These questions are taken from .NET interview question book written by Shivprasadkoirala you can know more about the book from here http://www.flipkart.com/net-interview-questions-6th/p/itmdyuqzdqx8cvqx
What is WCF instancing?
WCF Instancing controls the instancing behavior of the service. In short it controls the scope of the service instance created.
What are the different modes available?
Three modes – Per Call, Per Instance and Single
Which one is the default one?
Can you explain all three modes in single sentence?
Per Call – One instance will be created per request.
Per Session – One instance will be created per session.
Single – Only one instance will exists throughout.
What do you mean by per request and per session?
Every invocation to one operation (method in programming word which is decorated with operation contract attribute) is considered as one new request.
Per Session means one client session usually considered on the basis of lifetime of object of proxy class created (unless and until Operation Context is used with IsInitiating and IsTerminating)
Is it possible to force a developer to configure only session full endpoints?
Yes, for that we will use SessionMode property with ServiceContract Attribute.
Recently one of our friends who went for TCS Mumbai interview was asked question around WCF one way binding. Below is a video created by www.questpond.com which explains the same in more detail