Event Message

Introduction

Event-type messages intend to notify about an event that happened in the sender’s system like ORDER_CREATED.

The body contains all the required details about the event.
The document can be the detail.
unlike with identifier type events, it requires no extra API calls. which reduces the receiver’s dependency on the sender.
Useful When: the sender does not store events in the database.
Drawback: data loss if the service dies before publishing the event.

The body only contains the ID.
Id can reference the event log or entity in the sender system.
After receiving the event, the receiver makes an API (RPC) call to the sender to get details.
Useful When:
- The receiver is only interested in the last state of the data.
- or the sender stores all the event logs in the database. (state change).
Drawback:
- Requires an extra API call from the receiver service.
- Increases the receiver service dependency on the sender service.
- What If data gets changed before the receiver reads it? Example: In a credit card system receiver gives rewards when the available balance reaches a certain threshold.