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WCF Interview Questions and Answers

Updated Apr 30, 2025

1. What is WCF and what does WCF stand for?

WCF stands for Windows Communication Foundation. It is a framework developed by Microsoft for building service-oriented applications. It enables applications to be built as distributed and interoperable services that can communicate across different platforms and networks.

2. Which specifications does WCF follow?

WCF supports a variety of WS-* standards, including:

  • Messaging: WS-Addressing
  • Reliability: WS-ReliableMessaging
  • Security: WS-Security, WS-SecureConversation, WS-Trust
  • Transaction: WS-AtomicTransaction, WS-Coordination
  • Metadata: WS-MetadataExchange, WS-Policy

3. What are the main components of WCF?

  • Service Class: Contains the methods to be exposed.
  • Hosting Environment: Where the service runs (IIS, WAS, Windows Service, or self-hosted).
  • Endpoint: Defines how and where a service can be accessed.

4. How to create a WCF service?

  1. Open Visual Studio and create a new WCF Service Application.
  2. Define the service contract and implement it.
  3. Configure the service endpoints in the Web.config file.
  4. Host the service (IIS, self-hosting, etc.).
  5. Consume the service from a client application.

5. What is an endpoint in WCF?

An endpoint allows clients to communicate with the WCF service. It consists of:

  • Address: The location of the service.
  • Binding: Defines how to communicate with the service.
  • Contract: Describes the operations provided.
  • Behaviors: Optional settings for execution.

6. What is a service contract in WCF?

A service contract defines the operations that the service exposes. It is specified using the [ServiceContract] and [OperationContract] attributes and represents the public interface for client-service communication.

7. How to host WCF service in IIS?

  1. Create a WCF Service Application project in Visual Studio.
  2. Publish the project to a folder.
  3. Open IIS Manager and add a new website pointing to the published folder.
  4. Ensure .svc handler is configured.
  5. Browse the service URL to test.

8. What is metadata in WCF?

Metadata describes the capabilities of a WCF service, such as available methods and data types. It is exposed using the ServiceMetadata behavior and helps tools like "Add Service Reference" to generate proxy classes.

9. What is WCF RIA Services?

WCF RIA Services was a framework used with Silverlight to simplify n-tier application development by sharing code between client and server. It is now deprecated, as Silverlight is obsolete.

10. What are different bindings supported by WCF?

  • BasicHttpBinding
  • NetTcpBinding
  • NetNamedPipeBinding
  • WSHttpBinding
  • WSDualHttpBinding
  • NetMsmqBinding
  • NetPeerTcpBinding
  • WSFederationHttpBinding
  • MsmqIntegrationBinding

11. What is a proxy in WCF?

A proxy in WCF is a client-side class generated to communicate with the WCF service. It represents the service contract and handles communication, serialization, and deserialization. It can be auto-generated using tools like svcutil.exe.

12. Which transport schemas are supported by WCF?

  • HTTP/HTTPS
  • TCP
  • Named Pipes (IPC)
  • MSMQ
  • Peer-to-Peer Network

13. How to debug a WCF service?

  1. Set breakpoints in the service code.
  2. Attach the Visual Studio debugger to the running process (e.g., w3wp.exe for IIS).
  3. Invoke the service from a client.
  4. Check for exceptions or faults in service logs or the debugger.

14. What are message exchange patterns in WCF?

  • Request-Reply: Default pattern where the client waits for the response.
  • One-Way: Client sends a message without expecting a reply.
  • Duplex: Enables two-way communication using callbacks.

15. What is interoperability in WCF?

WCF supports interoperability by following WS-* standards and SOAP messaging. It can communicate with non-.NET platforms like Java or PHP, as long as the services follow the WS-I Basic Profile 1.1.

16. What is WebHttpBinding in WCF?

WebHttpBinding is used to create RESTful WCF services that communicate using HTTP requests and responses. It supports JSON and XML and does not follow SOAP or WS-* specifications by default.

17. What is throttling in WCF?

Throttling controls how many instances or calls a service can handle simultaneously. It is configured using serviceThrottling behavior and includes properties like:

  • maxConcurrentCalls
  • maxConcurrentInstances
  • maxConcurrentSessions

18. What are the different transaction isolation levels in WCF?

  • Read Uncommitted
  • Read Committed
  • Repeatable Read
  • Snapshot
  • Serializable

19. How to maintain security in WCF?

Security in WCF is achieved using:

  • Authentication: Verifying identity
  • Authorization: Granting access
  • Confidentiality: Encrypting data
  • Integrity: Ensuring data hasn't been altered

Security modes:

  • Transport security: Secures the transport channel (e.g., HTTPS)
  • Message security: Secures the message using encryption/signing

20. How to hide methods in WCF?

To hide methods from the client, avoid marking them with [OperationContract] or use the Name attribute to expose a different method name. This allows internal methods to remain hidden while exposing a public-facing API.

What are the different ways to host a WCF service?

WCF services can be hosted in:

  • Self-hosting: In a console or Windows service application.
  • IIS hosting: Suitable for HTTP-based services with automatic process recycling.
  • WAS hosting: Supports advanced protocols like TCP and named pipes.

What are behaviors in WCF?

Behaviors are customizations that affect runtime operations of WCF services. Examples include:

  • Service behaviors: Modify service-wide settings (e.g., metadata publishing).
  • Endpoint behaviors: Alter endpoint behavior (e.g., enabling REST via WebHttpBehavior).
  • Operation behaviors: Affect individual method execution (e.g., serialization options).

What is Instance Management in WCF?

WCF provides three instance management modes:

  • Per-Call: New service instance per request.
  • Per-Session: One instance for a client's session.
  • Single: One instance for all requests (singleton behavior).

What is the difference between BasicHttpBinding and WSHttpBinding?

Feature BasicHttpBinding WSHttpBinding
Protocol SOAP 1.1 SOAP 1.2 + WS-*
Security Basic/Transport WS-Security
Transactions No Yes
Interoperability High Lower

What is DataContract and DataMember in WCF?

DataContract marks a class as serializable for WCF. DataMember marks fields/properties to include in serialization.

[DataContract]
public class Employee {
  [DataMember]
  public string Name { get; set; }
}

How is versioning handled in WCF?

WCF versioning can be managed using:

  • New service interfaces (e.g., IMyServiceV2)
  • Optional fields in DataContracts
  • Maintaining backward compatibility

What are the advantages of using WCF over traditional Web Services (ASMX)?

  • Unified API for various protocols
  • Built-in support for security, transactions, and reliability
  • Extensible via custom behaviors and bindings

What is a ChannelFactory in WCF?

ChannelFactory allows creating WCF client channels programmatically without configuration files:

ChannelFactory<IMyService> factory = new ChannelFactory<IMyService>("myEndpoint");
IMyService proxy = factory.CreateChannel();

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