Exporting Redis backups

When exporting backups of a Redis node or cluster to S3, you'll be greeted by a rather unhelpful permissions error saying AWS could not validate the user has permission to write to that bucket.

To fix the problem, you need to create an S3 bucket with ACLs enabled, and add a specific canonical ID to the ACLs.

More information is here: https://docs.aws.amazon.com/AmazonElastiCache/latest/red-ug/backups-exporting.html#backups-exporting-grant-access