When using microservices architecture, you’ll likely need to incorporate messaging services to enable decoupling of your services. Azure offers a few messaging services: Azure Event Grid, Azure Event Hubs, Azure Storage queues and Azure Service Bus. Each of these services is designed for specific scenarios, and understanding the differences between them will help you choose the right one for your application. In many cases, these services can be used together to complement each other.
Events vs. Messages
Before diving into the details of each messaging service, let’s clarify the distinction between events and messages. An event is a lightweight notification of a condition or a state change – something that has already happened. The publisher of the event has no expectation about how the event is handled, and the consumer decides what to do with the notification. Events can be discrete units or part of a series.
On the other hand, a message is raw data produced by a service to be consumed or stored elsewhere. The message contains the data that triggered the message pipeline, and there is a contract between the publisher and the consumer on how the message should be handled. In other words, a message is a request for action.
Now that we have a clear understanding of events and messages, let’s explore each Azure messaging service in more detail.
Azure Event Grid
Azure Event Grid is an eventing backplane that enables event-driven, reactive programming. It follows the publish-subscribe model, where publishers emit events without any expectations on how they are handled, and subscribers decide which events they want to handle. Event Grid is deeply integrated with Azure services and can also be added to your own applications.
One of the key benefits of Event Grid is its ability to simplify event consumption and reduce costs by eliminating the need for constant polling. It efficiently and reliably routes events from Azure and non-Azure resources to registered subscriber endpoints. Event Grid provides the necessary information to react to changes in services and applications, but it does not deliver the actual object that was updated.
Azure Event Grid supports both push and pull models. In the push model, Event Grid delivers (pushes) events to subscribers. With this model, you will need to ensure that your subscribers are able to handle all the messages pushed, otherwise you might need to implement way to handle the backpressure. In the pull model, subscribers pull events from Event Grid at their own pace.
Event Grid is a great choice when you want to react to discrete events that occur in Azure services or your own applications.
Azure Event Hubs
Azure Event Hubs is a big data streaming platform and event ingestion service. It is designed to handle high-throughput, real-time data streams from various sources. Event Hubs can receive and process millions of events per second, making it an ideal choice for scenarios that require capturing, retaining, and replaying telemetry and event stream data.
Event Hubs provides low-latency event ingestion and enables the capture of streaming data for further processing and analysis. It can be seamlessly integrated with various stream-processing infrastructures and analytics services. Whether you need real-time processing or repeated replay of stored raw data, Event Hubs offers a scalable solution.
Event Hubs is a great choice when you need to ingest and process high-volume event streams.
Azure Storage Queue
Azure Storage queue is a simple message queuing service that stores large numbers of messages that can be accessed from anywhere in the world via authenticated calls using HTTP or HTTPS. A queue message can be up to 64 KB in size, and a queue can contain millions of messages, up to the total capacity limit of a storage account.
Storage queues are very primitive and do not support any advanced features such as message ordering, duplicate detection, or dead-lettering. However, they are very cost-effective and can be used to decouple applications and services. Storage queues are a great choice when you need a simple, reliable, and inexpensive messaging solution.
Azure Service Bus
Azure Service Bus is a fully managed enterprise message broker that provides reliable message delivery with support for message queues as well as publish-subscribe topics. It is designed for enterprise applications that require features like transactions, message ordering, duplicate detection, and instantaneous consistency.
Azure Service Bus acts as a brokered messaging system, storing messages until the consuming party is ready to receive them. It is an ideal choice for scenarios that involve high-value messages that cannot be lost or duplicated. Azure Service Bus also facilitates secure communication across hybrid cloud solutions and enables the connection of on-premises systems to cloud solutions.
Service Bus is a great choice when you need a fully managed enterprise messaging service with advanced features.
Choosing the Right Messaging Service
- Azure Event Grid: Event Grid is best suited for reactive programming scenarios that involve event distribution, allowing you to react to status changes in your services or applications. It is particularly useful for serverless solutions that require scalability and cost efficiency.
- Azure Event Hubs: Event Hubs is designed for big data streaming scenarios, where high-throughput, real-time data ingestion is required. It is an excellent choice for capturing and processing telemetry and event stream data from multiple sources.
- Azure Storage queue: Storage queues are a simple, reliable, and cost-effective messaging solution. They are a great choice for decoupling applications and services, and they can be used to implement asynchronous processing or reliable communication between components.
- Azure Service Bus:Service Bus is the go-to messaging service for enterprise applications that require reliable message delivery, support for transactions, ordering, and advanced messaging features. It provides the necessary infrastructure for seamless communication between cloud and on-premises systems.
While each messaging service has its specific use cases, it’s important to note that they can also be used together to fulfill distinct roles or form an event and data pipeline.
In this post, I introduced some of the messaging services available in Azure and discussed their key features and use cases. I hope this post helps you choose the right messaging service for your application. In the next series of posts, I will show how to use each of these messaging services in .NET. If you have any questions or comments, please leave them in the comments section below. Thanks for reading!