This blog is a part of my journey “Embarking on the AWS Solution Architect Associate SAA-CO3 Certification Journey”

What is DNS?

• Domain Name System which translates the human friendly hostnames into the machine IP addresses.
• DNS is the backbone of the Internet
• DNS uses hierarchical naming structure

DNS Terminologies

• Domain Registrar : Amazon Route 53, GoDaddy
• DNS Records: A, AAAA, CNAME, NS
• Zone File: contains DNS records
• Name Server: resolves DNS queries (Authoritative or Non-Authoritative)
• Top Level Domain (TLD): .com, .us, .in, .gov, .org,
• Second Level Domain (SLD): amazon.com, google.com

Amazon Route 53

• A highly available, scalable, fully managed and Authoritative DNS
  • Authoritative = the customer (you) can update the DNS records
• Route 53 is also a Domain Registrar
• Has ability to check the health of your resources
• The only AWS service which provides 100% availability SLA
• Why Route 53? 53 is a reference to the traditional DNS port

Route 53 – Records

• How you want to route traffic for a domain.
• Each record contains:
  • Domain/subdomain Name – e.g., example.com
  • Record Type – e.g., A or AAAA
  • Value – e.g., 12.34.56.78
  • Routing Policy – how Route 53 responds to queries
  • TTL – amount of time the record cached at DNS Resolvers
• Route 53 supports the following DNS record types:
  • (must know)A /AAAA / CNAME / NS
  • (advanced)CAA/DS/MX/NAPTR/PTR/SOA/TXT/SPF/SRV

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 create for www.example.com
• NS – Name Servers for the Hosted Zone
  • Control how traffic is routed for a domain

Hosted Zones

• A 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) application1.mypublicdomain.com
• Private Hosted Zones – contain records that specify how you route traffic within one or more VPCs (private domain names) application1.company.internal
• You pay $0.50 per month per hosted zone

Records TTL (Time To Live)

• High TTL – e.g., 24 hr
  • Less traffic on Route 53
  • Possibly outdated records
• Low TTL – e.g., 60 sec.
  • 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 record

CNAME vs Alias

• AWS Resources (Load Balancer, CloudFront…) expose an AWS hostname: lb1-1234.us-east-2.elb.amazonaws.com and you want myapp.mydomain.com
• CNAME
  • Points a hostname to any other hostname. (app.mydomain.com => blabla.anything.com)
  • ONLY FOR NON ROOT DOMAIN (aka. something.mydomain.com)
• Alias
  • Points a hostname to an AWS Resource (app.mydomain.com => blabla.amazonaws.com
  • Works for ROOT DOMAIN and NON ROOT DOMAIN (aka mydomain.com)
  • Free of charge
  • Native health check

Alias Records

• Maps a hostname to an AWS resource
• An 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), e.g.: example.com
• Alias Record is always of type A/AAAA for AWS resources (IPv4 / IPv6)
• You can’t set the TTL
• Alias Records Targets
  • Elastic Load Balancers
  • CloudFront Distributions
  • API Gateway
    
  • Elastic Beanstalk environments
  • S3 Websites
  • VPC Interface Endpoints
  • Global Accelerator accelerator
  • Route 53 record in the same hosted zone
• You cannot set an ALIAS record for an EC2 DNS name

Routing Policies

• Define how Route 53 responds to DNS queries
• Don’t get confused by the word “Routing”
  • It’s not the same as Load balancer routing which routes the traffic
  • DNS does not route any traffic, it only responds to the DNS queries
• Route 53 Supports the following Routing Policies
  • Simple
  • Weighted
  • Failover
  • Latency based
  • Geolocation
  • Multi-Value Answer
  • Geoproximity

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

Routing Policies – Weighted

• Control the % of the requests that go to each specific resource
• Assign each record a relative weight:
  • 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 versions
• 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

Routing Policies – 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
• Germany users may be directed to the US (if that’s the lowest latency)
• Can be associated with Health Checks (has a failover capability)

Routing Policies – Failover

Routing Policies – Geolocation

• Different from Latency-based!
• This routing is based on user location
• Specify location by Continent, Country or by US State (if there’s overlapping, most precise location selected)
• Should create a “Default” record (in case there’s no match on location)
• Use cases: website localization, restrict content distribution, load balancing
• Can be associated with Health Checks

Routing Policies – Geoproximity

• 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:
  • To expand (1 to 99) – more traffic to the resource
  • To shrink (-1 to -99) – less traffic to the resource
• Resources can be:
  • AWS resources (specify AWS region)
  • Non-AWS resources (specify Latitude and Longitude)
• You must use Route 53 Traffic Flow to use this feature

Routing Policies – IP-based Routing

• Routing is based on clients’ IP addresses
• You provide a list of CIDRs for your clients and the corresponding endpoints/locations (user-IP-to-endpoint mappings)
• Use cases: Optimize performance, reduce network costs
• Example: route end users from a particular ISP to a specific endpoint

Routing Policies – Multi-Value

• Use when routing traffic to multiple resources
• Route 53 return multiple values/resources
• Can be associated with Health Checks (return only values for healthy resources)
• Up to 8 healthy records are returned for each Multi-Value query
• Multi-Value is not a substitute for having an ELB