Migrating from S3 to UploadBird: A Complete Guide

The idea of moving off S3 can feel like pulling a thread on your whole stack. It doesn't have to. With the right plan you can shift to UploadBird without downtime, keep your URLs stable, and end up with a simpler pipeline. Here's the migration playbook we run with teams that want less AWS wrangling and more shipping.

Step 1: Map the surface area

Inventory what's in S3: buckets, prefixes, public vs. private assets, cache headers, and any Lambda or presigned URL flows. Note downstream consumers (mobile apps, third-party integrations) so you don't surprise them with URL changes. Decide what must stay public and what should become signed.

Step 2: Add UploadBird alongside S3

Introduce UploadBird as a second write target while leaving S3 untouched. In your upload handler, write to both for a short window. Use feature flags to control which URLs clients see. This ensures new uploads are already present in UploadBird before any cutover.

Step 3: Backfill existing objects safely

Copy historical objects in batches. Use checksums (ETag or MD5/SHA) to verify integrity. Preserve metadata like content type and cache control. Parallelize by prefix to respect rate limits and keep queues healthy. Log successes and retries so you have a clean report at the end.

Step 4: Gradual cutover

Start serving UploadBird URLs to a small cohort (internal users or a percentage of traffic). Watch error rates, latency, and cache hit ratio. Once stable, ramp the flag to 100%. Keep dual writes for a brief stabilization period, then turn off S3 writes.

Step 5: Update delivery and access

Replace presigned S3 URLs with UploadBird signed URLs for private content. For public assets, use UploadBird's CDN URLs with immutable paths so you avoid CloudFront invalidations. Update any hard-coded domains in emails, mobile apps, and webhooks.

Step 6: Decommission and simplify

Once traffic is stable, stop dual writes, lock the old buckets, and archive or delete them per your retention policy. Remove IAM roles, bucket policies, and CORS configs that are no longer needed. Update runbooks and on-call docs to point to UploadBird's status and audit logs.

What you gain

• No more presigned URL code paths—auth stays on your server, uploads stream to ours.
• Built-in malware/NSFW scanning and type/size enforcement without custom Lambdas.
• Smart CDN delivery with image/video optimization and signed URLs.
• Simpler bills: predictable tiers and transparent overages instead of egress roulette.

Migrations are scary when they're big-bang. Make it incremental, observable, and reversible, and you can leave S3 behind without the anxiety—or the CORS errors.