Storing tenant IDs, leases and referencing packs is easy until someone asks who actually read them. Five failure families in property SaaS document storage, with the IAM policies, presigned URL mechanics, upload controls and deletion patterns that close each one.
A missing tenant filter doesn't throw an error, it returns a 200 with too many rows. This is how to build a multi-tenant workshop management platform on AWS where the isolation boundary sits below your application code: STS session tags feeding IAM conditions, DynamoDB leading keys, scoped S3 prefixes, forced PostgreSQL row-level security, and a control plane that verifies each new tenant is fenced before anyone logs in.