Azure Service Bus

 1. Overview

• Message broker
• Can decouple applications and services
• Some common scenarios:
• Messaging: Transfer business data
• Decouple application: client and server don’t have to be online at the same time.
• Topic and subscriptions: enable  1:n relationships between publisher and subscriber.
• Message session: implement workflows that require message ordering or message deferral.

2. Queue

• FIFO
• Use case: point to point communication

3. Topic

• Topic and subscription: subscription as a virtual queue of a topic. Each subscription receive a copy message

4. Receive Mode

• Default is PeekLock mode
• Receive mode: ReceiveAndDelete  and PeekLock
• ReceiveAndDelete:
• Service bus mark message as being consumed
• The application can tolerate not processing a message if a failure occurs  
• PeekLock
• two-stage
• it possible for the application cannot tolerate missing messages.
• when Bus receives the request, it locks the message
• after processing -> call CompleteAsync
• some error occur -> call AbandonAsync

5. Security:

- Using Shared Access Signature

• With Azure Portal -> use can define Share Access Policies for Namespaces, queues, topics, and their subscriptions
• There are three policy rules:
• Send
• Listen
• Manage
• SAS can be applied on the namespace, entity (queue, topic), HTTP level, or  AMQP level
• Use SAS Authorization
• Connection string contains a rule name (SharedAccessKeyName) and rule key (SharedAccessKey) => when we pass it to any constructor or factory,  the SAS token provider is automatically created and populated.
• Application usecase: => avoid use default Share Access Signature
• Grant role/claims for the client as their responsibility

References:

• https://docs.microsoft.com/en-us/azure/service-bus-messaging/service-bus-sas
• https://docs.microsoft.com/en-us/azure/service-bus-messaging/service-bus-queues-topics-subscriptions