Hedronite · Cert Lesson · Cert-Prep / Microsoft · Thu 2026-10-01

AZ-900 — Service Bus, Event Hubs, and Storage Queues

Three Azure services move messages. Only one of them is a full broker.

Lesson Class: Cert-Prep (AZ-900 Messaging)
Cert Target: AZ-900 Azure Fundamentals
Paired Ops: Rust Service Bus queue DLQ census
Paired Dev: Rust trait objects for delivery policies
Grounding: az-900 README · learn.microsoft.com Service Bus / Event Hubs / Storage Queues
Service Bus
Broker: queues, topics, sessions, DLQ.
Event Hubs
Ingestion pipe: partitions, consumer groups.
Storage Queues
Simple durable queue; no broker extras.
Name the broker, the log, and the simple queue as three different words.

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Three Azure services move messages. Only one of them is a full broker. Name the shape before you pick the SKU.

§I — Frame: fifth Microsoft visit, messaging door

08-11 opened the hierarchy. Management groups, subscriptions, resource groups, RBAC, Policy, locks, composite SLA. Leave it.

08-23 opened identity. Entra ID, AuthN before AuthZ, Conditional Access. Leave it.

09-04 opened storage redundancy and access tiers. Leave the copy-that-is-not-a-backup trap alone today.

09-19 opened networking. VNet, NSG, peering, VPN. Leave it.

Today the Cloud rotation counter reads 15. Fifteen mod 4 is 3. Seat 3 is AZ-900 again. Ops in this trio walks Service Bus queues with a Rust census. Cert stays at fundamentals: which messaging word means which thing.

§II — Three claims

Claim one. Service Bus is the broker. az-900 README: Azure Service Bus transfers data and state asynchronously between applications. Queues give competing consumers one message each. Topics plus subscriptions give fan-out: each subscription gets its own copy. Sessions, transactions, and dead-letter sub-queues belong here. Peek-lock settlement and maxDeliveryCount are Service Bus ideas. If the exam names "enterprise messaging" or "publish/subscribe with filters," the answer is Service Bus.

Claim two. Event Hubs is the ingestion pipe. Event Hubs is built for high-throughput event and telemetry streams. Producers append into partitions. Consumers read with consumer groups and advance offsets. It is closer to a log than to a command queue. You do not use Event Hubs when one worker must exclusively process an order and dead-letter a poison message after ten tries. You use it when many readers need a replayable stream of events.

Claim three. Storage Queues are the simple durable queue. A Storage Queue lives inside a storage account. Messages are small (documentation ceiling 64 KB). The API is deliberately thin: put, get, delete, update visibility timeout. There are no topics, no sessions, no transactions, and no Service Bus-style dead-letter sub-queue. Pick Storage Queues when the app needs a cheap backlog between two components and does not need broker features.

§III — Contrast table

NeedPrefer
Competing consumers + dead-letter + sessionsService Bus queue
Fan-out with per-subscriber filtersService Bus topic + subscriptions
Telemetry / clickstream / replay by offsetEvent Hubs
Tiny durable buffer in a storage accountStorage Queues
"Is this a broker or a log?"Broker = Service Bus; log/stream = Event Hubs

Named trap: Queue Word Collision. The word "queue" appears in Service Bus and in Storage. They are not the same product. Service Bus queues carry broker semantics. Storage Queues carry blob-adjacent durability and a small API. Answering "Storage Queue" to a question that mentions topics, sessions, or dead-letter is the classic miss.

§IV — Worked scenario

A checkout service must hand each order to exactly one fulfillment worker, retry a few times, then park poison orders for a human. A second analytics pipeline wants every order event for a dashboard, without competing with fulfillment.

Fundamentals answer:

  1. Fulfillment: Service Bus queue (competing consumers, delivery count, dead-letter).
  2. Analytics: Service Bus topic with a subscription (fan-out), or Event Hubs if the volume is a continuous telemetry firehose and replay-by-offset matters more than per-message settlement.

Storage Queues are the wrong tool once dead-letter and fan-out enter the sentence.

§V — Five drills

  1. Exam says "publish/subscribe with subscriptions." Which service?
  2. Exam says "partitions and consumer groups for telemetry." Which service?
  3. Exam says "64 KB messages in a storage account." Which service?
  4. Does Storage Queues provide a built-in dead-letter sub-queue like Service Bus?
  5. Peek-lock and maxDeliveryCount belong to which of the three?

Answers: (1) Service Bus topic/subscriptions (2) Event Hubs (3) Storage Queues (4) No (5) Service Bus.

§VI — Close instruction

Write three flash cards, one per service, each with one sentence for "what it is" and one sentence for "when it is the wrong tool." Recite them without looking at the table. If you swap Service Bus and Storage Queues under the word "queue," rewrite the Queue Word Collision card until you stop.

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