In our multi-tenant e-commerce application we handled it like this: * Metadata for each file is stored in the database * The application accesses files throug

In our multi-tenant e-commerce application we handled it like this: * Metadata for each file is stored in the database * The application accesses files through an abstraction based on that metadata, and doesn't care if the actual file is stored in S3 or the database * File types which are small and few, are stored in the database. For example letterheads, logos, terms-and-conditions. (a few gigabytes total) * File types which are big (e.g. CSV-reports) or many (e.g. invoice-PDFs) are stored in S3 (several terabytes total) * Development and test systems often use the database for everything and don't have an associated S3 bucket. * Most of the application remains usable without S3 (access to invoice PDFs and CSV-reports is not critical) In our case the DB was Mongo, but I expect Postgres to work the same. We actually stored all files in the database originally, and only migrated after it reached several terabytes. It worked perfectly fine, but was rather expensive. So next time I'd go for S3 for the start.