If you have 2 AWS accounts and you want to copy the content from a S3 bucket from account A to account B, rather than downloading contents from 1 bucket A and uploading them to another bucket B, AWS CLI can help you with the task. Here are the steps you can do.

1. Open the Bucket Policy in account A add the following policy
   {
   “Version”: “2012-10-17”,
   “Statement”: [
   {
   “Sid”: “DelegateS3Access”,
   “Effect”: “Allow”,
   “Principal”: {“AWS”: “222222222222”}, //new account id
   “Action”: [“s3:ListBucket”,”s3:GetObject”], //this is the minimun privilege
   “Resource”: [
   “arn:aws:s3:::sourcebucket/*”,  // the source Bucket arn
   “arn:aws:s3:::sourcebucket”
   ]
   }
   ]
   }

2. Login to the account B with user key and run the following command

aws s3 sync s3://fromBucket/fromFolder s3://toBucket/toFolder

3. If you need a batch job to sync the content, then you can create a lambda and triggered by cloudwatch event to execute the cli command.

Happy days!