Create a second CloudFront distribution that uses the second S3 bucket as a single origin. Create an origin group. Add both distributions to the origin group. Set the original distribution as the primary distribution. Set the new distribution as the secondary distribution. Create an Amazon Route 53 health check to monitor the health of the primary distribution and secondary distribution every second.

Create a new origin in the existing CloudFront distribution. Specify the second S3 bucket as the new origin. Create an origin group. Add the original origin as the primary origin. Add the new origin as the secondary origin. Set the origin response timeout value to 1. Set the origin connection attempts value to 1.

Create a new origin in the existing CloudFront distribution. Specify the second S3 bucket as the new origin. Create an origin group. Add the original origin as the primary origin. Add the new origin as the secondary origin. Update the default cache behavior to use the origin group. Set the origin connection timeout value to 1. Set the origin connection attempts value to 1.

Create a new origin in the existing CloudFront distribution. Specify the second S3 bucket as the new origin. Create an AWS Lambda function to monitor the health of the original origin. Program the Lambda function to update the CloudFront distribution and promote the secondary origin to primary if a health check fails. Create an Amazon EventBridge scheduled rule to invoke the Lambda function every second.