Modules
Modules are Odoo's unit of functionality. Antelao shows you what each database has installed, and lets you install, update, disable and uninstall them without opening Odoo's own interface.
Where to look
In the Web UI, Databases → a database → Modules. Each module has a detail page showing its version, state, and where it came from: Odoo's own addons, Enterprise addons, or one of the instance's Git repositories.
prod-1# odoocli instance database modules --instance acmeInstalling and updating
prod-1# odoocli instance modules install --instance acmeInstalling and updating are background jobs. They take an exclusive lock on the instance, so nothing else runs against it while Odoo's registry is being rebuilt.
Updating a Git-backed module fetches the repository, pins the retrieved commit, and rebuilds. See Git addons for why the commit rather than the branch is what gets recorded.
Disabling and uninstalling
In Odoo, disabling a module can remove data belonging to that module, exactly as uninstalling can, and re-enabling does not bring it back.
Take a backup of the database first. Not a backup of the instance later, and not "there is a nightly one": a backup of this database, before this change.
Antelao asks for explicit confirmation for both, and the confirmation is not a formality.
Database groups
Databases can be organised into groups, which is how a hosting company keeps one customer's databases together across instances. Groups are visible on Databases → Groups, and a group's detail page lists its databases and the modules across them.
The practical use is answering "which of my customers are on this module version" without walking every database by hand.