# Core

Core is a set of systems (frontend, backend etc.) that Kibana and its plugins are built on top of.

## Integration with the "legacy" Kibana

Most of the existing core functionality is still spread over "legacy" Kibana and it will take some time to upgrade it.
Kibana is started using existing "legacy" CLI that bootstraps `core` which in turn creates the "legacy" Kibana server.
At the moment `core` manages HTTP connections, handles TLS configuration and base path proxy. All requests to Kibana server
will hit HTTP server exposed by the `core` first and it will decide whether request can be solely handled by the new
platform or request should be proxied to the "legacy" Kibana. This setup allows `core` to gradually introduce any "pre-route"
processing logic, expose new routes or replace old ones handled by the "legacy" Kibana currently.

Once config has been loaded and some of its parts were validated by the `core` it's passed to the "legacy" Kibana where
it will be additionally validated so that we can make config validation stricter with the new config validation system.
Even though the new validation system provided by the `core` is also based on Joi internally it is complemented with custom
rules tailored to our needs (e.g. `byteSize`, `duration` etc.). That means that config values that were previously accepted
by the "legacy" Kibana may be rejected by the `core` now.

Even though `core` has its own logging system it doesn't output log records directly (e.g. to file or terminal), but instead
forward them to the "legacy" Kibana so that they look the same as the rest of the log records throughout Kibana.