Understanding When to Use Azure Service Bus Queues or Topics
If you’re finding it challenging to decide when to use Azure Service Bus Queues or Topics, this blog is for you!
In our previous blog, we explored Azure Service Bus Queues, Topics, and Subscriptions. To recap, Azure Service Bus is a fully managed messaging service provided by Microsoft Azure. It helps decouple and scale applications by allowing different components to communicate with each other through messages.
In this blog, we will delve deeper into Azure Service Bus Queues vs. Topics, examining their differences, use cases, and how to choose between them based on your application needs. By understanding these core concepts, we’ll be better equipped to design scalable and efficient messaging solutions using Azure Service Bus.
Azure Service Bus Queues vs. Topics
Service Bus Queues
Queues work on a First In, First Out (FIFO) basis. This means that clients that receive messages from the queue and then process that message in the order in which they were added to the queue, and they will be the only consumer that processes this message. The queue will store this message until our client is able to process them. To process the message, the client will pull the message off the queue.
Purpose: Queues are designed for point-to-point communication. They are ideal when a single consumer needs to process messages from a single sender.
Message Handling: Messages are stored in a queue and processed by a single consumer in a first-in, first-out (FIFO) manner.
Use Case: Best suited for scenarios where a specific task needs to be handled one at a time. For example, in an order processing system where each order needs to be managed sequentially.
Fig – Message Queue with Messages
One of the benefits of using queues is that producers and consumers do not need to exchange messages simultaneously. Messages are stored in the queue and are processed only when the consumer retrieves them. This setup enables producers to continue sending messages to the queue independently. Consequently, components within our architecture can be decoupled, as producers and consumers are not required to synchronize their actions. If there is a high volume of messages entering the queue, we can scale up the consumers without needing to scale the producers.
Service Bus Topics
Topics are different to Queues since instead of working with a single consumer, we can have multiple subscribers to our topic, who will receive their own copy of the message from the topic. This works in a pub/sub pattern, where we will have messages being published to the topic and have multiple clients subscribe to that topic.
Purpose: Topics are designed for publish-subscribe communication. They allow messages to be sent to a topic and processed by multiple consumers.
Message Handling: Messages sent to a topic are delivered to multiple subscriptions. Each subscription can have its own filter and process messages independently.
Use Case: Ideal for broadcasting messages to multiple systems. For instance, a CRM system might need to notify various departments (e.g., sales, marketing) about a new customer record.
Fig – Topic with three Subscription with Messages
In Topics, our consumers don’t directly consume the message from our Topic. Instead, we create subscriptions that subscribe to the topic and our consumers receive a copy of a message from the topic. In Azure Service Bus, we can define filters on these subscriptions that determine conditions for messages to be published to a subscription and actions that modifies the message metadata.
Conclusion
In this post, we discussed the differences between Queues and Topics in Azure Service Bus. To summarize, Azure Service Bus Queues are ideal for point-to-point communication in which messages must be handled sequentially by a single consumer. Topics, on the other hand, are suitable for scenarios that need publish-subscribe patterns, as they enable several consumers to process the same message independently. Choosing the proper solution is determined by your application’s, individual requirements, ensuring that your message system is both scalable and efficient. If your system requires sequential processing and single customers, queues are the best option. However, if your system wants to broadcast messages to several users, Topics will give the necessary flexibility and scalability.
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