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📬 Messaging & NServiceBus

Azure Essentials (nice-to-have)

Service Bus vs Storage Queues, Functions triggers.

Listed as "gradite" (nice-to-have), so depth matters less than being able to hold a coherent conversation.

Azure Service Bus — Microsoft's managed enterprise message broker: queues (point-to-point, Command-like) and topics/subscriptions (pub/sub, Event-like) — maps directly onto the Command/Event distinction from NServiceBus. Supports sessions (ordered processing per session ID, same idea as partitioning by OrderId above), and dead-lettering built in.

Storage Queues — simpler, cheaper, part of a Storage Account — basic FIFO-ish queueing without Service Bus's richer features (no topics/pub-sub, simpler retry semantics). Reach for Service Bus when you need pub/sub, sessions, or more sophisticated delivery guarantees; Storage Queues for simple, high-volume, low-complexity queueing.

Azure Functions — serverless compute, commonly triggered by a Service Bus/Storage Queue message arriving — a natural fit for lightweight message handlers that don't need a whole always-on service host.

Flashcards (2)

How does Azure Service Bus map onto the Command vs Event distinction?
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Service Bus queues are point-to-point (one consumer per message) — Command-like. Service Bus topics + subscriptions are pub/sub (multiple independent subscribers each get their own copy) — Event-like.
When would you reach for Azure Service Bus over Storage Queues?
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When you need pub/sub (topics/subscriptions), ordered processing via sessions, or richer built-in dead-lettering/delivery guarantees. Storage Queues suit simple, high-volume, low-complexity point-to-point queueing where those features aren't needed.