A Failover backend defines failover behavior within a list of referenced
backends. Traffic is sent to the first backend in the list. If that backend
is offline or no connection can be established, ngrok attempts to connect to
the next backend in the list until one is successful.
A Weighted Backend balances traffic among the referenced backends. Traffic
is assigned proportionally to each based on its weight. The percentage of
traffic is calculated by dividing a backend’s weight by the sum of all
weights.