At the moment there are a number of Azure messaging services available.
- Storage Queue
- Service Bus Queue
- Service Bus Topic
- Event Hubs
- Event Grid
- IoT Hub
This article gives you a general overview.
Azure Queue storage is a service for storing large numbers of messages that can be accessed from anywhere in the world via authenticated calls using HTTP or HTTPS. A single queue message can be up to 64 KB in size, and a queue can contain millions of messages, up to the total capacity limit of a storage account. The maximum time that a message can remain in the queue is 7 days.
Common uses of Queue storage include:
- Creating a backlog of work to process asynchronously
- Passing messages from an Azure web role to an Azure worker role
Service Bus Queue
Messages are sent to and received from queues. Queues enable you to store messages until the receiving application is available to receive and process them.
Messages in queues are ordered and timestamped on arrival. Once accepted, the message is held safely in redundant storage. Messages are delivered in pull mode, which delivers messages on request.
Service Bus Topic
In contrast to queues, in which each message is processed by a single consumer, topics and subscriptions provide a one-to-many form of communication, in a publish/subscribe pattern. Useful for scaling to large numbers of recipients, each published message is made available to each subscription registered with the topic. Messages are sent to a topic and delivered to one or more associated subscriptions, depending on filter rules that can be set on a per-subscription basis. The subscriptions can use additional filters to restrict the messages that they want to receive. Messages are sent to a topic in the same way they are sent to a queue, but messages are not received from the topic directly. Instead, they are received from subscriptions. A topic subscription resembles a virtual queue that receives copies of the messages that are sent to the topic. Messages are received from a subscription identically to the way they are received from a queue.
By way of comparison, the message-sending functionality of a queue maps directly to a topic and its message-receiving functionality maps to a subscription. Among other things, this feature means that subscriptions support the same patterns described earlier in this section with regard to queues: competing consumer, temporal decoupling, load levelling, and load balancing.
Azure Event Hubs is a Big Data streaming platform and event ingestion service, capable of receiving and processing millions of events per second. Event Hubs can process and store events, data, or telemetry produced by distributed software and devices. Data sent to an event hub can be transformed and stored using any real-time analytics provider or batching/storage adapters.
Event Hubs is used in some of the following common scenarios:
- Anomaly detection (fraud/outliers)
- Application logging
- Analytics pipelines, such as clickstreams
- Live dashboarding
- Archiving data
- Transaction processing
- User telemetry processing
- Device telemetry streaming
Azure Event Grid allows you to easily build applications with event-based architectures. You select the Azure resource you would like to subscribe to, and give the event handler or WebHook endpoint to send the event to. Event Grid has built-in support for events coming from Azure services, like storage blobs and resource groups. Event Grid also has custom support for application and third-party events, using custom topics and custom webhooks.
You can use filters to route specific events to different endpoints, multicast to multiple endpoints, and make sure your events are reliably delivered. Event Grid also has built in support for custom and third-party events.
IoT Hub is a managed service, hosted in the cloud, that acts as a central message hub for bi-directional communication between your IoT application and the devices it manages. You can use Azure IoT Hub to build IoT solutions with reliable and secure communications between millions of IoT devices and a cloud-hosted solution backend. You can connect virtually any device to IoT Hub.
IoT Hub supports communications both from the device to the cloud and from the cloud to the device. IoT Hub supports multiple messaging patterns such as device-to-cloud telemetry, file upload from devices, and request-reply methods to control your devices from the cloud. IoT Hub monitoring helps you maintain the health of your solution by tracking events such as device creation, device failures, and device connections.
IoT Hub’s capabilities help you build scalable, full-featured IoT solutions such as managing industrial equipment used in manufacturing, tracking valuable assets in healthcare, and monitoring office building usage.
What to use when?
Azure provides myriad options to perform messaging and decouple applications. Which one should you use, and when?
|Use for decoupling||X||X||X||X||X|
|Use for publish/subscribe||X||X|
|Max message size||64K||64K||256KB||1MB||256 KB|1 MB||64KB|