AZ-900 Describe Azure architecture and services Practice Question
A company is designing a solution that requires guaranteed message delivery and exactly-once processing for financial transactions. Which Azure messaging service should they use?
⚠ Common exam trap
Candidates often confuse 'at-least-once' delivery (common in Queue Storage and Event Hubs) with 'exactly-once' processing, or they assume Event Grid's low-latency routing implies reliability guarantees, when in fact only Service Bus provides the necessary transactional and duplicate detection features for financial transactions.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Azure Service Bus
Azure Service Bus is the correct choice because it supports guaranteed message delivery through its 'Peek-Lock' and 'Scheduled Delivery' features, and it provides exactly-once processing via duplicate detection (based on the MessageId property) and transaction support (atomic operations across multiple entities). This makes it ideal for financial transactions where message loss or duplication is unacceptable.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Azure Queue Storage
Why it's wrong here
Azure Queue Storage is a simple, durable message queue built on Azure Storage, but it only offers at-least-once delivery with a visibility timeout for retries. If a message is processed but the delete call fails, it becomes visible again, creating duplicates; there is no session support to group related messages or maintain state, and there is no transaction scope that spans send/receive/complete operations. Consequently, it is not suitable for financial transactions that demand exactly-once or atomic processing.
- ✗
Azure Event Hubs
Why it's wrong here
Azure Event Hubs is designed as a high-throughput telemetry ingestion and event streaming platform, not as a transactional message broker. It provides at-least-once delivery via consumer groups and partition leases, but it lacks session-based ordering, per-message duplicate detection, and atomic transaction support between enqueue and processing actions. Therefore it cannot guarantee exactly-once processing or idempotent financial transactions.
- ✓
Azure Service Bus
Why this is correct
Azure Service Bus is a full-featured enterprise message broker with queues and topics that supports sessions and duplicate detection natively. Sessions enable FIFO and stateful message groups, while duplicate detection removes duplicated sends and receives within a deduplication window, together offering exactly-once processing semantics. Additionally, Service Bus supports atomic transactions that can batch send, receive, and complete operations against a queue, which is essential for reliable financial transaction workflows.
- ✗
Azure Event Grid
Why it's wrong here
Azure Event Grid is an event routing backbone that pushes discrete events to registered subscribers (Webhooks, Functions, Logic Apps) without tracking message state or providing delivery guarantees beyond at-least-once. It does not implement session grouping, duplicate detection, or transactional processing, and its reaction model is inherently stateless. As a result, it cannot provide the exactly-once and order-guaranteed semantics that financial transaction processing requires.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This AZ-900 practice question is part of Courseiva's free Microsoft certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the AZ-900 exam.