to your resources based on the geographic location of your users and your resources.
**To use geoproximity routing, you must use Route 53 traffic flow.**
- Multivalue Answer Routing
Multivalue answer routing lets you configure Amazon Route 53 to return multiple values, such as IP servers, in response to DNS queries.
**This is similar to simple routing however it allows you to put health checks on each record set**