Can we run our old personalization and Croct in parallel while we cut over?
we cannot big-bang this. Our old Contentful personalization setup drives a lot of pages and I am not flipping all of them in one deploy with no way back.
What I want is slot by slot: put Croct on a few slots first, leave the rest serving the old way, and expand once each batch is proven. Is that a supported way to migrate, or does Croct expect to own all the slots at once? Rollback story matters to me here.
2 answers
Slot by slot is fine, it is actually the default way in. Adoption is gradual and there is no migration required: you wire a single slot, ship it, and expand from there. Croct does not need to own every slot to work.
The reason it is low risk is the fallback. Any slot Croct is not yet serving keeps rendering your existing Contentful content as the default, so the slots you have not touched behave exactly as they do today. Rollback for a migrated slot is just pointing it back at the Contentful entry. More on that split in keeping your content and moving only the experimentation layer.
We did precisely this. Ran Croct on a handful of slots for a few weeks while the rest of the site stayed on the old setup, watched them, then expanded once we trusted the numbers. No forced flip, no big deploy. Since Croct works alongside the existing stack rather than replacing the CMS, the two coexisting was never a problem.
Small bonus: the cut-over slots resolve server-side, so there is no flash of default content on them while the rest of the page still comes from the old path.
That is the reassurance I needed, thanks. Starting with three low-traffic slots and expanding from there.