Service Bus provides a multi-tenant service for connecting applications through the cloud.

Within a namespace, you can use one or more instances of four different communication mechanisms, each of which connects applications in a different way. The choices are:

• Queues, which allow one-directional communication. Each queue acts as an intermediary (sometimes called a broker) that stores sent messages until they are received. Each message is received by a single recipient.
• Topics, which provide one-directional communication using subscriptions -a single topic can have multiple subscriptions. Like a queue, a topic acts as a broker, but each subscription can optionally use a filter to receive only messages that match specific criteria.
• Relays, which provide bi-directional communication. Unlike queues and topics, a relay doesn't store in-flight messages-it's not a broker. Instead, it just passes them on to the destination application.
• Event Hubs, which provide event and telemetry ingress to the cloud at massive scale, with low latency and high reliability.

When you create a queue, topic, relay, or Event Hub, you give it a name. Combined with whatever you called your namespace, this name creates a unique identifier for the object. Applications can provide this name to Service Bus, then use that queue, topic, relay, or Event Hub to communicate with one another.

To use any of these objects, Windows applications can use Windows Communication Foundation (WCF). For queues, topics, and Event Hubs Windows applications can also use Service Bus-defined messaging APIs. To make these objects easier to use from non-Windows applications, Microsoft provides SDKs for Java, Node.js, and other languages. You can also access queues, topics, and Event Hubs using REST APIs over HTTP.

It's important to understand that even though Service Bus itself runs in the cloud (that is, in Microsoft's Azure datacenters), applications that use it can run anywhere. You can use Service Bus to connect applications running on Azure, for example, or applications running inside your own datacenter. You can also use it to connect an application running on Azure or another cloud platform with an on-premises application or with tablets and phones. It's even possible to connect household appliances, sensors, and other devices to a central application or to one other. Service Bus is a generic communication mechanism in the cloud that's accessible from pretty much anywhere. How you use it depends on what your applications need to do.

27. How Service Bus Notification (including Hub) works, and what are main benefits of using the Service?

Smartphones and tablets have the ability to "notify" users when an event has occurred. In Windows Store applications, the notification can result in a toast: a modeless window appears, with a sound, to signal a new push. On Apple iOS devices, the push similarly interrupts with a dialog box, requesting the user to view or close the notification. Clicking View opens the application that is receiving the message.

Push notifications help mobile devices display fresh information while remaining energy-efficient. Push notifications are a vital component for consumer apps, where they are used to increase app engagement and usage. Notifications are also useful to enterprises, when up-to-date information increases employee responsiveness to business events.

Push notifications are delivered through platform-specific infrastructures called Platform Notification Systems (PNS). A PNS offers barebones functions (that is, no support for broadcast, personalization) and have no common interface. For instance, in order to send a notification to a Windows Store app, a developer must contact the WNS (Windows Notification Service), to send a notification to an iOS device, the same developer has to contact APNS (Apple Push Notification Service), and send the message a second time.

At a high level, though, all platform notification systems follow the same pattern:

1. The client app contacts the PNS to retrieve its handle. The handle type depends on the system. For WNS, it is a URI or "notification channel." For APNS, it is a token.
2. The client app stores this handle in the app back-end for later usage. For WNS, the back-end is typically a cloud service. For Apple, the system is called a provider.
3. To send a push notification, the app back-end contacts the PNS using the handle to target a specific client app instance.
4. The PNS forwards the notification to the device specified by the handle.

28. What is used in HDInsight Service for Big Data processing and how the Distributed Architecture looks?

Дата добавления: 2015-10-24