What is Azure Service Bus? Understanding Azure’s Cloud Messaging System

on Microsoft, Microsoft Azure, Tutorials • April 8th, 2022 • Write for Hevo

Azure Service Bus- Featured Image

The internet has become the lifeline of connected people, technologies, applications, devices, and data across the globe. We now have a large number of distributed applications that can reach anywhere and use any amount of data to improve business efficiency, productivity, and, ultimately, customer satisfaction.

But setting up seamless communication between these applications has always been a challenge. Sometimes, APIs do the job, but in our 24×7 business service, how do you ensure asynchronous communication? What if your message sender and receiver aren’t available at the same time? Azure Service Bus is designed to overcome these kinds of challenges.

Microsoft Azure Service Bus is a highly-scalable and reliable Enterprise Messaging Service that connects many kinds of software, including cloud applications, on-premises applications, and Azure’s own services. Azure Service Bus can be used by local apps running behind a firewall, cloud applications, and client applications of any sort. In this guide, we’ll share all that is required to know about Service Bus, including its basics, features, users, integration, and pricing. 

Table of Contents

What Is Azure Service Bus?

Azure Service Bus Logo: Azure Service Bus
Image Source: Microsoft Azure

Microsoft Azure Service Bus is a Cloud-based Messaging as a Service (MaaS) Platform. It is a high-performance, real-time, and fault-tolerant service that transfers messages between your applications and databases securely. 

Microsoft Azure Service Bus can connect to any application, service, or a device running in the cloud and can establish communication with other applications, services, or receivers seamlessly. Blazoned with features like Advanced Messaging Queuing Protocol (AMQP), First-In, First-Out (FIFO) Messaging, Asynchronous Communication, and Publish/Subscribe capabilities, Azure Service Bus can reliably transmit instructions to all your applications to achieve your goals of application.

Key Benefits of Using Azure Service Bus

  • Reliable Cloud Messaging Service: Service Bus delivers a reliable, high-performance messaging system between applications and services even when they are offline. Using Azure Service Bus, you don’t have to weigh the burdens of  Server Management and Licensing. Since Azure Service Bus runs on the cloud, you can build, run, and manage messages between your applications with a single Microsoft-managed Global Cloud Site.
  • Multi-tenet Cloud Service: Microsoft Azure Service Bus is a Multi-tenet Messaging Service, which means that the service can be shared and used by multiple users. Each user can create a Namespace(s) and define communication mechanisms within that Namespace.
  • Scalability with Asynchronous Communication: Azure Service Messaging Bus provides Asynchronous Communication patterns to help you scale your business applications more reliably and securely, as well as make them run more smoothly under variable loads.
  • Complex Messaging Workflows Made Easy: Azure Service Bus makes complicated messaging workflows simple by constructing message topologies with complex routing. You may use this Azure Function Service Bus to send messages to numerous subscribers and spread them out to downstream systems at scale.

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Azure Service Bus Concepts

Before moving on, there are a few concepts that will be useful to understand.

  • Message: A message, that gets sent across applications, is a container that contains metadata and data. This data can be any type of information in formats like JSON, XML, Apache Avro, and Plain Text. 
  • Decoupling: Azure Service Bus Messaging Service decouples applications to improve reliability and scalability in communication between applications and services. This means that the sender and receiver don’t have to be online or readily available at the same time. Service Bus will store messages in the Queue, durably, until the receiver becomes available.
  • Load Balancing: Load balancing allows multiple users to read from a queue at the same time. It also enables senders and receivers to send and receive messages at different rates.
  • Transactions: Transactions allow users to perform multiple operations. For example, using Transactions, a user can obtain a message from a Queue, and post the results of processing to a set of a different query(s).

Azure Service Bus contains three messaging entities that form the core of its messaging capabilities. These three messaging entities are Queues, Topics, and Relays.

Queues

Queues allow one-directional communication. Each queue acts as an intermediary (also called a broker) that stores sent messages until the receiving application is available to receive and process them.

Queues: Azure Service Bus
Image Source: Microsoft Docs

Queues order incoming messages and label them with timestamps. Each incoming message is stored in triple-redundant storage and gets spread across availability zones if the Namespace is zone-enabled.

Topics

Topics provide one-directional communication using subscriptions. Like a Queue, an Azure Function Service Bus Topic acts as a broker, but it allows each subscription to see only messages that match specific criteria. Topics are useful in Publish/Subscribe Messaging Systems.

Topics: Azure Service Bus
Image Source: Microsoft Docs

Optionally, you can also define rules for a subscription. A subscription rule applies filters to define conditions for copying the message into the subscription. Using them, you can also define optional actions to modify your message metadata.

Relays

Relays provide bidirectional communication. Unlike queues and topics, a relay doesn’t store in-flight messages—it’s not a broker. Instead, it just passes them on to the destination application. All communication through Azure Function Service Bus Relays happens using Windows Communication Foundation (WCF). 

Relays: Azure Service Bus
Image Source: DotNetTricks

Namespaces

A Namespace is a scoping container for all messaging components – Queues, Topics, and Relays. It is essential and one of the initial stages to use Azure Service Messaging Services. Namespaces often serve as application containers, and multiple Queues and Topics can reside within a single Namespace.

Azure Service Bus Architecture

With the basics of Queues, Topics, Subscription, and Relays in place, let’s now move on to understanding the Azure Service Bus architecture.

The first step of communication starts with Publisher Apps; ones that create messages or information to be transmitted and received by receivers. As is shown in the figure, our first level of the hierarchy contains Web Applications that send messages to Queues. Queues store incoming messages until the receiving application is available to receive and process them. 

A message can also be sent through Azure Function Service Bus Topics. Topics can send out incoming messages to multiple, independent receivers using subscriptions. This mode of communication is displayed in the image from the sender Web Application 2. As mentioned earlier, users can define subscription rules to customize the message retrieval process based on desired parameters.

Our third communication flow in the image is using Relays. Relays have the ability to connect applications irrespective of their deployment environment. To establish the connection through Relays, each application creates an outbound TCP connection to Azure Service Bus. Unlike Queues and Topics, Relays don’t store messages. 

Azure Service Bus Architecture: Azure Service Bus
Image Source: DotNetTricks 

In order to use Azure Service Messaging Services, a user must first build a Namespace (container for messaging components) under their Azure subscription. A single Namespace can contain several components (Queues, Topics, and Relays). You can find more information about Namespace here – Namespaces.

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Advanced Features

Beyond the basic features, there are some more advanced features that Azure Service Bus offers to its users. There are as follows:

Message Sessions

Azure Service Bus enables combined and ordered handling of unbounded sequences of related messages. In simpler words, using Message Sessions, Azure Service Bus can organize large streams of messages into related messages and group messages from a specific client. Message Sessions can be used in First-In, First-Out (FIFO) patterns or  Request-Response patterns.

Auto-Forwarding

Auto Forwarding lets you reroute messages from the first Queue or Subscription to a second Queue or Topic that is part of the same Namespace. This helps in decoupling message senders from receivers and also aids in scaling individual Topics.

Dead-Lettering

The Dead Lettering Queue (DLQ) keeps track of messages that can’t be delivered to the receiver or ones that can’t be processed. You can inspect these messages from the DLQ and decide whether or not to remove them.

Scheduled Delivery

You can schedule messages for delayed processing in Queue or Topic using Scheduled Delivery. 

Filtering and Actions

Subscription rules define filters for copying the message into the subscription. Using them, you can define optional actions to modify your message metadata. You can also define which messages your subscribers want to receive from a Topic.

Duplicate Detection

Azure Service Bus can resend your message from the Queue or Topic to your receiver in case there’s any confusion. The Duplicate Detection feature then gets triggered and resends the message, discarding any previous messages or existing duplicates.

Auto-Delete On Idle

Microsoft Azure Service Bus automatically deletes your queue after a specified time interval called idle time interval. You can custom set your idle time interval, and the minimum duration is 5 minutes.

Shared Access Signature (SAS)

You can provide secure, delegated user access to your Azure resources via Shared Access Signature (SAS) control. With a SAS, you have fine control over how a client may access your data.

In addition to Shared Access Signature (SAS), Azure Service Bus also provides Role-based Access Control and Managed Identities, which allow you to construct a secure identity that can access secured resources. Using Azure Role-based Access Control, you grant custom permissions to your users for accessing specific Azure resources that your application needs.

Geo-Disaster Recovery

Your Azure Service Bus configuration is protected by geo-disaster recovery features. Geo-disaster recovery employs transparent failure detection and failover techniques in the event of a catastrophe or failure, ensuring that the stated service levels are maintained without noticeable pauses.

Compliance and Protocol

Azure Service Bus gets data point to point using Advanced Messaging Queuing Protocol (AMQP) 1.0. AMQP is an Open Standard Application Layer Protocol (ISO/IEC) standard that provides message orientation, queuing, routing, reliability and security. Azure Service Bus through AMQP enables organizations to develop cross-platform, hybrid applications using a vendor-neutral and implementation-neutral, open standard protocol.

Microsoft Azure Service Bus is also fully compliant with the Java/Jakarta EE Java Message Service (JMS) 2.0 API. It also supports the Java Message Service (JMS) 1.1 subset. The Java Message Service (JMS) 2.0 API allows Java programs to produce, transmit, receive, and read messages from an Enterprise Messaging System.

Service Bus Uses

It goes without saying that with all the features, benefits, and architectural knowledge of Service Bus in place, you would want to know the use cases where you can utilize Azure Service Bus and streamline your communication process.

Presented here is a list of instances when you can use Service Bus to gain its rewards:

  • Create a Queue to receive messages and delay message processing using Scheduled Delivery.
  • Handle peak loads where there is a surge of messages.
  • Decouple apps so that their technologies and APIs can evolve as long as they agree on the same message format for communicating with one another.
  • Distribute a single message to a number of different apps using Topics and Relays.
  • Scale-out message processing while keeping the sequence of the messages intact.

Integration

Azure Service Messaging Bus is part of Microsoft’s Cloud Offering Suite, which leverages a big advantage of integration with Azure Services and other Microsoft Apps. Listed below are the services that you can integrate with Service Bus:

  • Event Grid
  • Logic Apps
  • Azure Functions
  • Power Platform
  • Dynamics 365
  • Azure Stream Analytics

Recommended

Service Bus Standard vs Premium Messaging Tiers

Service Bus offers two plans – Standard Messaging and Premium Messaging. The main differences between the two are summarized in the following table.

Service Bus StandardService Bus Premium
Variable throughputHigh throughput
Variable latencyPredictable performance
Pay as you go pricing (Variable)Fixed pricing
No support for ScalingAbility to scale workload up and down as per business need
Send messages up to 256 KB in sizeSend messages up to 100MB in size
Table Source: Microsoft Docs

Conclusion

Azure Service Bus serves as a backbone of reliable, high-performance, and secure communication between applications. Not only can Service Bus implement complex workflows, but also using integration with Azure SQL Database, Azure Storage, and Web Apps, Service Bus Messaging Service can establish smoother operation even under variable loads.

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Have any questions on Service Bus? Do let us know in the comment section below. Also, share any other Microsoft Azure topics you’d want to use to cover. We’d be happy to know your opinions.

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