Short answer: put the avatar or training artifact behind a private object key, validate it before upload, attach metadata with a second write, and save that key in your database. Choose the storage layer by large-file behavior and retention semantics, not by whether its SDK has the nicest first five minutes.

Option Large-file path Metadata and retention fit Best boundary

Amazon S3 Multipart uploads and a mature object API Strong lifecycle controls; versioning and object lock are available configurations Teams that need the deepest AWS integration

Cloudflare R2 S3-compatible object API Useful when the rest of the edge stack is already Cloudflare; verify the retention and delivery controls you need Edge-heavy applications

MinIO S3-compatible API under your control Policy and durability depend on the deployment you operate Private infrastructure and on-prem requirements

Infrai storage REST object writes, with a separate metadata route Private objects and lifecycle policy; no public-read ACL, versioning, or…