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route53.md

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Route 53

  • Route53 is a Managed DNS (Domain Name System)
  • DNS is a collection of rules and records which helps clients understand how to reach a server through its domain name
  • In AWS, the most common records are:
    • A: map a hostname to IPv4
    • AAAA: map a hostname tp IPv6
    • CNAME: map a hostname to another hostname
    • Alias: map a hostname to an AWS resource
  • Route 53 can use:
    • public domain names we own
    • private domain name that can be resolved by EC2 instances inside our VPCs
  • Route53 has advanced features such as:
    • Load balancing through DNS - also called client load balancing
    • Health checks
    • Routing policy: simple, failover, geolocation, latency, weighted, multi value
  • We pay $0.5 per month per hosted zone

DNS Records TTL (Time to Live)

  • TTL a is way for web browser adn clients to cache the response of the DNS query
  • Reason for caching is not to overload the DNS
  • The client will cache the DNS response for the duration of the TTL value (duration value is seconds)
  • High TTL (24 hours):
    • Less traffic for DNS
    • Possibility of outdated records
  • Low TTL (60 seconds):
    • More traffic on DNS
    • DNS records wont be outdated for longer periods which makes changing DNS records easier
  • TTL is mandatory for each DNS record!

CNAME Records vs Alias Records

  • AWS resources usually expose an AWS hostname
  • CNAME (Canonical Name record):
    • Points a domain name to any another domain name (example: app.mydomain.com => other.domain.com)
    • CNAME records work only for non root domains! (example of a non-root domain: something.rootdomain.com)
  • Alias records:
    • Point a hostname to an AWS resource (app.mydomain.com => something.amazonaws.com)
    • Alias records work for both root and non-root domain
    • They are free of charge
    • They can do health checks

Route53 Health Checks

  • If an instance is unhealthy, Route53 does not send traffic to it
  • An instance is unhealthy if if fails to respond to X (default 3) amount of requests in a row
  • It becomes healthy again if passes X (default 3) health checks in a row
  • Default health checks interval is 30s (Fast Health Checks: can be set to 10s - higher cost)
  • About 15 health checkers will check the end-point's health
  • Health check protocols: HTTP, TCP, HTTPS (no SSL verification)
  • Can be integrated with CloudWatch

Routing Policies

Simple Routing Policy

  • Used to redirect to a single source
  • We can not attach health checks to a simple routing policy
  • Simple routing policy can return multiple values to a client
  • If multiple values are returned the client can chose a random value

Weighted Routing Policy

  • Controls the percentage of the requests that goes to a specific end-point
  • Helpful to test a certain percentage of traffic on a new application version
  • Helpful to split traffic between two regions
  • Can be associated with health checks

Latency Routing Policy

  • Redirects to a server that has the least latency to the client
  • Mainly used when latency is a priority for the clients
  • Latency is evaluated in terms of user to designed AWS Region

Failover Routing Policy

  • Requires a primary record and a secondary record (disaster recovery)
  • If the primary record fails, traffic is routed to the secondary record
  • Requires a health check in order to work, failover is detected based on health checks

Geolocation Routing Policy

  • It is routing based on the user's location
  • We can specify where the traffic should be routed if the user is requesting from an IP that originates from a country
  • Requires a default policy (in case there is no match for a location)

Geoproximity Routing Policy

  • It is also routing based on the user's location
  • We can optionally choose to route more traffic or less to a given resource by specifying a value known as bias
  • To use geoproximity routing, we must use Route 53 traffic flow
  • We create geoproximity rules for our resources and specify one of the following values for each rule:
    • If we are using AWS resources, the AWS Region that you created the resource in
    • If we are using non-AWS resources, the latitude and longitude of the resource

Multi Value Routing Policy

  • Can be used when we need to route traffic to multiple resources and we want to associate Route53 health checks to the records
  • It will return up to 8 healthy records for each Multi Value query
  • It is not a substitute for Elastic Load Balancer!

Route 53 as a Registrar

  • A domain name registrar is an organization that manages the reservation of internet domain names. Some domain registrars are: GoDaddy, Google Domain and also Route 53
  • It is possible to use a third party domain registrar with AWS. In order to use a domain bought from the third party, we have to do the following:
    1. Create a hosted zone in Route53
    2. Update NS records on 3rd party website to use Route 53 name servers