When building distributed applications, one of the most important design decisions is how services will communicate.
Azure Service Bus gives us two powerful messaging patterns: Queues and Topics. While they might seem similar at first, they serve very different purposes depending on the scenario.
In this article (Day 2 of the series), let’s break down the differences, real-world use cases, and .NET implementation for both.
🔹 Azure Service Bus Queue
A Queue is a point-to-point communication channel:
One sender → One receiver
Messages are stored until a receiver picks them up.
Processed in FIFO (First-In, First-Out) order.
👉 Use Queues when you want to ensure only one consumer processes a message.
✅ Real-world example:
An order processing system where each order should be handled by one service instance.
🔹 Azure Service Bus Topic & Subscriptions
A Topic is like a broadcast system.
One sender → Multiple receivers
A message is sent to the Topic, and multiple Subscriptions can receive it.
Each subscription can apply filters (only get the messages it cares about).
👉 Use Topics when you want multiple services to react to the same event.
✅ Real-world example:
A payment event:
Billing system → logs the payment.
Notification system → sends receipt email.
Analytics system → updates dashboards.
🔹 Code Example in .NET
🔹 Wrapping Up
Queue = One-to-one communication.
Topic = One-to-many communication.
Both are durable, scalable, and reliable messaging patterns in Azure Service Bus.
👉 The right choice depends on whether your message should go to one service or many services.
💬 Which messaging pattern have you used more in your projects — Queues or Topics?
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