Enterprise Messaging

Azure Service Bus is a fully managed enterprise message broker with message queues and publish-subscribe topics.

1. Queues vs Topics

Queues: Used for Point-to-Point communication. One sender, one receiver.
Topics/Subscriptions: Used for Pub/Sub. One sender, many receivers. Every 'Subscription' can have its own filters, so a 'Shipping' service only sees messages where Action == "Ship".

2. Enterprise Features

Azure Service Bus is much more powerful than simple storage queues. It supports **Transactions** (send 5 messages as an atomic unit), **Sessions** (guaranteed order for related messages), and **Scheduled Delivery** (send a message 2 hours from now).

3. Architect Insight

Q: "Should I use Service Bus or Storage Queues?"

Architect Answer: "Use **Storage Queues** if you need a simple, cheap buffer for massive amounts of small messages (80KB limit). Use **Service Bus** for everything else. It has a higher message size limit (up to 100MB in Premium), supports ordering, transactions, and provided a much more robust 'At-Least-Once' or 'Exactly-Once' delivery guarantee."