How to Migrate AWS S3 Buckets Without Downtime or Broken CloudFront URLs

Most teams can move data across AWS. But when your S3 buckets are serving production traffic through CloudFront, the stakes are much higher. Breaking asset paths or introducing lag isn't an option.

When one of our clients needed to migrate millions of static web assets across AWS accounts, we delivered a complete, infrastructure-as-code migration — with no downtime, no broken links, and no support tickets after launch.

Here’s how we pulled it off.

A Migration Without Room for Error

The goal was simple on paper: move large-scale S3 storage from a set of legacy AWS accounts to a new, consolidated organization. But the requirements made it complex.

Everything had to continue working mid-flight. Object keys couldn’t change. CloudFront behaviors had to remain identical. Even advanced routing, headers, and cache policies needed to match — all while users continued to load assets in real time.

This wasn’t just a data transfer. It was a systems-level handoff.

Designing for Safety and Scale

We approached this like a product launch, not a one-off script.

Instead of manual steps, we defined every part of the migration in Terraform — including S3 buckets, IAM roles, CloudFront configurations, and replication settings. Our Jenkins pipelines handled automation from replication to validation. Python scripts compared object parity and scanned logs via Athena to confirm there were no blind spots.

Everything ran behind the scenes while production traffic stayed routed through the original setup.

Building the Blue-Green Architecture

To prevent disruption, we deployed a blue-green architecture. The new S3 environment and CloudFront origins were spun up in parallel. We used live access logs and preview headers to test responses without routing live traffic. Only once every behavior matched — including cache headers, origin paths, and response times — did we flip DNS to point to the new environment.

Rollback was always an option, but we never had to use it.

How We Knew It Worked

No migration is safe without deep validation. We combined CloudFront log scanning, S3 object comparison, and direct file access testing to ensure everything was consistent. Even metadata and edge-case content like redirects and versioned objects were verified against the original setup.

The result? Not a single broken path, asset error, or user disruption.

Outcomes That Stick

After launch, performance stayed consistent. CloudFront hit rates remained high. And the infrastructure became fully manageable through code — no more guesswork, no more legacy risk.

The team can now evolve their asset pipeline with full confidence, backed by observability and version control.

What This Means for Enterprise Teams

S3 migrations at scale require more than file movement. They demand orchestration, rollback plans, and a full understanding of how storage, caching, and DNS interact.

We’ve seen firsthand how a thoughtful, code-first approach makes these migrations not only possible but safe — even with millions of files and multiple environments in play.

If your current setup is holding back performance, flexibility, or security — you don’t have to rip and replace overnight. You just need a strategy built on clarity and control.

Want to modernize without the risk?

Let’s talk through your storage and delivery pipeline. We’ll help you plan for zero surprises.