You can find the configuration for doing that in the [[database]]({{<relref"../administration/configuration.md#database">}}) section in the Grafana config.
Grafana will now persist all long term data in the database. How to configure the database for high availability is out of scope for this guide. We recommend finding an expert on for the database you're using.
Currently alerting supports a limited form of high availability. [Alert notifications]({{< relref "../alerting/notifications.md" >}}) are deduplicated when running multiple servers. This means all alerts are executed on every server but alert notifications are only sent once per alert. Grafana does not support load distribution between servers.
Grafana uses auth token strategy with database by default. This means that a load balancer can send a user to any Grafana server without having to log in on each server.