What is the difference between Azure Service Bus and Storage Queues?

Both are Azure queueing services but solve different problems.

Azure Storage Queues

• Simple FIFO-ish queue (no strict ordering guarantees)
• Up to 80 GB total / 64 KB per message
• HTTP polling API
• ~$0.0005 per 10K operations
• No publish-subscribe, no transactions

var queue = new QueueClient(conn, "orders");
await queue.SendMessageAsync(JsonSerializer.Serialize(order));

await foreach (var msg in queue.ReceiveMessagesAsync()) {
    Process(msg);
    await queue.DeleteMessageAsync(msg.MessageId, msg.PopReceipt);
}

Good for: simple work queues, decoupling a background worker from an HTTP API, "I just need messages out of process".

Azure Service Bus

• Enterprise messaging with AMQP support
• Topics + subscriptions (pub/sub)
• Sessions (FIFO per-key)
• Transactions, dead-letter, scheduled delivery
• Up to 80 GB total / 256 KB per message (1 MB Premium)
• ~$0.05 per million operations (Basic tier)

var sender = client.CreateSender("orders");
var msg = new ServiceBusMessage(JsonSerializer.Serialize(order)) {
    SessionId = order.CustomerId.ToString(),
    ScheduledEnqueueTime = DateTimeOffset.Now.AddMinutes(5)
};
await sender.SendMessageAsync(msg);

Good for: enterprise integration, saga choreography, ordered processing per partition, fan-out via topics.

Decision table:

Need	Storage Queue	Service Bus
Cheap, simple	✓	✗
Pub/sub (topics)	✗	✓
Strict FIFO per key	✗	✓ (sessions)
Transactions	✗	✓
Dead-letter	manual	built-in
Scheduled delivery	✗	✓
Message size > 64 KB	✗	✓
AMQP integration	✗	✓

Rule of thumb: start with Storage Queues. Upgrade to Service Bus when you need pub/sub, sessions, or transactional messaging. The Service Bus tier is overkill for a simple work queue but indispensable when business processes span multiple services.