Route 53 Flashcards
Route 53 is highly available, fully managed and Authoritative DNS - what does Authoritative mean here?
The customer can update the DNS records
What is Route 53 in the scope of DNS?
A Domain Registrar - allows the creation of domain names that are translated to IP addresses.
What type of information does each Route 53 record contain?
The information that allows you to route traffic for a domain
What specific information does each Route 53 record contain?
- 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 (the amount of time the record is cached at DNS Resolvers)
What record types does Route 53 support?
Must know - A, AAAA, CNAME, NS
Advanced - CAA, DS, MX, NAPTR, PTR, SOA, TXT, SPF, SRV
What is the purpose of record type A?
Maps a hostname to IPv4
What is the purpose of record type AAAA?
Maps a hostname to IPv6
What is the purpose of record type CNAME?
Maps a hostname to another hostname, where the target is a domain name that has an A or AAAA record
Give an example of where you would not be able to create a CNAME record
Can’t create a CNAME record for the top node of a DNS namespace (Zone Apex) - e.g., can’t create for example.com, but you can for www.example.com
What is the purpose of record type NS?
Name Servers for the Hosted Zone - these control how traffic is routed for a domain
What is a hosted zone?
A container for records that define how to route traffic to a domain and its subdomains
What is a public hosted zone?
Contains records that specify how to route traffic on the Internet (public domain names)
What is a private hosted zone?
Contain records that specify how you route traffic within one or more VPCs (private domain names)
How much does a hosted zone cost per month with AWS?
$0.50
TTL is mandatory for all DNS records except…
Alias records
Describe the basic DNS flow
- Web browser wants to access example.com
- Local DNS server queries the Root DNS server for the .com NS
- Local DNS server then queries the Top Level Domain (TLD) DNS server for the example.com NS
- Local DNS server then queries the Sub Level Domain (SLD) DNS server for the example.com IP address
What are the trade-offs of different record TTLs? Give a strategy for handling a record change.
High TTL (e.g., 24hr)
- Less traffic on Route 53
- Possibly outdated records
Low TTL (e.g. 60sec)
- More traffic on Route 53 so more expensive
- Records are outdated for less time
- Easy to change records
When wanting to change records, can decrease TTL then change the records so that Clients quickly pick up the change. After a certain amount of time, increase the TTL again (if you know the record will not be changing again soon)
What does the Record TTL do?
Tells the client how long to cache the DNS record (i.e., the resolved IP address)
State the difference between CNAME and Alias
CNAME:
- Points a hostname to any other hostname
- Only for non-root domain (e.g., application.example.com but not example.com)
Alias:
- Points a hostname to an AWS resource
- Works for root domain and non root domain
- Free
- Native health check
What type of record is an Alias?
A or AAAA for AWS records
Give a limitation of Alias records
You can’t set the TTL
What routing policies does Route 53 support?
Simple, Weighted, Failover, Latency based, Geolocation, Multi-Value Answer, Geoproxitimity (using Route 53 Traffic Flow Feature)
What is the difference between Route 53 routing and Load balancer routing?
Route 53 routing involves routing DNS queries (translating hostnames into endpoints).
Load balancer involves routing a request to an application on an instance.
Describe the Simple Routing Policy
Route traffic to a single resource - Route 53 will return one/many values (IP addresses) within a record, and if there are many values, the client will randomly choose one.
Give a limitation of the Simple Routing Policy
Can’t be associated with Health Checks.
Describe the Weighted Routing Policy
Control the % of requests that go to a specific resource.
What is a requirement when using a Weighted Routing Policy?
DNS records must have the same name and type
Can Weighted Routing Policy be associated with Health Checks?
Yes. Yes it can.
Give a use case of Weighted Routing Policy.
Load balancing between regions, testing new application versions.
How would you stop sending traffic to a resource using a Weighted Routing Policy?
Assign a weight of 0 to the record for that resource.
How would you send equal traffic to all resources using a Weighted Routing Policy?
Assign all records a weight of 0.
Describe Latency-based Routing Policy
Redirect to the resource that has the least latency close to us.
What is Latency based on in the Latency-based Routing Policy?
Based on traffic between users and the AWS regions
Can Latency Routing Policy be associated with Health Checks?
Yes - also has failover capacity
What type of HTTP resource can Route 53 Health Checks be assigned to?
Public resources
What can a Health Check monitor?
Can monitor an endpoint, other health checks or cloudwatch alarms.
How does a Health Checker monitor an endpoint?
- About 15 global health checkers will send a HTTP request to /health, looking for a 2xx or 3xx status code
What Endpoint Health Checker parameters can be specified?
- Set a threshold determining healthy vs unhealthy (default is 3)
- Set an interval for the health check (30 sec, 10 sec can be set at a higher cost).
What protocols does the Endpoint Health Checker support?
HTTP/S and TCP
Other than an HTTP response code, how else can you specify whether an Endpoint is deemed healthy?
Health Check can be setup to pass/fail based on the text in the first 5120 bytes of the response.
What is the %age threshold for a health checker to deem an endpoint ‘healthy’?
> 18% is healthy.
What is a requirement for using Route 53 Health Checkers?
Configure your router/firewall to allow incoming requests from Route 53 Health Checkers
Describe what a Calculated Health Check is
Combine the results of multiple Health Checks into a single Health Check.
What Calculated Health Checker parameters can be specified?
Number of Child Health Checks to be monitored - up to 256.
Specify how many of the health checks need to pass to make the parent pass.
Give a use case of a Calculated Health Check?
Perform maintenance to your website without causing all health checks to fail.
How to you perform Health Checks on Private resources?
Create a CloudWatch Metric and associate a CloudWatch Alarm, then create a Health Check that checks the alarm itself.
Why can you not perform Health Checks on private endpoints?
Route 53 Health Checkers are outside the VPC - cannot access private endpoints.
Describe the Failover Routing Policy
- Designate a Primary and Secondary EC2 instance (secondary if for disaster recovery)
- Mandatory Health check on primary, if this fails then traffic is routed to secondary backup instance.
Describe the Geolocation Routing Policy
- Routing is based on user location
- Specify by Continent, Country or US state (if any overlap, most precise location is chosen)
- Should create a ‘Default’ record (in case there is no match on location)
- Can be associated with Health checks
Give a use case for the Geolocation Routing Policy
- Website localization
- Restrict content distribution
- Load balancing
Describe the Geoproximity Routing Policy
- Route traffic to your resources based on the location of users and resources
- Can shift more traffic to resources based on a defined bias (more bias to a region means more traffic and vice versa)
With Geolocation Routing Policy, how can you specify the location?
- AWS resources are specified by region
- Non-AWS resources are specified by latitude and longitude
What does Geolocation Routing Policy require?
Route 53 Traffic Flow
What does a Traffic Flow Policy do?
- Acts as a configuration file for complex Routing decision trees
- Can be applied to different Route 53 Hosted Zones (different domain names)
What is Route 53 Traffic Flow?
A visual editor to manage complex routing decision trees.
Describe the Multi-Value Routing Policy
- Route traffic to multiple resources
- Route 53 will return multiple values/records (up to 8 healthy resources)
What is another way of describing the Multi-Value Routing Policy?
Client side load balancing
What is the difference between Multi-Value Routing Policy returning many values and Simple Routing Policy returning many values
Simple Routing Policy does not allow health checks - may return unhealthy records
How would you use a 3rd party Domain Registrar with Route 53 as the DNS Service?
- Register domain on 3rd party
- Create public Hosted Zone on Route 53
- Copy Name Servers (NS) across from Route 53 to 3rd party registrar
