WCF Interview Questions and Answer

WCF Interview Questions and Answers

Q1. What is WCF?

WCF stands for Windows Communication Foundation. It is a Software development kit for developing services on Windows. WCF is introduced in .NET 3.0. in the System.ServiceModel namespace. WCF is based on basic concepts of Service oriented architecture (SOA)

Q2. What is endpoint in WCF service?

The endpoint is an Interface which defines how a client will communicate with the service. It consists of three main points: Address,Binding and Contract.

Q3. Explain Address,Binding and contract for a WCF Service?

Address:Address defines where the service resides.

Binding:Binding defines how to communicate with the service.

Contract:Contract defines what is done by the service.

Q4. What are the various address format in WCF?

a)HTTP Address Format:--> http://localhost:

b)TCP Address Format:--> net.tcp://localhost:

c)MSMQ Address Format:--> net.msmq://localhost:

Q5. What are the types of binding available in WCF?

A binding is identified by the transport it supports and the encoding it uses. Transport may be HTTP,TCP etc and encoding may be text,binary etc. The popular types of binding may be as below:

a)BasicHttpBinding

b)NetTcpBinding

c)WSHttpBinding

d)NetMsmqBinding

Q6. What are the types of contract available in WCF?

The main contracts are:

a)Service Contract:Describes what operations the client can perform.

b)Operation Contract : defines the method inside Interface of Service.

c)Data Contract:Defines what data types are passed

d)Message Contract:Defines wheather a service can interact directly with messages

Q7. What are the various ways of hosting a WCF Service?

a)IIS b)Self Hosting c)WAS (Windows Activation Service)

Q8. WWhat is the proxy for WCF Service?

A proxy is a class by which a service client can Interact with the service.

By the use of proxy in the client application we are able to call the different methods exposed by the service

Q9. How can we create Proxy for the WCF Service?

We can create proxy using the tool svcutil.exe after creating the service.

We can use the following command at command line.

svcutil.exe *.wsdl *.xsd /language:C# /out:SampleProxy.cs /config:app.config

Q10.What is the difference between WCF Service and Web Service?

a)WCF Service supports both http and tcp protocol while webservice supports only http protocol.

b)WCF Service is more flexible than web service.

Q11.What is DataContract and ServiceContract?Explain

Data represented by creating DataContract which expose the

data which will be transefered /consumend from the serive

to its clients.

Q12.What is .NET 3.0?

In one simple equation .NET 3.0 = .NET 2.0 + Windows Communication Foundation + Windows

Presentation Foundation + Windows Workflow Foundation + Windows Card Space.

Q13.What is WCF?

Windows Communication Foundation (WCF) is an SDK for developing and deploying services on Windows. WCF provides a runtime environment for services, enabling you to expose CLR types as services, and to consume other services as CLR types.

First let us give a short answer to this: - “WCF (Indigo was the code name for WCF) is a

unification of .NET framework communication technologies

“.WCF is a unification technology,

Q14.which unites the following technologies:-

• NET remoting

• MSMQ

• Web services

• COM+.

Q15.What was the code name for WCF?

The code name of WCF was Indigo .

WCF is a unification of .NET framework communication technologies which unites the following technologies:-

1.Web services

2.MSMQ

3.NET remoting

4.COM+

Q16.What are the main components of WCF?

The main components of WCF are

1. Service class

2. Hosting environment

3. End point

Q17.Where we can host WCF services?

Every WCF services must be hosted somewhere. There are three ways of hosting WCF services.

They are

1. IIS

2. Self Hosting

3. WAS (Windows Activation Service)

Q18.What is service and client in perspective of data communication?

A service is a unit of functionality exposed to the world.

The client of a service is merely the party consuming the service.

Q19.What are different elements of WCF Srevices Client configuration file?

WCF Services client configuration file contains endpoint, address, binding and contract.

A sample client config file looks like

Q20.What is endpoint in WCF?

Every service must have Address that defines where the service resides, Contract that defines what the service does and a Binding that defines how to communicate with the service. In WCF the relationship between Address, Contract and Binding is called Endpoint.

Q21.What are ends, contract, address, and bindings?

The above terminologies are the core on which SOA stands. Every service must expose one or more ends by which the service can be available to the client. End consists of three important things where, what and how:-

• Contract (What)

Contract is an agreement between two or more parties. It defines the protocol how client should communicate with your service. Technically, it describes parameters and return values for a method.

• Address (Where)

An Address indicates where we can find this service. Address is a URL, which points to the

location of the service.

• Binding (How)

Bindings determine how this end can be accessed. It determines how communications is done.

For instance, you expose your service, which can be accessed using SOAP over HTTP or

BINARY over TCP. So for each of these communications medium two bindings will be created.

Below figure, show the three main components of end. You can see the stock ticker

is the service

class, which has an end hosted on http://www.soa.com with HTTP and TCP binding support and using

Stock Ticker interface type.

Q22.What is binding and how many types of bindings are there in WCF?

A binding defines how an endpoint communicates to the world. A binding defines the transport (such as HTTP or TCP) and the encoding being used (such as text or binary). A binding can contain binding elements that specify details like the security mechanisms used to secure messages, or the message pattern used by an endpoint.

Q23.WCF supports nine types of bindings?

Basic binding

Offered by the BasicHttpBinding class, this is designed to expose a WCF service as a legacy ASMX web service, so that old clients can work with new services. When used by the client, this binding enables new WCF clients to work with old ASMX services.

This binding is used when we need to use SOAP over HTTP. This binding

can also be configured to be used as HTTPS. It can be also configured to send data in plain text or in optimized form like MTOM.

TCP binding

Offered by the NetTcpBinding class, this uses TCP for cross-machine communication on the intranet. It supports a variety of features, including reliability, transactions, and security, and is optimized for WCF-to-WCF communication. As a result, it requires both the client and the service to use WCF.

This binding sends binary-encoded SOAP, including support for reliable

message transfer, security, and transactions, directly over TCP. The biggest disadvantage of

NetTcpBinding is that both server and client should be also made in .NET language.

Peer network binding

Offered by the NetPeerTcpBinding class, this uses peer networking as a transport. The peer network-enabled client and services all subscribe to the same grid and broadcast messages to it.

IPC binding

Offered by the NetNamedPipeBinding class, this uses named pipes as a transport for same-machine communication. It is the most secure binding since it cannot accept calls from outside the machine and it supports a variety of features similar to the TCP binding.

Web Service (WS) binding

Offered by the WSHttpBinding class, this uses HTTP or HTTPS for transport, and is designed to offer a variety of features such as reliability, transactions, and security over the Internet.

It is same like BasicHttpBinding. In short, it uses SOAP over HTTP. But with

it also supports reliable message transfer, security and transaction. WS-Reliable Messaging,

security with WS-Security, and transactions with WS-Atomic Transaction supports reliable

message.

Federated WS binding

Offered by the WSFederationHttpBinding class, this is a specialization of the WS binding, offering support for federated security.

Duplex WS binding

Offered by the WSDualHttpBinding class, this is similar to the WS binding except it also supports bidirectional communication from the service to the client.

MSMQ binding

Offered by the NetMsmqBinding class, this uses MSMQ for transport and is designed to offer support for disconnected queued calls.

MSMQ integration binding

Offered by the MsmqIntegrationBinding class, this converts WCF messages to and from MSMQ messages, and is designed to interoperate with legacy MSMQ clients.

This binding sends binary-encoded SOAP over MSMQ. This binding can

only be used for WCF-to-WCF communication.

Q24.What are the different concurreny modes available in WCF?

1. Single

2. Reentrant

3. Multiple

Q25.Are WCF services protected from concurrent access by default?

Yes, WCF services are protected from concurrent access by default, as the concurrency mode of a WCF service is set to Single by default.

Q26.Explain Single Concurrency Mode?

In a Single concurrency mode only one request is processed by the same service instance. A lock is acquired while a request is processed by a service instance. Other threads, if any, are queued, until they timeout. Once the lock is released when the current request completes, next thread in the queue can then access the objects.

Q27.What effect does Single concurreny mode setting have on PerCall, PerSession and Singleton services?

PerCall services and Single Concurreny mode : A new service instance is allocated for each thread. Here, concurrency is not an issue and Single mode setting has no impact on the throughput and concurrent calls can be processed.

Q28.PerSession services and Single Concurreny mode : Service instances are protected against multithreaded clients. Single mode impacts throughput of single client but multiple clients can get through and concurrent calls can be processed.

Q29.Singleton services and Single Concurreny mode : Service instances are protected against any concurrent calls. Single concurrency mode impacts throughput of singleton. Multiple threads and clients cannot get through and no concurrent calls can be processed.

Q30.Explain Reentrant Concurrency Mode?

Reentrant concurrency mode is useful when services issue callbacks to clients, If callback operations are not one-way. Services release the acquired lock upon exit to make the callback and another thread is able to acquire the lock. In this case, return from callback will queue.

Q31.What effect does Reentrant concurreny mode setting have on PerCall, PerSession and Singleton services?

PerCall services and Reentrant Concurreny mode : In a case where PerCall services may need reentrancy, if we set the concurrency mode to Single, deadlock is guaranteed, where as if it is In Reentrant mode, we will have no problem.

Q32.PerSession services and Reentrant Concurreny mode : PerSession services allow a multithreaded client to access the service instance

Q33.Singleton services and Reentrant Concurreny mode : Singleton services allow any threads to access the service instance

Q34.What is the effect of Multiple concurrency mode on PerSession services with multithreaded clients?

PerSession services with multithreaded clients can have increased throughput, with Multiple concurrency mode, as no locks are acquired when requests are being processed by a service instance. However, care should be taken to protect shared resources.

Q35.What are different .NET multithreading techniques available to protect a shared resource?

1. Monitor

2. Mutex

3. Semaphore

4. ReadWriterLock

5. Interlocked

Q36.What are the factors that can influence overall throughput for a service, when multiple concurrency mode is enabled?

1. Instancing mode

2. Concurrency mode

3. Throttling behavior

Q37.What is ServiceThrottleBehavior?

ServiceThrottleBehavior provides several settings for throughput control, as shown below.

MaxConcurrentCalls: Maximum concurrent requests allowed. The default is 16 .

MaxConcurrentInstances: Maximum concurrent service instances allowed . The default is int.MaxValue.

MaxConcurrentSessions: Maximum concurrent active sessions. This includes transport, reliable, secure, and application sessions. The default is 10.