When running Keycloak in environments such as Kubernetes, OpenShift, or on-premise, you want to protect the internal URLs from exposure to the public facing internet. You want to use your public hostname. This guide describes how to configure Keycloak to use the right hostname for different scenarios.
As this section explains, Keycloak exposes three API endpoint categories: frontend, backend, and administrative. Each category uses a specific base URL.
Frontend endpoints are used to externally access Keycloak. When no hostname is set, the base URL used for the frontend is taken from the incoming request. This choice has some major disadvantages. For example, in a high availability scenario, you may have multiple Keycloak instances. The choice of URL should not depend on the instance where the request lands. The URL should be used for all instances, so they are seen as one system from the outside.
Backend endpoints are used for direct communication between Keycloak and applications. Examples of backend endpoints are the Token endpoint and the User info endpoint. Backend endpoints are also taking the base URL from the request by default. To override this behavior, set the `hostname-strict-backchannel` configuration option by entering the `kc.start` command in this format:
When all applications connected to Keycloak communicate through the public URL, set `hostname-strict-backchannel` to true. Otherwise, leave this parameter as false to allow internal applications to communicate with Keycloak through an internal URL.
When `hostname-admin` is configured, all links and static resources used to render the Admin Console are served from the value you enter for `<adminHostname>` instead of the value for `<hostname>`.
To reduce attack surface, the administration endpoints for Keycloak and the Admin Console should not be publicly accessible. Therefore, you can secure them by using a reverse proxy. For more information about which paths to expose using a reverse proxy, see the <@links.server id="proxy"/> Guide.
When running Keycloak behind a reverse proxy, you may expose Keycloak using a different context path such as `myproxy.url/mykeycloak`. To perform this action, you can override the hostname path to use the path defined in your reverse proxy:
You run Keycloak in development mode by using `start-dev`. In this mode, the hostname setting is optional. When it is omitted, the incoming request headers are used.
In this example of using a curl GET request, the result shows the current OpenID Discovery configuration. All base URLS are taken from the incoming request, so `http://localhost:8080` is used for all endpoints.
