DELIVERY WITHOUT DROPPED EVENTS.

A production-oriented last-mile delivery platform built as a modular monolith with five independently structured modules, communicating through RabbitMQ and gRPC with Transactional Outbox and Inbox reliability.

1. 01 / SECTION

   THE PROBLEM

   When asynchronous parts of a system communicate, failures can happen between changing application state and publishing the event that describes that change.

   A dropped event in last-mile logistics means a driver is never notified, a dispatch never happens, or a customer never receives a status update — while the database says everything is fine.

2. 02 / SECTION

   THE APPROACH

   Transactional Outbox and Inbox patterns keep state changes and message processing reliable while protecting consumers from duplicate message handling.

   Domain events are written inside the same transaction as the state change, then relayed to RabbitMQ through MassTransit. Consumers deduplicate with an inbox so repeated deliveries stay safe.

3. 03 / SECTION

   MODULE BOUNDARIES

   Five modules — Orders, Drivers, Dispatching, Tracking and Notifications — each own their data and expose explicit contracts instead of sharing internal state.

   Dispatching and Drivers communicate synchronously over gRPC with Protocol Buffers where an immediate answer is required; everything else flows asynchronously over the message bus.

4. 04 / SECTION

   OUTCOME

   The platform keeps order state and delivery events consistent across modules even when parts of the system fail or retry mid-flow.

   Boundaries stay understandable as the system grows, and each module can be reasoned about, tested and evolved independently.