In general, there are two approaches to perform a failover: manual and automated.

Manual approach

In the manual approach, the operator selects the new leader node and instructs all the nodes accordingly. This is the safest approach, but it incurs significant downtime.

Automated approach

An alternative is an automated approach, where follower nodes detect that the leader node has crashed (e.g., via periodic heartbeats), and attempt to elect a new leader node. This is faster but is quite risky. This is because there are many different ways in which the nodes can get confused and arrive at an incorrect state.