Route 53

• Route 53 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 URLs.

• In AWS, the most common records are (will be on exam):
  • A: URL to IPv4
  • AAAA: URL to IPv6
  • CNAME: URL to URL
  • ALIAS: URL to AWS resource
• Route 53 can use:
  • Public domain names you own
  • Private domain names that can be resolved by your instances in your VPCs
• Route53 has advanced features such as:
  • Load balancing (through DNS - also called client load balancing)
  • Health checks (although limited…)
  • Routing policy: simple, failover, geolocation, geoproximity, latency, weighted
• Prefer Alias over CNAME for AWS resources (for performance reasons)

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  • Possibility of outdated records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  • DNS records wont be outdated for longer periods which makes changing DNS records easier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 go 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

Geo Location 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)

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!