pdfbox

What it is#

Serverless multi-tenant PDF storage on AWS, written in Go and provisioned with Terraform, where file bytes never pass through the backend.

The API writes metadata to DynamoDB and hands the browser a short-lived S3 presigned URL; the browser then uploads or downloads directly against S3. Lambda handles kilobytes of JSON whether the user uploads 12 KB or 50 MB.

Architecture#

Lambda (Go) behind an API Gateway HTTP API, DynamoDB for metadata, S3 for objects, S3 notifications into SQS with a DLQ, IAM roles and JWT (HS256) for identity, all provisioned with Terraform.

The upload flow:

1. The client calls POST /files with filename, size and MIME type.
2. The API writes a pending record keyed by the JWT’s user_id and returns a presigned PUT URL, valid for 15 minutes, with Content-Type and the exact Content-Length in the signature.
3. The browser uploads straight to S3.
4. S3 emits s3:ObjectCreated:* to an SQS queue.
5. A worker Lambda checks the object’s real size against the record and the 50 MB ceiling, then marks the record uploaded, or rejected and deletes the object.

What I learned#

The README’s design decisions, in short:

• Presigned URLs instead of proxying. Proxying through Lambda would cap uploads at Lambda’s 6 MB request payload limit, well under the 50 MB the product allows.
• The confirmation comes from S3, not the client. The client can close the tab, lose connectivity or confirm without uploading anything; only S3 knows whether the object exists.
• Idempotency, because SQS is at-least-once. The worker treats a duplicate event as success, not as an error.
• Conditional writes instead of read-then-write. Every DynamoDB write carries a ConditionExpression, so the check is atomic with the write.
• Authorization is structural. The JWT’s user claim builds the partition key, so another user’s data is never in hand to be checked.
• No dual-write problem. The backend writes only to DynamoDB; S3 publishes the event atomically with the object write.

What’s next#

From the README’s “Not yet implemented” list:

• The reconciliation Lambda and its EventBridge Scheduler rule (cmd/event-bridge exists but is empty).
• The DynamoDB TTL that purges trashed records after a retention window.
• A restore-from-trash route.