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Sangwoo Lee
Sangwoo Lee

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[AWS] 7. AWS Route 53, DNS (Domain Name System), Routing Policies

#networking #aws #beginners #devops

What is DNS?

  • Domain Name System which translates the human friendly hostnames into the machine IP addresses
  • www.google.com → 172.217.18.36
  • DNS is the backbone of the Internet
  • DNS uses hierarchical naming structure (ex. .com, example.com, www.example.com, api.example.com)

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, ...

How DNS Works

Amazon Route 53

  • A high available, scalable, fully managed and Authoritative DNS
    • Authoritative = the customer (you) can update the DNS records
  • Route 53 is also a Domain Registrar
  • 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

Route 53 - 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

Route 53 - 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) ex) application1.mypublicdomain.com
  • Private Hosted Zones - contain records that specify how you route traffic within one or more VPCs (private domain names) ex) application1.company.internal
  • You pay $0.50 per month per hosted zone

Route 53 - Public vs Private Hosted Zones

Route 53 - Records TTL (Time To Live)

  • High TTL - e.g., 24hr
    • Less traffic on Route 53
    • Possibly outdated records
  • Low TTL - e.g., 60sec
    • 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:
    • lb-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)
  • Alisa:
    • 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

Route 53 - Alias Records

  • Maps a hostname to an AWS resource
  • An extension to DNS functionally
  • 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

Route 53 - 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

Route 53 - 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
    • (1) Simple
    • (2) Weighted
    • (3) Latency-based
    • (4) Failover (Active-Passive)
    • (5) Geolocation
    • (6) Geoproximity (using Route 53 Traffic Flow feature)
    • (7) Multi-Value Answer

(1) 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

(2) Routing Policies - Weighted

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

  • 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

(3) 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)

Route 53 - Health Checks

  • HTTP Health Checks are only for public resources
  • Health Check → Automated DNS Failover:
    • Health checks that monitor an endpoint (application, server, other AWS resource)
    • Health checks that monitor other health checks (Calculated Health Checks)
    • Health checks that monitor CloudWatch Alarms (full control !) - e.g., throttles of DynamoDB, alarms on RDS, custom metrics,... (helpful for private resources)
  • Health Checks are integrated with CW metrics

Health Checks - Monitor an Endpoint

  • About 15 global health checkers will check the endpoint health
    • Healthy/Unhealthy Threshold - 3 (default)
    • Interval - 30sec (can set to 10sec - higher cost)
    • Supported protocol: HTTP, HTTPS and TCP
    • If > 18% of health checkers report the endpoint is healthy, Route 53 considers it Healthy. Otherwise, it's Unhealthy
    • Ability to choose which locations you want Route 53 to use
  • Health Checks pass only when the endpoint responds with the 2xx and 3xx status codes
  • Health Checks can be setup to pass / fail based on the text in the first 5120 bytes of the response
  • Configure you router / firewall to allow incoming requests from Route 53 Health Checkers

Route 53 - Calculated Health Checks

  • Combine the results of multiple Health Checks into a single Health Check
  • You can use OR, AND or NOT
  • Can monitor up to 256 Child Health Checks
  • Specify how many of the health checks need to pass to make the parent pass
  • Usage: perform maintenance to your website without causing all health checks to fail

Health Checks - Private Hosted Zones

  • Route 53 health checkers are outside the VPC
  • They can't access private endpoints (private VPC or on-premises resource)
  • You can create a CloudWatch Metric and associate a CloudWatch Alarm, then create a Health Check that checks the alarm itself

(4) Routing Policies - Failover (Active-Passive)

(5) 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

(6) 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 (advanced) to use this feature

Geoproximity Routing Policy

Geoproximity Routing Policy Higher bias in us-east-1

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 (Elastic Load Balancer)

Domain Registrar vs DNS Service

  • You buy or register your domain name with a Domain Registrar typically by paying annual charges (e.g., GoDaddy, Amazon Registrar Inc., ..)
  • 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
  • Example: purchase the domain from GoDaddy and use Route 53 to manage your DNS records

GoDaddy as Registrar & Route 53 as DNS Service

3rd Party Registrar with Amazon Route 53

  • If you buy your domain on a 3rd party registrar, you can still use Route 53 as the DNS Service provider
  1. Create a Hosted Zone in Route 53
  2. Update NS Records on 3rd party website to use Route 53 Name Servers
  • Domain Registrar != DNS Service
  • But every Domain Registrar usually comes with some DNS features

Route 53 - Hybrid DNS

  • By Default, Route 53 Resolver automatically answers DNS queries for:

    • Local domain names for EC2 instances
    • Records in Private Hosted Zones
    • Records in public Name Servers

  • Hybrid DNS - resolving DNS queries between VPC (Route 53 Resolver) and your networks (other DNS Resolvers)

  • Networks can be:

    • VPC itself / Peered VPC
    • On-premises Network (connected through Direct Connect or AWS VPN)

Route 53 - Resolver Endpoints

  • Inbound Endpoint
    • allows your DNS Resolvers to resolve domain names for AWS resources (e.g., EC2 instances) and records in Private Hosted Zones

  • Outbound Endpoint
    • Route 53 Resolver forwards DNS queries to your DNS Resolvers

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