Below are some of the s3 limitations when using KMS
1. If you are using SSE-KMS to encrypt your objects in S3, you must keep in mind the KMS limits
2. When you upload a file, you will call GenerateDataKey in the KMS API.
3. When you download a file, you will call Decrypt in the KMS API.
4. Uploading/downloading will count towards the KMS quota.
5. Currently, you cannot request a quota increase for KMS.
6. Region-specific, however, it's either 5,500 10,000, or 30,000 requests per second.