# Sunday, November 02, 2008
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.NET Services is a block of functionality layered on top of the Azure platform. This project has had a couple of names in the past – BizTalk Services when it was an incubation project and then Zurich as it was productionized.


.NET Services consists of three services:

1)      Identity

2)      The Service Bus

3)      Workflow


Lets talk about identity first. Officially named the .NET Access Control Service, this provides you a Security Token Service (STS) that you can use to configure how different forms of authentication map into claims (it leverages the claims construct first surfaced in WCF and now wrapped up in Geneva). It supports user ids/passwords, Live ID, Certs and full blown federation using WS-Trust. It also supports rule based authorization against the claim sets.


The Service Bus is a component that allows you to both listen for and send messages into the “service bus”. More concretely it means that from inside my firewall I can listen to an internet based endpoint that others can send messages into. It supports both unicast and multicast. The plumbing is done by a bunch of new WCF Bindings (the word Relay in the binding indicates it is a Service Bus binding) although there an HTTP based API too. Sending messages to the internet is fairly obvious how that happens, its the listening that is more interesting. The preferred way is to use TCP (NetTcpRelayBinding) to connect. This parks a TCP session in the service bus which it then sends messages to you down. However they also support HTTP although the plumbing is a bit more complex. There they construct a Message Buffer that they send messages into then the HTTP relay listener polls it for messages. The message buffer is not a full blown queue although it does have some of the same characteristics of a queue. There is a very limited size and TTL for the messages in it. Over time they may turn it into a full blown queue but for the current CTP it is not.


So what’s the point of the Service Bus? It enables to be subscribe to internet based events (I find it hard to use the word “Cloud” ;-)) to allow loosely coupled systems over the web. It also allows the bridging of on-premises systems to web based ones through the firewall


Finally there is the .NET Workflow Service. This is WF in the Cloud (ok I don’t find it that hard). They provide a constrained set of activities (currently very constrained although they are committed to providing a much richer set. They provide HTTP Receive and Send and Service bus Send plus some flow control and some XPath ones that allow content based routing. You deploy your workflow into their infrastructure and can create instances of it waiting for messages to arrive and to route them, etc. With the toolset you basically get one-click deployment of XAML based workflows. They currently only support WF 3.5 although they will be rolling out WF 4.0 (which is hugely different from WF 3.5 – thats the subject of another post) in the near future.


So what does .NET Services give us? It provides a rich set of messaging infrastructure over and above that of Windows Azure Services

.NET | Azure | WCF | WF