.Net Remoting

OverView:

Distributed application is a set of components distributed across network and work as if all the components are there on the same computer. These components based technologies can be developed using DCOM, CORBA, RMI etc. These technologies are good for intranet environment. Microsoft has provided suitable framework for developing distributed application through .Net Remoting and Web Services. Remoting.net allows components to interact across application domains, processes, and machine boundaries. It enables your applications to take advantage of remote resources in a networked environment. Web Services are best suited when clients outside the firewall calling components on the server over the Internet.Remoting.Net is the best solution when clients and components are inside the firewall. It requires the client to be built using .NET which means it can’t work in heterogeneous environments. .Net Remoting uses channels (HTTP and TCP channels) to transport messages to and from remotable objects. The HTTP channel uses the SOAP protocol to transport messages which means all messages are serialized to XML. The TCP channel uses a binary stream to transport the messages. .Net Remoting supports two activation modes: Singleton and SingleCall. Singleton mode allows only one instance of an object at any time which means all requests are serviced by the single instance. You can maintain state across each request using this mode. SingleCall Mode creates a new instance of the object for each client request and are stateless. .NET Remoting when hosted with IIS, can use all the security features of ASP.NET. But you need to implement your own security features for the application if channel is hosted in the process other than aspnet_wp.exe.

When to use .Net Remoting over Web services.

Net Remoting provides distributed solution for a corporate use. So, if you need distributed environment to be implemented for internal use, .Net remoting is the best choice. If you require a faster distributed solution, .Net Remoting with TCP protocal using binary format is faster than Web services. .Net Remoting is better solution when large transfer of data is required.

What is .Net Remoting?
.Net Remoting enables communication between applications across separate domains or networks. .Net objects are exposed to remote processes to have interprocess communication. With remoting, we can use TCP or HTTP communications protocols on any port. We can use text or binary formatting. .Net Remoting supports server activated (single call and singleton) as well as client activated objects.

Describe the .Net Remoting Architecture.
.Net Remoing allows communication between server and client objects. To facilitate this, when new instance of remote object is created in the client application, the client receives reference (called proxy) to the server object. This proxy object contains references to all the methods and properties of the server object. When the client object calls any method (the call actually on proxy object), which resolves the references and invokes server object, receives the result and pass on to the client application.

What are the remotable and non-remotable objects in .Net Remoting.
The remotable objects are the objects which can be distributed accross domains, can be used with domain. The non-remotable objects are the objects which can't be distributed accross domains. In distributed system, if an object is very big, we can make it non-remotable object.
Describe the type of remotable objects in .Net Remoting.
Marshal-by-value-objects - When client calls a method on marshal-by-value-object, the remoting system creates a copy of this object and passes the copy to the client application domain. The copy hence received can handle any method call in client domain. Using Marshal-by-value-object reduces resource consuming trip across network. Marshal-by-reference-object - When client calls a method on Marshal by reference object, the remoting system create proxy object in the caller application that contains the reference of all method and properties of the object.

What are the types of activation modes in .Net remoting?
Server Activation Mode: In this mode, objects are created on the server when we call a method in the server class and not when we create instance using new. In this type of scenario, the client is always connected with server but the services are activated only when we call the method of the server class. We can create server activated object as a Singleton or SingleCall object. If we create server object as singleton, a single instance will manage all the clients. If we create server object as singlecall, the remoting system creates object each time a client method invokes a remote object.
Client Activation Mode: This object gets created when we create instance using new keyword. In this mode, client application domain defines the lifetimes of client activated objects. The client domain defines the lifetimes of client-activated objects. They use lifetime leases to determine the duration of their existence and after the lifetime expires, the object is marked for GC.

Describe the term Channel in .Net Remoting.
In .Net Remoting, an application use Channel to send message to another application which is runing in different domain or process. Before sending message, Channel converts message into appropriate format like XML or binary format. The channel that carries message(Mashalled parameter) can use protocal like TCP and HTTP. Channel can be HTTPChannel and TCPChannel. The HTTPChannel use soapFormatter to serialize messages into the XML format using SOAP protocal. Using SOAP method allows the client to call method on the remote object that might not be using .Net framework. The TCPChannel use binaryFormatter to serialize message into binary stream.

How does .Net Remoting works?
Remoting.Net allows components to interact across application domains, processes, and machine boundaries, thus allows applications to access remote resources in a networked environment. The interaction of components is made possible through proxy in remoting architecture. When a client calls the remote method, it’s the proxy that receives the call. The proxy then encodes the message using formatter. The messages are then sent over the channel to the server process where listening channel receives the call and passes it to the remoting system. The requested method is then invoked and results are returned back to the client.
.Net Remoting provides an infrastructure where objects of different AppDomains can interact. A client interacts with server object using .Net Remoting architecture. An object interacts with other objects outside AppDomains using proxy since the objects can't access directly anything outside AppDomain.
Point to be noted.A remote object is implemented by inheriting MarshalByRefObject class.A client has to obtain proxy activating a remote object by calling CreateInstance, GetObject, or new.Local objects can be passed as parameters when making remote calls. Local objects are passed by value in a remote call.The object passed as parameter in a remote call must be serialized.
Activation ModelYou need to activate remote object before use. There are two activation modes in .Net RemotingServer Activation In this mode, objects are created automatically when a client attempts to access the object. The object doesn't get created when you use new keyword to create instance of the server class. Client ActivationIn this mode, objects are created when you use new keyword to create instance of the server class.
A server object is created and deployed on the network that serves client requests. The server objects have to be registered with the CLR before it can be accessed by client. The details that have to be provided to the CLR are
Name of the assembly that should be loaded to activate the objectThe namespace and type name of the objectThe name of the endpoint where the object can be accessed The channels to be used by client to communicate have to be registered.The registered channels then start listening for clients to connect.
Once a remote object has been deployed, clients can connect and invoke methods on the server object.
In order to access remote object, the client first activates the object by calling new, GetObject, or CreateInstance. On activation request, a proxy is created to represent the remote object. The client message in the serialized form is transported to the server. The type of serialization depends on the channel. For example, when the HTTP channel is used, all messages are serialized to XML and transported over SOAP. On the other hand, TCP uses binary serialization.
On the server side, the requested method is then invoked and results are packaged in a message and returned back by to the client. If the target object is of type SingleCall, it will automatically be garbage collected after the call completes.

Approaches to access server objects in Remoting.Net
First one to have copy of server object on the client machine and accessing local copy of object to call method. This method is good suited when the object is not very big not having too many methods. Copying big object is wastage of client resources which includes network resources and processing time. The second approach is to create a proxy object that returns reference of all the methods and properties of server object in the client domain. The proxy acts as local object, fake server object on the client machine. Any method call from the client will be served by proxy which in turn access server domain to get response from server object. This approach is good when the object is big with many methods.

.Net Remoting Interview

DCOM vs .Net Remoting
.Net Remoting is the successor of Distributed component object Model(DCOM). Both these technology are introduced by Microsoft that enable inter-process communication across application domains. DCOM was very successful technology. But it is never treated as best technology for inter-process communication because of lack of its support for interoperability across platform.
.Net Remoting is a new technology that ship with .Net Framework. It has all those features which are missing in DCOM. There are other pain involve with DCOM such as difficult to control format or channels, message trace is painful, change in configuration setting such as channels or port is not easy. DCOM is hard to learn and complicated to deploy and to maintain.

Differences between these two technologies are as follows.
DCOM technology is based on the COM architecture whereas .NET Remoting is primarily based on .NET Frameworks.DCOM is based on proprietary binary protocol which is not supported by all object model, thus has big drawbacks in the internet world.
DCOM is based on RPC protocol whereas .Net Remoting can use TCP or HTTP protocol which is stardard protocal in the market.
DCOM is not firewall friendly, can't choose port. .Net Remoting, on the other hand, works easily across firewalls.
.Net Remoting supports cross platform communication which is not possible with DCOM (only for windows platform).
Components created DCOM involves complex deployment in windows registries whereas .Net Remoting involves easy deployment using either xml based configuration file or programmatically in the code.
DCOM uses windows security features whereas .Net Remoting can use security features of IIS if hosted with ASP.NET. .Net Remoting, if hosted other than ASP worker process, allows to create own security mechanism for the application.
In DCOM, server is started by Service Control Manager (SCM) upon receiving the activation request from the client whereas in .Net Remoting, IIS is responsible to start server service. If not hosted with IIS then client request will fail if the Remoting server is not already started.
DCOM manages remote object lifetime by frequent pinging of clients whereas .Net Remoting has more efficient leasing mechanisms to maintain object lifetime.

Define windows process:
A process is an instance of a running application.Each process is allocated its own block of available RAM space.No process can access another process code or data. If the process crashes, it dies alone without taking the entire OS or a bunch of other applications down.

Define channels in .NET Remoting
Channels represent the objects that transfer the other serialized objects from one application domain to another and from one computer to another, as well as one process to another on the same box. A channel must exist before an object can be transferred.

What security means available for .NET Remoting in System.Runtime.Remoting?
None. Security should be taken care of at the application level. Cryptography and other security techniques can be applied at application or server level.

What is a formatter in .Net Remoting?
A formatter is an object that is responsible for encoding and serializing data into messages on one end, and deserializing and decoding messages into data on the other end.

.NET Remoting and Web services.
Use remoting for more efficient exchange of information when you control both ends of the application. Use Web services for open-protocol-based information exchange when you are just a client or a server with the other end belonging to someone else.

Name the distributed systems available apart from .Net Remoting.
Distributed Computing Environment/Remote Procedure Calls (DEC/RPC),Microsoft Distributed Component Object Model (DCOM), Common Object Request Broker Architecture (CORBA), and Java Remote Method Invocation (RMI).

How do you implement distributed applications in .NET?
.NET Remoting and ASP.NET Web Services.Classes for the same are in System.Runtime.Remoting and System.Web.Services.

Define proxy in .NET Remoting.
Its a fake copy of the server object that resides on the client side and behaves as if it was the server. It handles the communication between real server object and the client object. This process is also known as marshaling.

Define remotable objects in .NET Remoting.

Remotable objects are the objects that can be marshaled across the application domains.You can marshal by value, where a copy of the object is created and then passed to the receiver. You can also marshal by reference, where just a reference to an existing object is passed.

Define SingleCall activation mode in .Net Remoting.
If the server object is instantiated for responding to just one single request, the request should be made in SingleCall mode.

Define Singleton activation mode in .Net Remoting.
A single object is instantiated regardless of the number of clients accessing it. Lifetime of this object is determined by lifetime lease.

Define the lease of the object.
By implementing ILease interface when writing the class code.

.NET Remoting versus Distributed COM
.NET Remoting is the successor of DCOM. Microsoft DCOM is a solution for distributed object and very good in terms of performance when components are in the same network. But its drawbacks in the internet connected world are visible. It uses proprietary binary protocol which is not supported by other object models, thus can't support interoperability across platform. .NET Remoting uses TCP or HTTP protocol that is supported by most of the object models. This allows .NET Remoting to be adaptable to the network environment in which it is being used.

Advantage of Remoting over Web Services
.NET Remoting allows objects to interact that can be hosted in different application domain within the same process or different process. The objects can also interact over intranet or internet. It supports many different protocols unlike Web Services that works over SOAP/HTTP protocol. .Net Remoting can work on TCP protocol that provides speed benefit from its counterpart. Being tied up with IIS, .Net Web service can only work with producer /consumer model whereas .Net Remoting can share objects from any type of application. .Net Remoting being part of .Net Framework support full .Net type system and can expose any object to the client. .Net Web Service supports on those types that can be expressed with XSD.

When should we choose .Net Remoting over .Net Web Services?
.Net Remoting provides distributed solution for a corporate use. So, if you need distributed environment to be implemented for internal use, .Net remoting is the best choice.
If you require a faster distributed solution, .Net Remoting with TCP protocal using binary format is faster than Web services. .Net Remoting is better solution when large transfer of data is required. Web Services provide an open-protocol-based exchange of information. Web Services are best when you need to communicate with an external organization or non .NET technology.

What are the ways to configure Remoting objects before client can use them?
There are two ways that the remoting objects can be configured. They can be configured by calling configuration methods inside the application. .Net Framework allows configuring objects also by adding configuration section in the application configuration file or machine.config file. Application-level XML settings take precedence over machine.config. When you apply any change in the configuration section, you don’t need to recompile the code. On the other hand, any change in the setting applied programmatically would require recompiling the code.

Define Delegates.
A delegate acts like a strongly type function pointer. Delegates can invoke the methods that they reference without making explicit calls to those methods. It is type safe since it holds reference of only those methods that match its signature. Unlike other classes, the delegate class has a signature. Delegates are used to implement event programming model in .NET application. Delegates enable the methods that listen for an event, to be abstract.

Define Events.
Events are one of the members of the class. When any noteworthy activity occurs in the application, an event is raised which sends out the message to the other part of the application which handles the event. The event can carry arguments that contain information about the event. The method which handles the event must have the same signature as the event itself. Events are commonly used in the applications with graphical user interface elements such as buttons, textbox etc. An event is triggered when any action such as mouse click occurred in the interface element. The event-based programming model can be used in the non-GUI applications such as .NET Remoting application. An event in remoting.net occurs when the state of the application changes.

What is asynchronous programming?
.Net Remoting supports asynchronous programming. In this model, a call is made to a class method while the calling program continues to execute. This increase application speed as the application continues to execute without waiting for the called methods to finish execution.

When do we use delegates in your remoting applications?
You use delegates to implement callback functions, event programming, and asynchronous programming in your remoting applications. Events use delegates to enable callback functions to the client in remoting applications.

What are the ways to renew lifetime leases of objects?
A client can renew the lifetime lease of an object by calling the ILease.Renew method.

What are the types of remotable objects?
The two types of remotable objects are
Marshal-by-value objects - These objects are copied and passed by value out of the application domain. When client calls a method on marshal-by-value-object, the remoting system creates a copy of this object and passes the copy to the client application domain. The copy hence received can handle any method call in client domain. Using Marshal-by-value-object reduces resource consuming trip across network.
Marshal-by-reference objects - The clients that use these objects need a proxy to access the object remotely. When client calls a method on Marshal by reference object, the remoting system create proxy object in the caller application that contains the reference of all method and properties of the object.

What are the Security features in .Net Remoting.
.Net Remoting is integral part of .Net Framework, so it has access to all security features of Framework. If remoting objects are hosted using IIS, it leverages the entire authentication and authorization features that are available to Web based protocols. If hosted other than HTTP protocols over IIS, then you have the opportunity to create your own security infrastructure.

What are the information required to configure remote objects?
Following information to be provide to configure remote object.
Activation type for the remote object Channels URL of the remote object Type metadata of the remote object .

Explain Serialization Formatters in .NET Remoting.
In .Net Remoting, the objects are shared over distributed network. The objects are transmitted in serialized form. The objects are first serialized into message data before it is sent with the wire. On the other end of the wire, this serialized data is read and desterilized back to the actual object. This process of converting objects into message data is done by serialization formatters. .Net Remoting supports two formatters. SOAP FormatterBinary FormatterSOAP Formatter converts objects into XML string whereas Binary Formatter converts an object's state into a binary stream. The binary serialization formatter is slightly faster.

What are the requirements to enable remote components to interact each other?
To enable communication between objects across remoting boundaries, you need to have A server object to expose service A client that calls server object to consume service A message transmission protocol

Steps to publish an object outside the service domain.
To publish a service outside the service domain, you need to:
Identify the application domain that will host the service. Identify the activation model: server activation or client activation. Identify and create a channel and a port. Identify how the client application obtains the metadata information about the service.

Define Client Activated Objects (CAO).
Client-activated objects are objects whose lifetimes are controlled by the client, i.e. calling application domain. This mode works in similar fashion to the model where object is local to the client and referenced object's lifetime is controlled by the calling object. When instance of server object is created, object reference is obtained in the form of proxy.
In COM model, clients hold an object in memory by holding a reference to it. The object is released from the memory when the entire client releases the reference. But in .Net Remoting, client-activated objects use lifetime leases to determine how long they should continue to exist. When a client creates a remote object, it can specify a default length of time that the object should exist. If the remote object reaches its default lifetime limit, it contacts the client to ask whether it should continue to exist, and if so, for how much longer. If the client is not currently available, a default time is also specified for how long the server object should wait while trying to contact the client before marking itself for garbage collection. The client might even request an indefinite default lifetime. Client-activated instances serve only the client and the reference that was responsible for their creation.
To create an instance of a client-activated type, clients either configure their application programmatically or using a configuration file and call new, or they pass the remote object's configuration in a call to Activator.CreateInstance.

Explain Marshalling and its types in .Net Remoting.
Objects can't be transmitted as such over communication channel. The objects are packed into message buffer before transmitted. This process is called marshalling. There are two different ways to Marshal objects:
Marshal by Value: Server creates copy of the remoting object's state and passes it to the client. You need to implement your classes to have marshal by value features either by implementing ISerializable interface or using attribute. Here you need to copy whole object to the client which means with large size object, the communication overhead is significant.
Marshal by Reference: In this type proxy is created by the reference of the server objects. Class must extend the System.MarshalByRefObject to implement marshal by reference. Here, client keeps server object reference which means round trip to server with each method call.

Summary of .Net Remoting
.Net enables interaction between applications over distributed network.
To develop a Remoting application, you need to create client and server objects. You need to activate the objects and use reference of the server objects in client to communicate.
Channels allow application to send and receive messages using protocal like TCP or HTTP.
You can use delegates in Remoting application to implement event based programming and asynchronous programming.
Asynchronous programming in Remoting application helps to calls remote methods while client continues to execute other local method.
To host remote object, server needs some information about the objects.
The information can be provided programmatically in the code or can be loaded from configuration section of application configuration file or machine.config file.
Being part of .Net Framework, .Net Remoting can implement role based security. Moreover, it can leverage all security features of ASP.NET, if it hosted in ASP.NET.