What actually moves and how we cut over
Inventory the old environment
A CodeIgniter application is more than its repository. Before touching anything we record the PHP release and extensions, the web server rewrite rules, cron jobs, outgoing mail configuration, file permissions on logs and cache folders, and any absolute paths or IP addresses written into config files. On CodeIgniter 3 that means reading config.php, database.php and any environment subfolders. On CodeIgniter 4 it means the .env file and the writable directory. Surprises found here are cheap. The same surprises found on cutover night are not.
Data, files and sessions
Databases are moved with a full dump for rehearsal and a final sync at cutover. We check character sets and collations before import, because a mismatch corrupts accented names and currency symbols in ways nobody notices for days. After each load we compare row counts and checksums per table. Uploaded files are copied in advance and topped up at the end. If they are going to object storage, the code that builds file URLs is changed in one place and old paths are redirected. Sessions stored as files on the old server will not exist on the new one, so we either move session storage to the database beforehand or accept a single re-login and warn users.
When the destination is Laravel
Leaving CodeIgniter is justified when the product needs things Laravel provides as standard: queues, a scheduler, events, broad package support and a large hiring pool. It is not justified by fashion. We almost never recommend a big-bang rewrite. The safer route is to stand Laravel up beside the existing application, point it at the same database, share login state between the two, and move one section at a time behind the same domain. Eloquent models are mapped onto the existing tables first, and schema cleanup comes later, once the old code no longer reads them. Our Laravel migration page describes that side in more detail.
Cutover is a script
The switch itself follows a written runbook that has already been executed at least once on staging. DNS time-to-live is lowered days ahead. At the agreed hour the old site goes into maintenance mode, the final database and file sync runs, checks pass, and traffic moves. The old server stays intact and reachable for an agreed period. If a serious problem appears, the runbook includes the steps to point traffic back.
After the move
For the first days we watch error logs, slow queries, mail delivery and cron output closely. Old hosting is cancelled only after you confirm that month-end or another full business cycle has run cleanly. If the migration also exposed deeper code problems, legacy PHP modernization is the next conversation.