Configuration is in toml format and is read from config/settings.conf or as specified with -config <file>. You may also use container secrets for the configuration, deployed as settings. Additionally you can pass overrides to most settings using env variables.
By default the site service has the configuration for the whole system and other services fetch its configuration over the backend message bus. For that they need to know the BACKEND_URL when starting up.
Configuration settings are validated, any invalid keys are refused and reported.