Updating sites to a new version from the engine

Question

CMS

How to make the mechanism for updating the engine correctly, given that any files and database structure can change on the site.
For example, there is an engine and 3 sites built on it.
On one site they found a bug, fixed it in the engine.
How then to transfer automatically to other sites, taking into account the fact that there could be edits in the files on the sites.

Answer 1

diff and patch. not?

Answer 2

From my bike experience.
Create an FTP account where updated files are stored by version numbers, example 35004
the folder contains
upd_conf.txt - a list of updated files, example 2. config_update.txt - a list of changes to make to the site config. in this case, the new release number The site itself has its own config, where the release number is registered. Write a php update check function that takes a version from its release, goes to ftp with updates, if there is a folder, then reads the list of changed files and loads them for itself. Updates the release number in the local config. If the site has personal improvements, then create a list of files prohibited for updates in the local config.
[files/onlineprice]
files = "index.php;price.exe"
[site/admpanel/catalog]
files = "adm_catalogID.php;tree.php"
[upload]
version="35004";