Slice-by-Slice vs Big-Bang: Choosing Your Bubble Migration Strategy

There are basically two ways to migrate a Bubble app: slice-by-slice, where you move one piece of the app at a time while the rest keeps running on Bubble, or big-bang, where you build the new app in parallel and switch everything over on a single cutover day.

The two strategies have very different risk profiles, very different effects on your business while the migration is running, and very different costs. This article walks through the trade-offs so you can pick the right one for your situation.

The slice-by-slice strategy

The slice-by-slice strategy (sometimes called the "strangler fig" pattern after the Martin Fowler post that named it) works like this:

1. Identify a vertical slice of the app - one feature, end-to-end
2. Rebuild that slice in the new code stack
3. Cut that slice over: the new app serves the slice, Bubble stops handling it
4. Repeat for the next slice until Bubble has nothing left to do
5. Final cutover: redirect DNS, archive the Bubble app

A "slice" is sized so each one takes 1-2 weeks of work and a few days of parallel-running for validation. Smaller is better.

The big-bang strategy

The big-bang strategy:

1. Build the entire new app in parallel
2. Migrate all the data in one final import
3. Cutover happens on a single chosen day - DNS flips, Bubble goes read-only, the new app takes over

The new app is live in one moment. Users may notice (depending on UI changes) but the business continuity is "we had a maintenance window from 8pm Friday to 2am Saturday."

Why slice-by-slice almost always wins

We use slice-by-slice for the overwhelming majority of migrations. Five reasons.

1. Risk is distributed, not concentrated

In a big-bang migration, all the risk concentrates into one moment. If something goes wrong at cutover, everything is broken. Auth, payments, search, every feature - all at once.

In slice-by-slice, the risk distributes across N small moments. If something goes wrong when the payments slice cuts over, only payments are affected. The rest of the app keeps running on Bubble while you fix it.

This isn't an edge case. Every migration has at least one cutover surprise. The question is whether you've spread that surprise across 10 small moments or compressed it into one large one.

2. Business continuity is preserved

During a slice-by-slice migration, your team is still shipping features. The slices that haven't been migrated yet are still on Bubble, where they're still editable.

During a big-bang migration, feature work largely stops for 4-6 months. Your team can't ship on Bubble (those changes won't make it into the new app) and can't ship on the new app (it's not yet live). Months of business momentum disappear into the gap.

For most companies, that's the difference between a successful migration and one that gets cancelled mid-project because the board lost patience.

3. Validation happens incrementally

In slice-by-slice, every slice has a real production audience right after it cuts over. Bugs surface within hours; you fix them while the team is still on that slice.

In big-bang, bugs surface for every feature simultaneously on the same day. The triage queue becomes unmanageable. Some bugs hide behind others. The team is burnt out by week three of post-cutover stabilisation.

4. The team learns the codebase progressively

Your engineering team learns the new stack by working on slice after slice. By cutover-of-the-whole-app time, the team has been writing TypeScript with the new patterns for months. They own it.

In big-bang, the team learns it all at once and is then expected to operate it from day one. Bugs at cutover get fixed by people who've never seen the production version of the code before.

5. The business can change its mind

Slice-by-slice means you can stop at any point. You've shipped some of the app on the new stack. If the business decides the migration isn't the right move anymore (priorities changed, runway shrunk, new product direction), you stop. What you've built is production-ready code you own.

In big-bang, stopping mid-project means you've spent months and have nothing live to show for it. The pressure to ship the big-bang on schedule creates worse decisions.

When big-bang IS right

There are three cases where big-bang beats slice-by-slice.

Case 1: very small apps

If the entire app is 5 Data Types, 20 workflows, and 3 pages, the overhead of running two systems in parallel exceeds the risk reduction. Rebuild it in 4-6 weeks and cut over. Big-bang is fine.

The threshold is roughly: if the whole rebuild would take less than 8 weeks, slice-by-slice's overhead isn't worth it.

Case 2: fundamental architecture changes

If you're not just moving to code - you're also fundamentally changing the data model in a way where slices can't run in parallel - big-bang might be unavoidable. For example: if you're moving from a single-tenant model to a multi-tenant model, you can't have half the app on each.

This is rare. Most architecture changes can be staged so slices still work.

Case 3: regulatory or contractual hard cutover

Sometimes a contract or regulator requires a clean cutover at a specific date. The new app has to handle 100% of traffic from a particular moment, with no parallel running. Big-bang is the only option, even though the risk concentration is worse.

We've seen this most often with healthcare and financial-services apps where the operating licence applies to specific stack components.

The hybrid that often works

There's a third option that doesn't get talked about often: slice-by-slice for most of the app, plus a big-bang cutover for one or two foundational pieces.

The pieces that usually fall into the big-bang bucket:

• Auth. Hard to have half users on Bubble auth and half on the new auth.
• The core entity model (the one or two Data Types every other feature references).
• The payment system, if it's deeply integrated everywhere.

These get migrated first, in a single concentrated cutover, before the slice-by-slice work on everything else starts. The "big-bang" piece is small enough that it's manageable, but it unblocks the slices that depend on it.

Almost all the migrations we run are actually this hybrid.

What this means for your timeline

Slice-by-slice migrations for a typical mid-stage Bubble app take 8-16 weeks of focused work, end to end. Big-bang migrations of the same app take 8-12 weeks (slightly less, because there's no parallel-running overhead) but with much higher risk.

If we quote a 12-week migration, most of those 12 weeks are spent on the slice phase. Discovery is 1-2 weeks, architecture is 2-3 weeks, foundation is 1 week, slice migration is 6-10 weeks, data migration is 1-2 weeks, cutover and partnership is 1 week + ongoing.

What to do next

If you want to figure out which strategy fits your specific app, book a 30-minute discovery call. We'll talk through your team's situation, your runway, and your risk appetite.

The migration playbook PDF walks through how we run the slice-by-slice approach in detail.

Read next: Bubble to Next.js migration guide and How to audit your Bubble app before migration.