Section 10 - Route 53

DNS
- Domain Name System which translates the human friendly hostnames into the machine IP address
- Uses hierarchical naming structure
- Domain Registrar: Amazon Route 53, GoDaddy
- DNS Records: A, AAAA, CNAME
- Zone file: contains DNS records
- Name Server: resolves DNS queries (Authoritative or Non-Authoritative)
- Top Level Domain (TLD): .com, .us, .org
- Second Level Domain (SLD): amazon.com, google.com
Amazon Route 53
- Highly available, scalable, fully managed and Authoritative DNS
- Authoritative = the customer (you) can update the DNS records
- Route 53 is a Domain Registrar
- Ability to check the health of your resources
- Only AWS service which provides 100% availability SLA
- Records
- Define how you want to route traffic for a domain
- Each record contains:
  - Domain/subdomain Name
  - Record Type
  - Value
  - Routing Policy
- Supports the following DNS record types:
  - A - maps a hostname to IPv4
  - AAAA - maps a hostname to IPv6
  - CNAME - maps a hostname to another hostname
  - The target is a domain name which must have an A or AAAA record
  - Can't create a CNAME record for the top node of a DNS namespace (Zone Apex)
  - Example: you can't create for example.com, but you can for www.example.com
  - CNAME vs Alias
    - CNAME
    - Points a hostname to any other hostname
    - Only for non root domain
    - Alias
    - Points a hostname to an AWS Resource
    - Works for Root domain and non root domain
    - free of charge
    - native health checks
    - Extension to DNS functionality
    - Automatically recognizes changes in the resource's IP addresses
    - Unlike CNAME, it can be used for the top node of a DNS namespace (Zone Apex)
    - Alias record is always of type A/AAAA for AWS resources
    - You can't set the TTL
    - Records Targets
      - ELB, CloudFront Distributions, API Gateway, Elastic Beanstalk environments, S3 Websites
      - Cannot set an ALIAS record for an EC2 DNS name
  - NS - Name Servers for the Hosted Zone
  - control how traffic is routed for a domain
- TTL (Time to Live)
  - High TTL - 24hr
  - Less traffic on route 53
  - Possibly outdated records
  - Low TTL - 60s
  - More traffic on Route 53
  - Records are outdated for less time
  - Easy to change records
  - Except for Alias records, TTL is mandatory for each DNS
- Hosted Zones
- Container for records that define how to route traffic to a domain and its subdomains
- Public Hosted Zones - contains records that specify how to route traffic on the internet (public domain names)
- Private Hosted Zones - contain records that specify how you route traffic within one or more VPCs (private domain names)
- Routing Policies
- Define how Route 53 responds to DNS queries
- DNS does not route any traffic, it only responds to the DNS queries
- Supports the following routing policies
  - Simple
  - Typically route traffic to a single resource
  - can specify multiple values in the same record
  - If multiple values are returned, a random one is chosen by the client
  - When Alias enabled, specify only one AWS resource
  - Can't be associated with Health Checks
  - Weighted
  - Control the % of the requests that go to each specific resource
  - Assign each record a relative weight:
    - traffic (%) = Weight for a specific record/Sum of all the weights for all records
    - Weights don't need to sum up to 100
  - DNS records must have the same name and type
  - Can be associated with Health Checks
  - Use Cases: load balancing between regions, testing new application version
  - Assign a weight of 0 to a record to stop sending traffic to a resource
  - If all records have weight of 0, then all records will be returned equally
  - Failover
  - Latency based
  - Redirect to the resource that has the least latency close to us
  - Super helpful when latency for users is a priority
  - Latency is based on traffic between users and AWS regions
  - Can be associated with Health Checks (has a failover capability)
    - HTTP Health Checks are only for public resources
    - Automated DNS Failover:
    - Health checks that monitor an endpoint
      - about 15 global health checkers will check the endpoint health
    - Health checks that monitor other health checks
    - Health checks that monitor cloudwatch alarms
    - Integrated with CW metrics
  - Geolocation
  - Routing based on user loaction
  - Specify location by Continent, Country or by US State
  - Should create a "Default" record
  - Use cases: website localizations, restrict content distributions, load balancing
  - Associated with health checks
  - Multi-Value Answer
  - Geoproximity (Route 53 Traffic Flow feature)
  - Route traffic to your resources based on the geographic location of users and resources
  - Ability to shift more traffic to resources based on the defined bias
  - To change the size of the geographic region, specify bias values
  - Must use Route 53 traffic flow to use this feature
- Traffic Flow
- Simplify the process of creating and maintaining records in large and complex configs
- Visual editor to manage complex routing decision trees
- Configurations can be saved as Traffic Flow Policy
  - can be applied to different route 53 hosted zones
  - supports versioning
- Multi-value
- Use when routing traffic to multiple resources
- Route 53 return multiple values/resources
- Can be associated with Health Check (return only values for healthy resources)
- Up to 8 healthy records are returned for each Multi-Value query
- Mult-Value is not a substitute for having an ELB
- Domain Registar vs DNS Service
- You buy or register your domain name with a Domain Registrar typically by paying annual charges
- The Domain Registrar usually provides you with a DNS service to manage your DNS records
- But you can use another DNS service to manage your DNS records
  - Ex: Purchase the domain from GoDaddy and use Route 53 to manage your DNS records