uiSettings should throw an error on unknown overrides

[TinaHeiligers]

Part of #48925

The uiSettings.overrides setting which (when stored in kibana.yml or passed as config args when starting Kibana) allows forcing some uiSettings to always have a specific value. This setting accepts a map of uiSetting keys to values that will always be used to override whatever is stored in the config saved object. In #59694 we enforced validation on write, thereby preventing invalid values from being read or written.

Kibana should protect against unknown settings that are added or overwritten using the uiSetting.overrides.<key> in kibana.yml.

Potential side effects

There's at least two cases where introducing an exception would be a problem:

• Any settings that have been removed from the codebase but are still present in the user's config
• Any settings that belong to a plugin that was enabled but is now disabled. We should handle this case carefully.

[elasticmachine]

Pinging @elastic/kibana-core (Team:Core)

[pgayvallet]

Any settings that have been removed from the codebase but are still present in the user's config

Any settings that belong to a plugin that was enabled but is now disabled. We should handle this case carefully.

Should we just output a warning, and ignore the unknown settings, instead of throwing an error then? It sounds safer.

[afharo]

I would expect a similar behaviour to any non-valid configuration keys. The current behaviour when adding a non-valid key is that Kibana throws an error and stops working. Shouldn't we do the same here?

[pgayvallet]

One could argue that uiSetting.overrides is the configuration key, and that it contains a single value, the map of overrides, so it would be acceptable to have a different behavior.

But honestly, I would be fine either way. My main concern about throwing is, as Tina said, the risk when settings got deleted and the overrides still present in the config file, OTOH that feature is not even documented, and having to remove the key after a version bump seems acceptable.

[TinaHeiligers]

With a fully managed offering, uiSettings overrides will no longer be a concern. As such, closing this issue as stale.