DNS (for example, conditional forwarding, hosted zones, resolvers)

What is DNS conditional forwarding, and when would you use it in an AWS environment?

DNS conditional forwarding is a configuration that allows DNS queries for specific domains to be forwarded to a designated DNS server, instead of using the default DNS resolution path. In an AWS environment, you would use it when you want to resolve domain names that are internal to a company or when integrating with on-premises DNS servers. This is useful for hybrid cloud scenarios where resources are spread across AWS and on-premises data centers and specific name resolution is required for internal domains.

Can you explain what a DNS resolver is, and how it functions within a network?

A DNS resolver is a server within a network that receives DNS queries from clients and takes the necessary steps to resolve the names to IP addresses. It functions as an intermediary that queries other DNS servers to fetch the required DNS records and then returns the answers to the clients. The resolver handles caching of DNS responses, reducing the time needed for subsequent queries of the same domain names.

What are hosted zones in Amazon Route 53, and what are the two types of hosted zones?

Hosted zones in Amazon Route 53 are containers for DNS records for domains. There are two types of hosted zones: Public Hosted Zones, which are used to manage DNS records for domains accessible over the internet, and Private Hosted Zones, which are used for managing DNS records for a domain within one or more Amazon VPCs, making them accessible only within those VPCs.

How does Amazon Route 53 handle DNS failover, and what mechanisms are in place to support high availability?

Amazon Route 53 can route traffic to multiple resources and can monitor the health of those resources. If a primary resource becomes unavailable, Route 53 can automatically route traffic to a healthy secondary resource. It uses health checks and DNS failover to support high availability, redirecting users to alternate locations in case of an outage or a drop in the performance of the primary site.

What is the difference between Alias and CNAME records in Route 53, and when would you use each?

An Alias record is a Route 53-specific DNS record type that lets you map one DNS name to another ‘target’ DNS name while also providing Route 53’s native health checking. Unlike CNAME records, Alias records can be used for naked domain names (e.g., example.com) and are also used for AWS resources that have dynamic IP addresses. In contrast, CNAME records can only be used for subdomains and map a DNS name to any other DNS name, not necessarily an AWS resource. You would use an Alias record for AWS resources and root domain names, while CNAMEs are typically used for non-root domain mapping to external DNS names.

In AWS, what are some strategies to ensure low-latency DNS responses for a global user base?

To ensure low-latency DNS responses for a global user base in AWS, strategies include:
– Using Amazon Route 53’s global network of DNS servers to leverage the Anycast routing methodology.
– Implementing Route 53 latency-based routing to direct users to the AWS endpoint that provides the lowest possible latency.
– Configuring Geo DNS to route users to the nearest resource based on their geographic location.
– Utilizing a Content Delivery Network (CDN) like Amazon CloudFront along with Route 53 to distribute content closer to users and reduce DNS query latency.

How can you secure DNS queries between your VPC and on-premises networks in AWS?

To secure DNS queries between your VPC and on-premises networks in AWS, you can use the following measures:
– Setting up a VPN or AWS Direct Connect to create a secure connection between the networks.
– Running your own DNS servers on EC2 instances within your VPC and implementing DNS query encryption using protocols such as DNS over HTTPS (DoH) or DNS over TLS (DoT).
– Configuring Route 53 Resolver rules for conditional DNS forwarding to ensure that only certain queries are forwarded to on-premises DNS servers while maintaining strict access control.

What role does TTL (Time to Live) play in DNS, and how would you determine an optimal TTL value for a DNS record in AWS?

TTL (Time to Live) is a DNS setting that specifies the duration in seconds that a DNS record is cached by DNS resolvers and browsers before a new query is sent to the DNS server for updated information. The optimal TTL value for a DNS record in AWS depends on how frequently the record is updated or anticipated to be updated. A lower TTL is appropriate for resources with frequent changes, providing quick updates at the cost of increased DNS queries. For stable resources, a higher TTL value reduces the load on DNS servers and can improve DNS response times.

Can you explain the purpose and functionalities of Amazon Route 53 Resolver?

Amazon Route 53 Resolver serves as a regional DNS service for Amazon VPC that provides a scalable and highly available DNS service. It enables the automatic resolution of DNS queries both from AWS resources to the internet and from the internet to AWS resources. Route 53 Resolver also supports custom DNS queries routing, conditional DNS forwarding, and private DNS for AWS resources.

Describe a scenario in which you would set up a DNS failover to a secondary region in AWS.

You would set up DNS failover to a secondary region in AWS in case of regional outages or to enhance your application’s disaster recovery strategy. For instance, if you operate a mission-critical application, you can configure health checks in Route 53 to monitor the endpoints in the primary region. If the primary region becomes unavailable or fails the health checks, Route 53 will automatically reroute traffic to a standby environment in a secondary region to maintain availability.

What are the different routing policies available in Amazon Route 53, and how would you choose the appropriate one for a given use case?

The different routing policies available in Amazon Route 53 include Simple, Weighted, Latency, Failover, Geolocation, Geoproximity, and Multivalue answer policies. The choice of a routing policy depends on the use case:
– Simple: For a single resource that performs a given function for your domain.
– Weighted: To route traffic to multiple resources in proportions that you specify.
– Latency: To route traffic based on the lowest network latency for your end user.
– Failover: To configure active-passive failover.
– Geolocation: To route traffic based on the location of your users.
– Geoproximity: To route traffic based on geographic location and optional bias.
– Multivalue answer: To respond to DNS queries with up to eight healthy records selected at random.

How can you migrate a DNS domain to Amazon Route 53 without incurring downtime?

To migrate a DNS domain to Amazon Route 53 without incurring downtime:
– Start by creating the same DNS records in a new hosted zone in Route 53, making sure they match the existing records with your current DNS provider.
– Reduce the TTL for the DNS records at your current provider to minimize the caching period leading up to the migration.
– After confirming that the records are set up correctly in Route 53, update the domain’s NS records with your domain registrar to point to the Amazon Route 53 name servers.
– Monitor traffic to ensure that it starts resolving through Route 53, and after the TTL has expired, it’s safe to decommission the old DNS configuration.