Developing Solutions for Microsoft Azure (AZ-204) Practice Exam

Which feature of Azure Service Bus ensures a first-in, first-out (FIFO) guarantee?

1. Transactions

2. Scheduled delivery

3. Message sessions

4. Dead-lettering

The correct answer is: Message sessions

Azure Service Bus utilizes message sessions to ensure first-in, first-out (FIFO) delivery of messages. When messages are sent with a session ID, the Service Bus groups them into a session so that all messages within that session are processed in the order they were received. This is particularly important for applications that need to maintain a strict order of operations, such as financial transactions or task orchestration, where the sequence of messages is crucial to correct system behavior. By using message sessions, a consumer can lock a session and receive all messages in that session in the order they were sent. This capability is key for scenarios that cannot tolerate out-of-order processing, offering a significant advantage over other methods that do not guarantee order. While transactions can help in ensuring atomicity during message processing, they do not inherently provide FIFO ordering for messages. Scheduled delivery allows sending messages at a later time but doesn't affect the order of processing. Dead-lettering is a mechanism to handle messages that cannot be delivered or processed successfully and does not have a role in maintaining message order.