how to block a bot from causing high data downloads

Hello
The robots.txt file is an agreement which is not mandatory so it may help but it does not stop Yandex from keep doing it.
You can create a bucket policy to denie access to an IP address or IP address range.

here is an example
https://aws.amazon.com/premiumsupport/knowledge-center/block-s3-traffic-vpc-ip/

hope this helps
Rt

Thank you so much.
However, the example you give is for blocking all access and giving permission to specific IP addresses. I wish to do the opposite - to give public access, but block specific IP addresses.

Is there JSON code you know of which does this please?
thanks again

Hello
Sorry, this link should have a bit more info.

https://docs.aws.amazon.com/AmazonS3/latest/dev/example-bucket-policies.html#example-bucket-policies-use-case-3

a little modification to the other example and you have it.

{
  "Version": "2012-10-17",
  "Id": "S3PolicyId1",
  "Statement": [
    {
      "Sid": "IPAllow",
      "Effect": "Deny",
      "Principal": "*",
      "Action": "s3:*",
      "Resource": "arn:aws:s3:::examplebucket/*",
      "Condition": {
         "IpAddress": {"aws:SourceIp": "54.240.143.24/32"}
      } 
    } 
  ]
}

RT

Thank you so much - have it sorted. Really appreciate your time.