Contao 5 Zero-Downtime Migration: Official Upgrade Bundle vs Custom Scripts

Goal

Migrate a small Contao 5 application to a newer minor release without user-facing downtime.

Constraint

Contao 5 offers maintenance mode through the install tool, but enabling it locks the site and can be perceived as downtime. Blue-green requires two identical environments; rolling update keeps old and new code together and risks schema or cache mismatches during transition.

Uncertainty

The official Contao upgrade bundle handles schema changes automatically, but it may tie the app to a specific core version and reduce flexibility for a small app. Custom scripts preserve control yet require manual schema updates and cache clearing.

This behavior needs confirmation against current Contao documentation before production planning.

Can the official Contao upgrade bundle apply schema changes on Contao 5 without activating maintenance mode?

For a single-server deployment, is a custom migration script preferable to maintaining a parallel blue-green environment?

What cache-clearing behavior is expected when old and new Contao versions share the same database during transition?