AWS学习笔记（十）：Route 53

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
• Ability to check the health of your resources
• The only AWS service which provides 100% availability SLA (Service Level Agreements 服务级协定)
• Why Route 53? 53 is a reference to the traditional DNS port
• $0.50 per month per hosted zone

Route 53 – Records

• 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 – 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 – Records TTL (Time To Live)

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 Record is always of type A/AAAA for AWS resources (IPv4 / IPv6)
• You can't set the TTL
• You cannot set an ALIAS record for an EC2 DNS name

Routing Policies - Simple

• 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

Route 53 – Health Checks

HTTP Health Checks are only for public resources

• Health Check => Automated DNS Failover:
  1. Health checks that monitor an endpoint (application, server, other AWS resource)
  2. Health checks that monitor other health checks (Calculated Health Checks)
  3. 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 – 30 sec (can set to 10 sec – 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

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