What DNS Server Does EC2 Use?
When working with Amazon Web Services (AWS), specifically the Elastic Compute Cloud (EC2) service, it’s important to understand the Domain Name System (DNS) and how it relates to your EC2 instances. The DNS is responsible for translating domain names into IP addresses, allowing users to access websites and services using human-readable names.
The Default DNS Configuration
By default, EC2 instances use the Amazon-provided DNS resolver to perform DNS lookups. This resolver is available on every EC2 instance and is automatically configured when an instance is launched. It simplifies the process of resolving domain names by eliminating the need for manual configuration.
The Amazon-provided resolver uses a combination of local caching and recursive DNS queries to provide efficient and reliable resolution of domain names. It caches responses locally, reducing the need for repeated queries to external DNS servers, which improves performance.
How Does it Work?
When an application running on an EC2 instance makes a DNS query, the operating system forwards the request to the local resolver. The local resolver checks its cache first to see if it has a recent response for that particular domain name. If it does, it returns the cached response immediately.
If there’s no cached response available, the local resolver contacts one of AWS’s global network of recursive DNS resolvers. These resolvers are highly available and distributed across multiple regions worldwide. They are designed to handle a significant volume of requests efficiently.
The AWS recursive resolvers start by checking their own cache for a response. If they have a valid cached entry, they return it immediately to the local resolver on your EC2 instance.
If no cached entry is found, the AWS recursive resolver then performs iterative resolution starting from the root DNS servers. It sends queries to authoritative DNS servers responsible for the requested domain, following the chain until it obtains a response.
Customizing DNS Resolution
In some cases, you may need to customize the DNS resolution for your EC2 instances. For example, you might want to use your own DNS server or configure specific DNS settings for your applications.
To achieve this, AWS provides multiple options:
- Private Hosted Zones: You can create private hosted zones in Amazon Route 53 and associate them with your Amazon VPCs. This allows you to have complete control over the DNS resolution for your EC2 instances within a specific VPC.
- Elastic IP Addresses: If you assign an Elastic IP address to an EC2 instance, you can create a corresponding PTR (reverse DNS) record in the appropriate public DNS zone. This allows reverse DNS lookups to resolve back to your EC2 instance.
- Custom DHCP Options Sets: By creating a custom DHCP options set and associating it with your VPC, you can specify custom domain names and DNS servers for use by your EC2 instances.
The default DNS configuration used by EC2 instances relies on the Amazon-provided resolver. This resolver handles all necessary lookups and caching, ensuring efficient and reliable resolution of domain names. However, AWS also provides options for customizing DNS resolution based on specific requirements or preferences.
By understanding how the default DNS configuration works and being aware of available customization options, you can effectively manage and control the DNS resolution process for your EC2 instances in AWS.