Implement a Route 53 failover routing policy with a health check to monitor the ALB's status and redirect to a failover S3 bucket endpoint.

Establish a second CloudFront distribution and S3 static website for the custom error page, configuring a Route 53 failover routing policy with an active-passive setup between the distributions.

Set up a CloudFront origin group with two origins: the ALB as the primary and an S3 bucket configured for static websites as the secondary. Enable origin failover in the CloudFront distribution and update the S3 static website to include the custom error page.

Develop a CloudFront function to check each HTTP response code from the ALB. Create an S3 static website and upload the custom error page for failover. Modify the function to retrieve and serve the error page from the S3 bucket.