Loyalty glossary · 8. Technology and architecture (25)
Event Driven Architecture
Event driven architecture is a design pattern where loyalty system components communicate by emitting and reacting to discrete business events, such as a point accrual or a tier change, rather than by direct calls that wait for a response. This decouples the systems that cause changes from those that enforce rules.
Event driven architecture is the only practical way to build a loyalty programme that survives peak earn seasons. Point balances are write heavy, not read heavy. A synchronous call that updates a balance and then waits for a response will collapse under a Black Friday flight booking wave, because every accrual becomes a queue of waiting threads. The loyalty operators that avoid outages are the ones that treat each accrual as an event, not as a database row.
Two events matter most in a loyalty programme. The accrual event records points earned, partner, and time. The activity-based-qualification event records a behaviour that might move a member toward a tier, such as a stay or a flight segment. These events must not share a synchronous transaction. A qualification check that queries the accrual ledger directly will block the accrual stream during peak hours, and the programme will lose data before it loses members.
Work the arithmetic, because architecture decisions live or die on numbers. Consider a programme that records 2 million stays per year. Each stay earns an average of 750 points, so the accrual stream carries 1.5 billion points per year. A 0.5 percent event loss rate drops 7.5 million points annually, and the actuarial model then understates the liability by the same amount. Move to a 0.1 percent loss rate and the error falls to 1.5 million points.
Event driven architecture pays off in replay. An event log is the system of record, so a new accrual rule or a retroactive tier change is applied by replaying the past, not by patching the present. The alternative, a synchronous ledger of current balances only, cannot answer why a member reached a tier, and that is why activity-based-qualification programmes fail audit.
Most loyalty platforms claim to be event driven but are not. They publish events as side effects after a central service has already mutated the balances. If the event bus fails, the balances still change, so the events are not the truth. The test is simple: delete the event and see whether the balance changes. In a real event driven architecture, deleting the event erases the world. In the fake version, deleting the event only erases the history.