502 Error. The request could not be satisfied.

I have a production cloudfront setup which serves images and it was working until yesterday. Suddenly today I get the following error.

502 ERROR

The request could not be satisfied.

CloudFront attempted to establish a connection with the origin, but either the attempt failed or the origin closed the connection. We can't connect to the server for this app or website at this time. There might be too much traffic or a configuration error. Try again later, or contact the app or website owner. 
If you provide content to customers through CloudFront, you can find steps to troubleshoot and help prevent this error by reviewing the CloudFront documentation. 
Generated by cloudfront (CloudFront)
Request ID: ....

I didn't make any changes and not sure why suddenly this happened. Puzzled.

FYI, My origin is set to HTTP only. This is production server and wanted to resolve it asap. Urgent please.