These notes were written while working through the A Cloud Guru AWS Certified Solutions Architect - Associate online course. These notes are partly from the videos, and also from various other online sources. Primarily, they’re notes for me, but you might find them useful too.

Since the AWS platform is changing so quickly, it’s possible that some of these notes may be out of date, so please take that into consideration if you are reading them.

Please let me know in the comments below if you have any corrections or updates which you’d like me to add.

This post was last updated in March, 2019.

Route 53 (AWS’s DNS service)

Route 53 FAQ

Route 53 is named after the fact that DNS is on port 53

There is a limit of 50 domain names on Route 53 - this can be extended by contacting AWS support


  • CNAME (Canonical Name) can be used to resolve one domain to another
  • A Record (Address Record) for resolving a domain name to an IP address
  • Alias records are an AWS / Route 53 specific term, similar to CNAME with the key distinction that CNAMEs can’t be used on the zone apex (root domain i.e. cnames could be used against, but not against - for this you’d need to use either an A Record or Alias record)

Tip for the exam: if you’re given the option to choose between CNAME and Alias record, choose the Alias record.

ELBs and Route 53

ELBs operate on domain names only, and never have fixed IPv4 or IPv6 addresses. This means that it’s not possible to use an A Record to resolve to an ELB. You must use an Alias record; Alias records were created for this purpose.

Routing Polcies

  • Simple Routing
    • Map a single resource to another, i.e. the web server or ELB which serves content for
  • Failover
    • If you have multiple resources that perform the same function, you can configure DNS failover so that Route 53 will route your traffic from an unhealthy resource to a healthy resource. For example, if your EC2 instance becomes unhealthy, you could:
      • Failover to a healthy EC2 instance, or…
      • Failover to a static website hosted in an S3 bucket.
    • Make sure you have a healthcheck defined for the failover
    • For DR (disaster recovery)
    • When you want to configure active-passive failover
      • Primary is “active”, secondary is “passive”/DR
  • Geoproximity
    • For routing traffic based on the location of your resources
  • Latency Based Routing
    • Map one domain to one or more domains
    • Route traffic based on latency. i.e. if your ping to eu-west-2 is 300ms and the ping to ap-southeast-2 is 54ms, Latency Based Routing rules can be set to direct traffic to the lower latency region, ap-southeast-2
  • Multivalue
    • For returning multiple values such as IP addresses for healthy resources
  • Weighted Routing
    • Map one domain to one or more domains
    • i.e. direct 20% of traffic to an ELB in us-east-1, and 80% of traffic to an ELB in us-west-1
    • Good for A/B testing where you want to test a different website for a certain proporiton of your users
    • The weights are relative to each other, so they can be arbitrary values, not necessarily adding up to 100

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