Route 53 - TTL/CNAME vs Alias

Question 1

What does TTL stand for in DNS?

Answer 1

TTL stands for Time To Live, which defines how long a DNS record is cached by clients or resolvers.

Question 2

How does TTL work in DNS caching?

Answer 2

TTL instructs clients to cache a DNS response for a specified duration, reducing the need for repeated DNS queries within that period.

Question 3

What happens if a DNS record has a high TTL?

Answer 3

A high TTL (e.g., 24 hours) reduces DNS traffic but can lead to outdated records being cached for longer periods if changes are made.

Question 4

What are the implications of setting a low TTL?

Answer 4

A low TTL (e.g., 60 seconds) ensures records update faster but increases DNS traffic and costs.

Question 5

What strategy can be used when planning to change a DNS record?

Answer 5

Decrease the TTL in advance to ensure clients receive updates quickly, then make the change and later increase the TTL back to its original value.

Question 6

Is TTL mandatory for all DNS record types in Route 53?

Answer 6

Yes, TTL is mandatory for all records except Alias records.

Question 7

What happens if a client tries to access a cached DNS record after the TTL expires?

Answer 7

The client queries the DNS system again to retrieve the updated record.

Question 8

What command can you use to query a DNS record and observe its TTL?

Answer 8

The dig command can be used to query a DNS record and display its TTL.

Question 9

What is a practical use of nslookup in testing DNS records?

Answer 9

The nslookup command can verify that a DNS record resolves to the correct IP address.

Question 10

How does a change in a DNS record propagate with respect to TTL?

Answer 10

Changes take effect after the TTL of the cached records expires, prompting clients to fetch the updated record.

Question 11

What does a “120 seconds” TTL mean for a DNS record?

Answer 11

It means the record will be cached for 120 seconds before clients must query the DNS again for updates.

Question 12

What is the purpose of setting a TTL for DNS records?

Answer 12

TTL helps balance between reducing DNS traffic and ensuring records are up-to-date for clients.

Question 13

What is a CNAME record in DNS?

Answer 13

A CNAME record maps one domain name to another domain name. For example, app.mydomain.com can point to blabla.anything.com.

Question 14

Can CNAME records be used at the apex of a DNS zone?

Answer 14

No, CNAME records cannot be used at the zone apex (e.g., mydomain.com).

Question 15

What is an Alias record in AWS Route 53?

Answer 15

An Alias record maps a domain name to an AWS resource, such as an ELB, CloudFront distribution, or S3 website.

Question 16

Can Alias records be used at the apex of a DNS zone?

Answer 16

Yes, Alias records can be used at the zone apex (e.g., mydomain.com).

Question 17

What are the key benefits of using Alias records over CNAMEs in Route 53?

Answer 17

Alias records are free of charge, support root domains, and automatically update with changes to AWS resource IPs.

Question 18

Can Alias records be used to point to an EC2 DNS name?

Answer 18

No, Alias records cannot point to an EC2 DNS name.

Question 19

What types of AWS resources can Alias records point to?

Answer 19

Alias records can point to:

Elastic Load Balancers (ALB/CLB)
CloudFront distributions
API Gateway endpoints
Elastic Beanstalk environments
S3 websites
VPC interface endpoints
Global Accelerator
Route 53 records in the same hosted zone

Question 20

What is the difference between TTL management in CNAME and Alias records?

Answer 20

CNAME: TTL can be set manually.
Alias: TTL is managed automatically by Route 53.

Question 21

What happens if the IP of an AWS resource changes for an Alias record?

Answer 21

The Alias record automatically updates to reflect the new IP without requiring manual intervention.

Question 22

Why might you use an Alias record instead of a CNAME?

Answer 22

You might use an Alias record for root domain support, integration with AWS resources, cost savings, and automatic IP updates.

Question 23

How can you redirect a root domain (e.g., example.com) to an AWS resource?

Answer 23

Use an Alias record pointing to the AWS resource, such as an ALB or CloudFront distribution.