Wcf architecture overview

WCF Architecture Overview

Sunday, December 16, 2012 Arbind

WCF Service
A service exposes endpoints

(Endpoint: a port to communicate with outside world)

Sunday, December 16, 2012
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A Client
Exchanges messages with one or more Endpoints.

May also expose an Endpoint to receive Messages from a Service in a duplex
message exchange pattern.

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Endpoint: Has
1. An Address
2. A Binding
3. A Contract

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Address:

A network location where the Endpoint resides.

Represented by an EndpointAddress Class

EndpointAddress is a URI, a collection of AddressHeader and identity

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Bindings: Has
1. A name
2. A namespace
3. A collection of binding elements

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Collection of binding elements:

Each binding elements describe how to communicate with the end point

1. TcpTransportBindingElement indicates that the Endpoint will
communicate with the world using TCP as the transport protocol.

2. ReliableSessionBindingElement indicates that the Endpoint
uses reliable messaging to provide message delivery assurances.

3. SecurityBindingElement indicates that the Endpoint uses SOAP
message security.

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Contracts:

Refers to the collection of operations which specify what endpoint will
communicate to out side world

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ContractDescription class is used to describe WCF Contracts
and their operations.

Each Contract Operation have OperationDescriptions and

each operationDescription have MessageDescription

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Duplex Contract: Defines two Logical Operations

1. A set that the Service exposes for the Client to call

2. A set that the Client exposes for the Service to call

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Contract: Has
1. Name
2. Namespace
3. Identity

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Contract:

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Behaviors:

Are types which modifies services or client functionalities

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ServiceBehavior is a type which implements
IServiceBehavior and applies to service

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ChannelBehavior is a type which implements
IChannelBehavior and applies to client

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Service and Channel Descriptions
The ServiceDescription class describes a WCF Service including the
Endpoints exposed by the Service, the Behaviors applied to the
Service, and the type (a class) that implements the Service.

ServiceDescription is used to create metadata, code/config, and
channels.

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Behavior:

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ChannelDescription describes a WCF Client's Channel to a
specific Endpoint

ServiceDescription can have multiple endpoint but
ChannelDescription have only one endpoint

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WCF Runtime:

The set of objects responsible for sending and receiving messages

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Message:

The unit of data exchange between a Client and an Endpoint

A message should be of SOAP message type and can be serialized
using the WCF binary format, text XML, or any other custom
format.

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Channels:

Channels are the core abstraction for sending Messages to and
receiving Messages from an Endpoint.

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Two Category of channel:

1. Transport Channels handle sending or receiving opaque octet
streams using some form of transport protocol such as TCP, UDP,
or MSMQ.

2. Protocol Channels, implement a SOAP-based protocol by
processing and possibly modifying messages.

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Procedure to define WCF Service
Step1: Defining and Implementing a Contract
using System.ServiceModel;

[ServiceContract]
public interface IMath
{
[OperationContract]
int Add(int x, int y);
}

Step2: Define a service class
This contract (interface IMath) is implemented to a class which becomes a
service class

public class MathService : IMath
{
public int Add(int x, int y)
{
return x + y;
}
}

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Step3: Defining Endpoints and Starting the Service
(endpoint can be defined in code or in config)

In Code:
public class WCFServiceApp
{
public void DefineEndpointImperatively()
{
//create a service host for MathService
ServiceHost sh = new ServiceHost(typeof(MathService));
//use the AddEndpoint helper method to
//create the ServiceEndpoint and add it
//to the ServiceDescription
sh.AddServiceEndpoint( typeof(IMath),
//contract type new WSHttpBinding(),
//one of the built-in bindings "http://localhost/MathService/Ep1");
//the endpoint's address
//create and open the service runtime
sh.Open();
}
public void DefineEndpointInConfig()
{
//create a service host for MathService
ServiceHost sh = new ServiceHost (typeof(MathService));
//create and open the service runtime
sh.Open();
}
}
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Endpoint in config file:

<configuration
xmlns="http://schemas.microsoft.com/.NetConfiguration/v2.0">
<system.serviceModel>
<services>

<service type="MathService">

<endpoint address="http://localhost/MathService/Ep1"
binding="wsHttpBinding" contract="IMath"/>
</service>
</services>
</system.serviceModel>
</configuration>

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Step4: Sending Messages to the Endpoint
using System.ServiceModel;
//this contract is generated by svcutil.exe
//from the service's metadata
public interface IMath
{
[OperationContract]
public int Add(int x, int y)
{
return x + y;
}
}
//this class is generated by svcutil.exe
//from the service's metadata
//generated config is not shown here
public class MathProxy : IMath
{ ... }

Continue……….

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In the following code first way to send the message to endpoint is like
SendMessageToEndpoint part. This hides the channel creation which is happening
behind the scene
Second way (SendMessageToEndpointUsingChannel) does it explicitly.

public class WCFClientApp
{
public void SendMessageToEndpoint()
{
//this uses a proxy class that was
//created by svcutil.exe from the service's metadata
MathProxy proxy = new MathProxy();
int result = proxy.Add(35, 7);
}
public void SendMessageToEndpointUsingChannel()
{
//this uses ChannelFactory to create the channel
//you must specify the address, the binding and
//the contract type (IMath)
ChannelFactory<IMath> factory=new ChannelFactory<IMath>( new WSHttpBinding(), new
EndpointAddress("http://localhost/MathService/Ep1"));
IMath channel=factory.CreateChannel();
int result=channel.Add(35,7);
factory.Close();
}
}

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Step5: Defining custom behavior
We need to implement IServiceBehavior for service and IChannelBehavior for
client

All behaviors can be applied imperatively by adding an instance of the
behavior to the ServiceDescription (or the ChannelDescription on the client
side).

ServiceHost sh = new ServiceHost(typeof(MathService));
sh.AddServiceEndpoint( typeof(IMath), new WSHttpBinding(),
"http://localhost/MathService/Ep1");
//Add the behavior imperatively
// InspectorBehavior is a custom behavior
InspectorBehavior behavior = new InspectorBehavior();
sh.Description.Behaviors.Add(behavior);
sh.Open();

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Secure Hosting and Deployment of WCF Services

Service host is a execution environment for service code

Service has to be hosted before deployment

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Why host is required?

 Provide security context for the execution of WCF service
 Providing a mechanism to configure the WCF service
 Providing a mechanism to monitor the statistics and health of WCF
service
 Provide rapid fail protection and tools for WCF service
management

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Type of host
1. Managed Application / Self Host
2. Managed Windows Service
3. IIS
4. WAS

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Criteria for Choosing a WCF Service Host

Consider following things before coming to conclusion

A. Target Deployment Platform
B. Protocol to be supported by the service

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Example:

If service needed to support HTTP, TCP, MSMQ and Named Pipe and
platform is Windows longhorn server – IIS 7.0 with WAS should
be used
If service needed to support HTTP and platform is Windows server
2003 – IIS 6.0 should be used
if TCP, MSMQ and Named Pipe required to be supported and
platform is Windows server 2003 - Managed Windows Service can
be used
If service need to support HTTP, TCP, MSMQ and Named Pipe
protocols on Windows Vista – IIS 7.0 along with WAS should be
used
On Windows XP, IIS 5.1 should be used if supported protocol is HTTP
and Windows service can be used for TCP, MSMQ and Named Pipe

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How to select host?

Managed Application / Self Host

Any .NET managed application can host a WCF service by creating an instance
of ServiceHost Class

ServiceHost Class is a member of System.ServiceModel namespace

(Hosting a Service in managed application is also called Self Hosting)

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Point to note: Self host does not provide features like message
based activation, mechanism to monitor service health or service
host resources or recycling of the service host process upon
detection of error conditions.

And so: This is useful in development environment but not in
production environment

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In Self Hosting, the Service Host has to be instantiated at the time of
the managed application startup and closed before the managed
application shutdown.

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The security context in Self Host is the identity under which the
managed application runs

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A WCF Service hosted in a managed application can be exposed over
TCP, HTTP, HTTPS, Named Pipe and MSMQ protocols.

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Code sample for creating a Service Host in
managed application

Using(ServiceHost serviceHost = new ServiceHost(typeof(CalculatorService)))
{
//Open the Service Host to start receiving messages
serviceHost.Open();
// The service is now ready to accept requests
…..
…..
// Close the ServiceHost to shutdown the service.
serviceHost.Close();
}

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The base address and the endpoints for the service host have to be configured in the
<services> sub section of the <system.serviceModel> section of the App.Config as
shown below:
<services>
<service
name="SecureHosting.Samples.CalculatorService"
behaviorConfiguration="CalculatorServiceBehavior">
<host>
<baseAddresses>
<add baseAddress="http://localhost:9000/SecureHostingSamples/service"/>
</baseAddresses>
</host>
<endpoint address=""
binding="wsHttpBinding"
contract="SecureHosting.Samples.ICalculator" />
<endpoint address="mex"
binding="mexHttpBinding"
contract="IMetadataExchange" />
</service>
</services>

<behaviors>
<serviceBehaviors>
<behavior name="CalculatorServiceBehavior">
<serviceMetadata httpGetEnabled="True"/>
<serviceDebug includeExceptionDetailInFaults="True" />
</behavior>
</serviceBehaviors>
</behaviors>


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Base Address and endpoint can also be configured
programmatically instead of configuring in App.Config file

// Create a ServiceHost for the CalculatorService type.
using (ServiceHost serviceHost =
new ServiceHost(typeof(CalculatorService),new
Uri("http://localhost:9000/SecureHostingSamples/service")))
{

//Configure the service with an end point
serviceHost.AddServiceEndpoint(typeof(ICalculator),
new WSHttpBinding(), "");
// Open the ServiceHost to start receiving messages
serviceHost.Open();
….
….
….

//Close the service host to shutdown the service
serviceHost.Close ();
}

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Managed Window Service
(A Window Service running under managed environment)
Service can be installed using Installutil tool.
The service can be exposed to HTTP, TCP, MSMQ and Named Pipe protocol

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The window service which host the service inherits from the
ServiceBase class and also implements contract

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Windows Service provides the facility to manage the lifecycle of the
service via the Service Control Manager (SCM) console

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Windows Service Host does not provide a message based activation

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Window service leverages the OnStart event to create service host
and host closes on OnStop event.

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Security context can be configured using Installer Class with the help
of ServiceProcessInstaller.

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Sample Code to create Managed Window Service
public class CalculatorService : ServiceBase, ICalculator
{
public ServiceHost serviceHost = null;

public static void Main()
{
ServiceBase.Run(new CalculatorService());
}

public CalculatorService()
{
ServiceName = "WCFWindowsCalculatorService";
}

//Start the Windows service.
protected override void OnStart(string[] args)
{
if (serviceHost != null)
{
}
// Create a ServiceHost for the Service
serviceHost = new ServiceHost(typeof(CalculatorService));

// Start Listening for the Messages
serviceHost.Open();
}

//Stop the Windows Service
protected override void OnStop()
{
if (serviceHost != null)
{
serviceHost = null;
}
}
}

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IIS
Allows the Services to be hosted in the App Domains inside the ASP.NET
worker process
Supported IIS: 5.1, 6.0, 7.0 8.0(BETA)
(Only Http and Https can be handled)

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IIS handles the service request in the same way as it handles web
request

Supports message based activation and service instance is created
only after receiving the first message.

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The security context for the WCF Service hosted inside the ASP.NET
worker process is provided by the service account under which the
worker process runs.

(Knowledge Sharing)
WHAT WILL BE THE SECURITY TO BE IMPLEMENTED?

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Hosting a service in IIS requires .SVC file to be created

If required a Custom Service Host we can create it using
System.ServiceModel.Activation.ServiceHostFactory Class

(Virtual applications are created and DLLs and sources are deployed to the
physical path associated with the virtual application)

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The configuration for the service endpoints has to be defined in the
Web.Config

The .SVC file should contain code like:

<%@ServiceHost language=c# Debug="true" Service="
SecureHosting.Samples.CalculatorService" %>

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Web.Config for IIS Host:

<services>
<service name="SecureHosting.Samples.CalculatorService"
behaviorConfiguration="CalculatorServiceBehavior">

<endpoint address=""
binding="wsHttpBinding"
contract="SecureHosting.Samples.ICalculator" />
<endpoint address="mex"
binding="mexHttpBinding"
contract="IMetadataExchange" />
</service>
</services>

<!--For debugging purposes set the includeExceptionDetailInFaults attribute to true--
>
<behaviors>
<serviceBehaviors>
<behavior name="CalculatorServiceBehavior">
<serviceMetadata httpGetEnabled="True"/>
<serviceDebug includeExceptionDetailInFaults="True" />
</behavior>
</serviceBehaviors>
</behaviors>

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WAS (Windows Activation Service)

WAS enables IIS 7.0 to leverage message based activation for
protocols such as TCP, MSMQ and Named Pipes in addition to the
HTTP protocol

Available with Windows Vista and Windows Longhorn Server

Service deployment process for IIS 7.0/WAS is same as discussed
earlier for IIS host

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Note:
1. web sites need to be configured via the APPCMD utility to support
non HTTP protocols

2. To do this command shell must be started in “Run as
Administrator” mode

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Command to run:

%windir%system32inetsrvappcmd.exe set site "Default Web Site"
-+bindings.[protocol='net.tcp',bindingInformation='808:*'] FOR
TCP

-+bindings.[protocol='net.msmq',bindingInformation='*'] FOR
MSMQ

-+bindings.[protocol='net.pipe',bindingInformation='*'] FOR
NAMED PIPE

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After running the command APPCMD updates configuration file for WAS
ApplicationHost.Config
<system.applicationHost>
<sites>
<site name="Default Web Site" id="1">
<bindings>
<binding protocol="http"
bindingInformation="*:80:" />
<binding protocol="net.pipe"
bindingInformation="*" />
<binding protocol="net.tcp"
bindingInformation="808:*" />
<binding protocol="net.msmq"
bindingInformation="*" />
</bindings>
</site>
</sites>
</system.applicationHost>

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To enable the TCP protocol (in addition to the HTTP protocol) for the
“SecureHostingSamples” application, the following command should be run
from an administrator shell:

%windir%system32inetsrvappcmd.exe set app "Default Web
Site/securehostingsamples" /enabledProtocols:http,net.tcp

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Selecting Binding:
Criteria to select Bindings:
1. Consider the deployment environment whether it is for Internet, Intranet,
Federated Environment, Windows only or a Heterogeneous Environment
2. Security to be implemented
3. Performance Issues

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A WCF service can be assigned:
1. Transport level security,
2. Message level security or
3. A combination of transport and message level security.

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A service can be defined with an authentication mode of
1. None,
2. Username,
3. Windows,
4. Certificates and
5. IssuedToken.

Authentication process between the client and the service includes the
authentication of service to the client as well as the authentication of the
client to the service.

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Deploying a WCF Service over Windows Only Intranet
In Windows only Intranet, if all the service clients are WCF clients, the
service can be deployed using NetTCPBinding and transport level security
to achieve maximum performance.

(NetTCPBinding by default uses transport level security along with TCP
channel and binary message encoding)

ClientCredentialType is set to Windows to enable Windows Authentication

Code Sample:

<bindings>
<netTcpBinding>
<binding name="Binding1">
<security mode="Transport" />
<transport
clientCredentialType="Windows" protectionLevel="EncryptAndSign"/>
</security>
</binding>
</netTcpBinding>
</bindings>

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Interoperability with web services

The WCF service can be configured to use BasicHttpBinding with transport
level security.
HTTP/GET metadata should be enabled for the service in the service behavior
section.

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Deploying a WCF Service over Internet or in a Heterogeneous Environment
(needs to potentially interact with the clients on non-windows platforms)

--BasicHttpBinding or WSHttpBinding can be used depending upon the level of
conformance required with the commonly used security standards
If interoperability is required with web service only BasicHttpBinding should be
used.

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To support SOAP Message Security UserName Token Profile version 1.0, the
WCF service should be configured with BasicHttpBinding with security
mode of TransportWithMessageCredential and client credential type of
UserName.

Example:

<basicHttpBinding>
<security mode="TransportWithMessageCredential">
<message clientCredentialType="UserName" />
</security>
</binding>
</basicHttpBinding>

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Deployment in Federated Environment
WCF Service client obtains a security token from Security Token Service (STS)
which is trusted by WCF Service

WCF Service should be configured for WSFederatedHttpBinding

The security token also contains the address of the endpoint to retrieve
metadata of STS

the certificate used by STS for signing the security token should be added to
the list of known certificates in the service credential section.

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<bindings>
<wsFederationHttpBinding>
<security mode ="Message">
<message issuedKeyType ="SymmetricKey" issuedTokenType ="http://docs.oasis-open.org/wss/oasis-
wss-saml-token-profile-1.1#SAMLV1.1" >
<issuerMetadata address ="http://localhost:8888/sts/mex" >
<identity>
<certificateReference storeLocation ="CurrentUser"
storeName="TrustedPeople"
x509FindType ="FindBySubjectDistinguishedName"
findValue ="CN=STS" />
</identity>
</issuerMetadata>
</message>
</security>
</binding>
</wsFederationHttpBinding>
</bindings>
<behaviors>
<serviceBehaviors>
<behavior name ="ServiceBehaviour" >
<serviceCredentials>
<issuedTokenAuthentication>
<knownCertificates>
<add storeLocation ="LocalMachine"
storeName="TrustedPeople"
x509FindType="FindBySubjectDistinguishedName"
findValue="CN=STS" />
</knownCertificates>
</issuedTokenAuthentication>
<serviceCertificate storeLocation ="LocalMachine"
storeName ="My"
x509FindType ="FindBySubjectDistinguishedName"
findValue ="CN=localhost"/>
</serviceCredentials>
</behavior>
</serviceBehaviors>
</behaviors>

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Assignment For All

Create a WCF service to convert
Fahrenheit to Celsius and vice versa and
to be hosted in IIS

If done: mail it on
arbindkumar_tiwari@satyam.com

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Wcf architecture overview

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