What is Azure Service Bus?

Microsoft Azure Service Bus is a fully managed enterprise integration message broker. Service Bus is most commonly used to decouple applications and services from each other, and is a reliable and secure platform for asynchronous data and state transfer. Data is transferred between different applications and services using messages. A message is in binary format, which can contain JSON, XML, or just text.

Some common messaging scenarios are:

  • Messaging: transfer business data, such as sales or purchase orders, journals, or inventory movements.
  • Decouple applications: improve reliability and scalability of applications and services (client and service do not have to be online at the same time).
  • Topics and subscriptions: enable 1:n relationships between publishers and subscribers.
  • Message sessions: implement workflows that require message ordering or message deferral.

Namespaces

A namespace is a scoping container for all messaging components. Multiple queues and topics can reside within a single namespace, and namespaces often serve as application containers.

Queues

Messages are sent to and received from queues. Queues enable you to store messages until the receiving application is available to receive and process them.

Queue

Messages in queues are ordered and timestamped on arrival. Once accepted, the message is held safely in redundant storage. Messages are delivered in pull mode, which delivers messages on request.

Topics

You can also use topics to send and receive messages. While a queue is often used for point-to-point communication, topics are useful in publish/subscribe scenarios.

Topic

Topics can have multiple, independent subscriptions. A subscriber to a topic can receive a copy of each message sent to that topic. Subscriptions are named entities, which are durably created but can optionally expire or auto-delete.

In some scenarios, you may not want individual subscriptions to receive all messages sent to a topic. If so, you can use rules and filters to define conditions that trigger optional actions, filter specified messages, and set or modify message properties.

Advanced features

Service Bus also has advanced features that enable you to solve more complex messaging problems. The following sections describe these key features:

Message sessions

To realize a first-in, first-out (FIFO) guarantee in Service Bus, use sessions. Message sessions enable joint and ordered handling of unbounded sequences of related messages.

Auto-forwarding

The auto-forwarding feature enables you to chain a queue or subscription to another queue or topic that is part of the same namespace. When auto-forwarding is enabled, Service Bus automatically removes messages that are placed in the first queue or subscription (source) and puts them in the second queue or topic (destination).

Dead-lettering

Service Bus supports a dead-letter queue (DLQ) to hold messages that cannot be delivered to any receiver, or messages that cannot be processed. You can then remove messages from the DLQ and inspect them.

Scheduled delivery

You can submit messages to a queue or topic for delayed processing; for example, to schedule a job to become available for processing by a system at a certain time.

Message deferral

When a queue or subscription client receives a message that it is willing to process, but for which processing is not currently possible due to special circumstances within the application, the entity has the option to defer retrieval of the message to a later point. The message remains in the queue or subscription, but it is set aside.

Batching

Client-side batching enables a queue or topic client to delay sending a message for a certain period of time. If the client sends additional messages during this time period, it transmits the messages in a single batch.

Transactions

A transaction groups two or more operations together into an execution scope. Service Bus supports grouping operations against a single messaging entity (queue, topic, subscription) within the scope of a transaction.

Filtering and actions

Subscribers can define which messages they want to receive from a topic. These messages are specified in the form of one or more named subscription rules. For each matching rule condition, the subscription produces a copy of the message, which may be differently annotated for each matching rule.

Auto-delete on idle

Auto-delete on idle enables you to specify an idle interval after which the queue is automatically deleted. The minimum duration is 5 minutes.

Duplicate detection

If an error occurs that causes the client to have any doubt about the outcome of a send operation, duplicate detection takes the doubt out of these situations by enabling the sender to re-send the same message, and the queue or topic discards any duplicate copies.

SAS, RBAC, and Managed identities for Azure resources

Service Bus supports security protocols such as Shared Access Signatures (SAS), Role Based Access Control (RBAC) and Managed identities for Azure resources.

Geo-disaster recovery

When Azure regions or datacenters experience downtime, Geo-disaster recovery enables data processing to continue operating in a different region or datacenter.

Security

Service Bus supports standard AMQP 1.0 and HTTP/REST protocols.

Client libraries

Service Bus supports client libraries for .NET, Java, JMS.

Integration

Service Bus fully integrates with the following Azure services:

Next steps

To get started using Service Bus messaging, see the following articles: