Serving Private Files from Backblaze B2 in FastAPI

Serving Private Files from Backblaze B2 in FastAPI

I recently needed to serve private files (like PDFs and images) from my FastAPI backend, but I didn’t want to use AWS S3. Instead, I went with Backblaze B2—a cost-effective and S3-compatible object storage service.

In this post, I’ll walk you through how I used B2's private buckets and generated secure download links that FastAPI could serve dynamically.

🎯 The Goal

• Store files in a private B2 bucket
• Use FastAPI to securely serve/download those files
• Prevent direct access to the bucket (no public URLs)
• Avoid caching or temporary local storage

Setting Up B2

1. Create a B2 bucket.
2. Set the bucket to private.
3. Create an Application Key with appropriate permissions.

Connecting to B2 from Python

I used the official b2sdk to authenticate and fetch files: