Azure Service Bus Queues

Azure Service Bus queues provide reliable, point-to-point message delivery between a sender and a receiver. They are the simplest messaging primitive in Service Bus and are ideal for decoupling services in distributed architectures. This lesson covers queue fundamentals, how messages flow through a queue, the receive modes, and practical considerations for building production systems.

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What Is a Service Bus Queue?

A Service Bus queue is a durable, brokered message store. Messages are sent to the queue by one or more producers and consumed by one or more competing consumers. The queue guarantees:

• Durability — messages are stored in the broker until a consumer acknowledges them
• FIFO ordering — messages are delivered in the order they were enqueued (first-in, first-out), though competing consumers can process them out of order unless sessions are used
• At-least-once delivery — every message is delivered to at least one consumer
• Load levelling — the queue absorbs traffic spikes so consumers can process at their own pace

Queue vs Storage Queue

Azure offers two queue services:

Feature	Service Bus Queue	Azure Storage Queue
Protocol	AMQP 1.0, HTTP	HTTP
Max message size	256 KB (Standard), 100 MB (Premium)	64 KB
Ordering	FIFO guaranteed	Best-effort
Delivery	At-least-once, at-most-once	At-least-once
Dead-lettering	Yes	No
Transactions	Yes	No
Max queue size	1 GB – 80 GB	500 TB

Use Service Bus queues when you need ordering, transactions, dead-lettering, or enterprise-grade reliability. Use Storage queues for simple, high-volume scenarios where individual message size is small and you do not need advanced features.

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Creating a Queue

Before you can send or receive messages, you need a Service Bus namespace — a container for queues, topics, and subscriptions.

Using the Azure CLI

# Create a resource group
az group create --name rg-messaging --location uksouth

# Create a Service Bus namespace (Standard tier)
az servicebus namespace create \
  --name sb-demo-ns \
  --resource-group rg-messaging \
  --sku Standard

# Create a queue
az servicebus queue create \
  --name orders \
  --namespace-name sb-demo-ns \
  --resource-group rg-messaging

Key Queue Properties

When creating a queue, you can configure:

Property	Description	Default
maxSizeInMegabytes	Maximum queue size (1024, 2048, 3072, 4096, 5120 MB for Standard)	1024 MB
defaultMessageTimeToLive	How long a message lives before expiring	14 days
lockDuration	How long a message is locked for a receiver in PeekLock mode	30 seconds
maxDeliveryCount	Number of delivery attempts before dead-lettering	10
requiresDuplicateDetection	Enable duplicate detection	false
deadLetteringOnMessageExpiration	Send expired messages to the dead-letter queue	false

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Sending Messages

Messages are sent to a queue using a sender client. Each message has a body (the payload) and optional properties (metadata).

import { ServiceBusClient } from '@azure/service-bus';

const client = new ServiceBusClient(connectionString);
const sender = client.createSender('orders');