Quorum

1. The Incident

The previous two lessons coordinated different services performing different work. This lesson and the next address replicas that store the same data and must determine its current value.

The store's cart no longer satisfies the primary-replica design because of failover. Failover promotes a replica after the primary stops. Cart promotion takes about 30 seconds, during which no customer can add any item.

Many datasets can tolerate a 30-second write pause, but carts directly affect revenue