Mitigating Webhook Event Amplification in Multi-Tenant SaaS Integrations Using Delta-Validated Event Propagation

Multi-tenant Software-as-a-Service (SaaS) platforms rely on webhook change notifications from cloud APIs such as Microsoft Graph to synchronize calendar and resource-booking data in near-real time. Empirical analysis reveals a structural failure in this model, which we term webhook event amplification: a single state mutation triggers a burst of unordered notifications carrying no deduplication token. Controlled measurement shows the provider delivering approximately nine times the notifications the subscription model warrants, reaching a mean of 53 notifications per mutation in the most severe configuration. Left unmitigated, this exhausts downstream compute, degrades observability, and introduces race conditions that compromise transactional idempotency. Because the provider studied here offers no native suppression, deduplication, or ordering at the delivery layer, remediation must occur at the subscriber edge; delta queries provide an authoritative state-retrieval mechanism but are not described as an inline notification-deduplication path. This paper introduces the Distributed Notification Broker (DNB), which interposes a four-stage filtering pipeline between the webhook source and downstream consumers, combining tenant-isolated partition-keyed streaming, delta-validated event propagation, and business-contract change detection so that only verified, business-relevant changes propagate. Empirical evaluation over a 78-day observation period demonstrates an 88% reduction in downstream processing volume, a substantial reduction in concurrency-induced race conditions restoring system stability, an 89% reduction in volume-attributable infrastructure cost, and a 68% reduction in total infrastructure cost.