config.php should not need to be writable

Currently a few fields in config.php are expected to be writable:

• instanceid (during first install)
• maintenance (when doing upgrades/etc)
• version (when doing upgrades)

Of these fields, version and instanceid should be in the database. as they are strongly tied to the rest of the application state which is in the database.

setting maintenance in the database could make sense as well, if it is assumed that inaccessable db means maintenance => true

Either way the first two issues cause problems when trying to manage nextcloud in a modern cloud-native way (https://github.com/nextcloud/docker/issues/2044).

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Start with config.php and trace how instanceid, maintenance, and version are written during first installation and upgrades. Review the linked nextcloud/docker issue for the cloud-native deployment context. Done means these fields no longer require a writable config.php, while their database persistence and maintenance behavior are defined.