Azure Queue Storage vs Azure Service Bus Queue vs Azure Service Bus Topic

What is Azure Queue Storage?

Queue storage is a service that uses Azure Storage to store large numbers of messages that can be securely accessed from anywhere in the world using a simple REST-based interface. Queues can contain millions of messages, limited only by the capacity of the storage account that owns it.

What is Azure Service Bus Queues?

Service Bus is a message broker system intended for enterprise applications. These apps often utilize multiple communication protocols, have different data contracts, higher security requirements, and can include both cloud and on-premises services. Service Bus is built on top of a dedicated messaging infrastructure designed for exactly these scenarios.

Both of these services are based on the idea of a "queue" which holds sent messages until the target is ready to receive them.

What are Azure Service Bus Topics?

Azure Service Bus topics are like queues, but can have multiple subscribers. When a message is sent to a topic instead of a queue multiple components can be triggered to do their work. Imagine in a music sharing application, a user listening to a song. The mobile app might send a message to the "Listened" topic. That topic will have a subscription for "UpdateUserListenHistory" and a different subscription for "UpdateArtistsFanList". Each of those functions is handled by a different component that receives its own copy of the message.

Internally, topics use queues. When you post to a topic, the message is copied and dropped into the queue for each subscription. The queue means that the message copy will stay around to be processed by each subscription branch even if the component processing that subscription is too busy to keep up.

Which one to choose?

Choose Service Bus Topics if

• you need multiple receivers to handle each message

Choose Service Bus queues if:

• You need an At-Most-Once delivery guarantee.
• You need a FIFO guarantee.
• You need to group messages into transactions.
• You want to receive messages without polling the queue.
• You need to provide a role-based access model to the queues.
• You need to handle messages larger than 64 KB but less than 256 KB.
• Your queue size will not grow larger than 80 GB.
• You would like to be able to publish and consume batches of messages.

Queue storage isn't quite as feature-rich, but if you don't need any of those features, it can be a simpler choice. In addition, it's the best solution if your app has any of the following requirements.

Choose Queue storage if:

• You need an audit trail of all messages that pass through the queue.
• You expect the queue to exceed 80 GB in size.
• You want to track progress for processing a message inside of the queue.

A queue is a simple, temporary storage location for messages sent between the components of a distributed application. Use a queue to organize messages and gracefully handle unpredictable surges in demand.

Use Storage queues when you want a simple and easy-to-code queue system. For more advanced needs, use Service Bus queues. If you have multiple destinations for a single message, but need queue-like behavior, use topics.