In certain scenarios, you may need to override the default DNS resolution behavior in your AWS Lambda functions. This can be useful for various reasons, such as bypassing network restrictions, resolving domain names to specific IP addresses, or testing your application with different DNS configurations. Here’s how you can override DNS settings in an AWS Lambda Python function.

import socket
import dns.resolver
# Cache resolver object
resolver = dns.resolver.Resolver()
resolver.nameservers = ["", ""]
# Use constant for record
def lookup_dns_record(record):
        return socket.gethostbyname(record)
    except Exception as e:
        return {"status": "failure", "error": str(e)}

def lambda_handler(event):
    global resolver
    # Get IP before overriding resolver
    before_ip = lookup_dns_record(RECORD)
    # Override system resolver
    # Get IP after overriding
    after_ip = lookup_dns_record(RECORD)
    print(f"Before: {RECORD} = {before_ip}")
    print(f"After: {RECORD} = {after_ip}")
    return {
        "status": "success"

Creating a Lambda Layer

To use the dnspython library in your Lambda function, you need to create a Lambda layer. A Lambda layer is a ZIP archive that contains libraries or other dependencies that can be used by your Lambda functions. Follow these steps to create a Lambda layer:

  1. Install the dnspython library in a Python virtual environment.
mkdir python
python3 -m pip install dnspython boto3 -t python
  1. Create a ZIP archive containing the dnspython library and its dependencies.
zip -r python
  1. Upload the ZIP archive as a Lambda layer in the AWS Lambda console or using the AWS CLI.
aws lambda publish-layer-version \
    --layer-name dnspython-layer \
    --zip-file fileb:// \
    --compatible-runtimes python3.10

Once the layer is created, you can attach it to your Lambda function, allowing you to use the dnspython library and override the DNS settings.

aws lambda update-function-configuration \
    --function-name your-lambda-function-name \
    --layers arn:aws:lambda:your-region:your-account-id:layer:dnspython-layer:1

Why Override DNS Settings?

There are several reasons why you might want to override the default DNS resolution behavior in your Lambda functions:

  1. Bypassing Network Restrictions: Some networks or environments may have restrictions or filtering rules that prevent access to certain domains or IP addresses. By overriding DNS settings, you can bypass these restrictions and resolve domains to the desired IP addresses.
  2. Testing and Debugging: When testing or debugging your application, you may want to resolve domain names to specific IP addresses for testing purposes or to simulate different network conditions.
  3. Security and Privacy: In some cases, you may want to use specific DNS servers for security or privacy reasons, such as using DNS-over-HTTPS (DoH) or DNS-over-TLS (DoT) services.
  4. Geo-location and Load Balancing: By resolving domain names to different IP addresses based on geographic location or load balancing requirements, you can ensure that your application accesses the appropriate resources or services.

Additional Considerations

  • Performance Impact: Overriding the DNS resolver may introduce some overhead and potentially impact the performance of your Lambda function. Consider implementing caching mechanisms or other optimizations if necessary.
  • Security and Compliance: When overriding DNS settings, ensure that you are complying with any security policies or compliance requirements specific to your organization or application.
  • Maintenance and Updates: Keep in mind that the dnspython library and your Lambda function code may need to be updated periodically to address any security vulnerabilities or compatibility issues.

By following the steps outlined in this article, you can easily override DNS settings in your AWS Lambda Python functions, enabling you to customize the DNS resolution behavior according to your specific requirements.