Callback Event

Overview

Meaning and scope

Callback Event is the structured event message delivered through a callback when a monitored operation changes state or reaches a defined condition. It is used to communicate the event type and relevant data to the receiving application. It differs from the callback transport, which is the delivery mechanism rather than the business event itself.

Mechanism and operation

The sender assigns an event identifier and type, includes object and status data with timestamps and version, and delivers it to the configured target. A receiver should treat transport acknowledgement and successful downstream processing as separate states for Callback Event. Important failure modes include ambiguous event names, mutable payloads, missing sequence context, duplicate delivery, and schema changes. Operational evidence should include event ID, type, object ID, previous and new state, created time, schema version, and delivery attempts. Callback Event should be documented alongside Callback, Callback Response, and Callback Verification.

Practical payment example

A checkout webhook carries a paid status transition and event identifier; the merchant verifies and deduplicates it before fulfillment.

Operational checks

Business actions triggered by Callback Event should be idempotent and should verify the current object state before fulfillment or accounting updates. Monitoring for Callback Event should track delivery age, signature failures, duplicate rate, retry exhaustion, and unresolved business events. Replay of Callback Event should preserve original identifiers and timestamps so historical processing cannot masquerade as a new event.

Distinctions and limits

Common risks include ambiguous event names and mutable payloads. A Callback Event handler should acknowledge only after durable receipt when the provider’s retry contract depends on the response.

Related reading

Related definitions: Callback, Callback Response.