Will the site or app go offline during the migration?

It should not. The old and new systems run in parallel and traffic moves across gradually, so users keep working while the migration happens.

Will we lose search rankings?

Not when the move is planned properly. Every URL gets a redirect, metadata and structured data are carried across, and the site is crawled before and after cutover to catch gaps.

How do you keep data consistent?

Replication or dual writes keep both systems in step while they are live, then row counts and checksums confirm nothing is missing before the old database is retired.

Can we keep shipping features during the migration?

Yes. Because the work moves module by module, your team can keep releasing on the parts that have not moved yet.

How long does a migration take?

It depends on size and how tangled the old code is. After a short audit you get a staged plan with a timeline per module, rather than one big launch date.