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

Core Plugin API Documentation:

• Core Public API
• Core Server API
• Conventions for Plugins
• Testing Kibana Plugins
• Kibana Platform Plugin API

Internal Documentation:

• Saved Objects Migrations

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.

core has its own logging system and will output log records directly (e.g. to file or terminal) when configured. When no specific configuration is provided, logs are forwarded to the "legacy" Kibana so that they look the same as the rest of the log records throughout Kibana.