You plan to use Amazon Redshift ML in a primary AWS account while the source data is in an S3 bucket in a secondary account. You need a pipeline in the primary account that accesses the secondary-account S3 bucket without requiring public IPv4 addresses. Which architecture meets these requirements?

The correct architecture uses an S3 gateway endpoint in the primary account to access S3 data in the secondary account. Gateway endpoints provide private connectivity to S3 from within a VPC without traversing the internet. Interface VPC endpoints for SageMaker and Redshift ensure private communication for these services. Updating the S3 bucket policy grants the necessary cross-account access to the primary account's IAM principals. The other options are less suitable: VPC peering would allow network connectivity but doesn't inherently provide private access to S3 across accounts without additional configuration, and removing 0.0.0.0/0 routes could break other necessary internet access. AWS Direct Connect and Transit Gateway are for establishing private network connections between on-premises networks and AWS, or between multiple VPCs, but are overkill and not the most direct solution for S3 access between accounts. Site-to-Site VPN is primarily for connecting on-premises networks to AWS VPCs securely over the internet, not for inter-account S3 access within AWS.