Event-driven service communication

Services called each other synchronously over HTTP. A slow or unavailable downstream service would block callers and cascade into user-facing failures, and the tight coupling made each service hard to change in isolation.

• Introduced MassTransit with RabbitMQ as the messaging backbone for cross-service communication.
• Moved suitable workflows to publish/subscribe events and consumers instead of blocking request/response.
• Added background consumers for integration work so third-party calls happen off the request path.
• Configured retry and fault handling so transient downstream failures recover instead of surfacing to users.

• Services are decoupled: one being slow or down no longer blocks the others.
• Integration and long-running work moved off the request path, improving perceived responsiveness.