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Exposing FTP servers using the Windows Azure appfabric service bus

, 14 Mar 2013 CC (ASA 3U)
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Exposing FTP servers using the Windows Azure appfabric service bus.

Introduction

As the different cloud-computing infrastructures are getting stabilized, more and more applications are being deployed to these infrastructures. Among these applications, quite a considerable number of applications are being migrated from traditional deployment to cloud. But sometime due to certain constraints it may not be always possible to move an entire application to cloud but move only parts, for instance, move the presentation and business layer to cloud but the backend database remains on-premise.

In some of my blogs (ref- one and two), I have had presented different ways of how easily one may expose the on-premise database (i.e. the one within the corporate network behind the firewall) to the consumer application in the internet using the Azure building blocks. In this article, I will try to explain an approach of how easily one may even expose their existing on-premise FTP server across the corporate firewall to support some application which is probably moved to cloud or other external deployment (internet).

To achieve this, we will make use of the Azure appfabric Service bus to expose the file from the FTP server as WCF service end points. The WCF service can be deployed either on IIS or on any other hosting application like console application. But while using IIS we need to make sure to enable the auto-start for the WCF service otherwise the service would not be available by default for consumption by any client. For the steps to be followed to enable the auto-start, refer to this MSDN page, these steps will make sure to start the service deployed in IIS the moment the IIS is started, instead of waiting for the first service request to come in.

On a high level, the FTP server is basically a file repository and provides access to the files on need basis. So, we may develop a REST based WCF service layer which will expose some interface across appfabric service bus and internally it will access the on-premise FTP server to access the intended files.

Lets us now see how to achieve the above said implementation and expose the files from on-premise FTP server across the corporate firewall using the Windows Azure appfabric service bus.

Assumptions

The reader is aware of the following:

  • REST based WCF service implementation
  • Windows Azure AppFabric service bus and the related relay bindings
  • The mechanism to access the files in the FTP server

Steps to be followed

1. Service Implementation

If IIS is to be used for hosting the service, then create a project of type WCF Service Library. And if any other applications like console application is to be used for hosting then create a project of type Console Application.

a. Add the service contract to expose the REST interface

[ServiceContract]

public interface IExposeFTPContract

{

[OperationContract]

[WebGet(UriTemplate = "/{fileName}")]

Message GetFile(string fileName);

}

Where "Message" represents a unit of communication and has its definition in the namespace: System.ServiceModel.Channels.

b. Add the service interface definition

public class ExposeFTPContract: IExposeFTPContract

{

public Message GetFile(string fileName)

{

//read the file and return as Message object

//following Console.WriteLines provided for tracing the calls

Console.WriteLine("Accessed at- " + DateTime.Now.ToString());

Console.WriteLine("--------------------------------------------");

using (FileStream fileStream = File.Open(

<complete file path to a FTP server using the file name provided>,

FileMode.Open))

{

using (create some suitable reader using the fileStream, e.g. fileReader)

{

Message message = Message.CreateMessage(MessageVersion.None,"", fileReader);

using (MessageBuffer messageBuffer = message.CreateBufferedCopy(1000))

{

return messageBuffer.CreateMessage();

}

}

}

}

}

Here the goal is to provide an interface for accessing file from the FTP server. This is one of the ways to make the file accessible through service interface; I believe there are other better ways as well.

2. Service configuration

In the host configuration file, i.e., web.config if IIS is used and app.config if a console application is used, add the following configuration settings:

a. Add a service end point

<services>

<service name="namespace.ExposeFTPContract"

behaviorConfiguration="ExposeFTPServiceBehavior">

<endpoint behaviorConfiguration="webhttpSharedSecretClientCredentials"

contract=”namespace.IExposeFTPContract"

binding="webHttpRelayBinding" bindingConfiguration="webHttpRelayEndpointConfig" />

</service>

</services>

The appfabric namespace also needs to be provided so, in case the service is hosted in IIS, then add the attribute address="http://<appfabric namespace>.servicebus.windows.net/ to the "endpoint" above as:

<endpoint behaviorConfiguration="webhttpSharedSecretClientCredentials"

contract=”namespace.IExposeFTPContract"

binding="webHttpRelayBinding" bindingConfiguration="webHttpRelayEndpointConfig" address="http://<appfabric namespace>.servicebus.windows.net"/>

And if hosted using console application, then appfabric namespace could be provided during the host initiation (described later in section "3. Service Hosting").

b. Add service behavior

<serviceBehaviors>

<behavior name="ExposeFTPServiceBehavior">

<!-- To avoid disclosing metadata information, set the value

below to false and remove the metadata endpoint above before deployment -->

<serviceMetadata httpGetEnabled="true" />

<!-- To receive exception details in faults for debugging purposes,

set the value below to true. Set to false before deployment

to avoid disclosing exception information -->

<serviceDebug includeExceptionDetailInFaults="true" />

</behavior>

</serviceBehaviors>

c. Add end point behavior

This end point behavior serves the following purposes:

  • Exposes service interface as REST and
  • Provides credential to connect to the appfabric service bus and expose the service across the corporate firewall.

<endpointBehaviors>

<behavior name="webhttpSharedSecretClientCredentials">

<!—to provide credential to connect to the appfabric service bus-->

<transportClientEndpointBehavior credentialType="SharedSecret">

<clientCredentials>

<sharedSecret issuerName="appfabric issuer name e.g. owner" issuerSecret="appfabric secret key" />

</clientCredentials>

</transportClientEndpointBehavior>

<!—to expose service interface as REST-->

<webHttp/>

</behavior>

</endpointBehaviors>

Where, the issuer name and issuer secret are the ones available once the appfabric namespace is created using the Azure subscription.

d. Add WCF binding

The WCF binding- "webHttpRelayBinding" needs to be configured as this will establish a duplex communication channel with the appfabric service across the corporate firewall.

<bindings>

<webHttpRelayBinding>

<binding name="webHttpRelayEndpointConfig">

<security mode="None" relayClientAuthenticationType="None"/>

</binding>

</webHttpRelayBinding>

</bindings>

3. Service Hosting

In case the service is to be hosted in Console application then update "main" method in program.cs in the project with the following code:

try

{

Console.Title = "Expose Client FTP through appfabric Service Bus";

string serviceNamespaceDomain = appfabric namespace or could be read from the config settings;

Console.WriteLine("Service Namespace Domain : " + serviceNamespaceDomain);

Console.WriteLine("");

// create the service URI based on the appfabric namespace

Uri address = ServiceBusEnvironment.CreateServiceUri("http", serviceNamespaceDomain, "");

// create the service host reading the configuration

ServiceHost host = new ServiceHost(typeof(ExposeFTPContract), address);

Console.WriteLine("Starting service...");

// create the ServiceRegistrySettings behavior for the endpoint.

// This will make this service visible along with other services registerred

// to the same appfabric namespace in the atom feed if one tries to access

// the url- http://<appfabric namespace>.servicebus.windows.net

IEndpointBehavior serviceRegistrySettings = new ServiceRegistrySettings(DiscoveryType.Public);

foreach (ServiceEndpoint subscriberEndpoint in host.Description.Endpoints)

{

subscriberEndpoint.Behaviors.Add(serviceRegistrySettings);

}

// open the service

host.Open();

Console.WriteLine("Service started...");

Console.WriteLine("Service address: " + address);

Console.WriteLine("");

Console.WriteLine("FTP files may now be accessed as:");

Console.WriteLine(address + "<file name>");

Console.WriteLine("");

Console.WriteLine("Press [Enter] to exit");

Console.WriteLine("");

Console.WriteLine("--------------------------------------------");

Console.ReadLine();

// close the service

host.Close();

}

catch (Exception ex)

{

Console.WriteLine("Error: " + ex.Message);

}

If IIS is used to host, make sure the hosted service and the corresponding application pool is running.

Conclusion

Once the service is running, files from the on-premise FTP server can be accessed over the Windows Azure AppFabric URL such as: http://<appfabric_namespace>.servicebus.windows.net/<file_name>.

The code could be enhanced based on one’s need but this explains how easily one can expose on-premise FTP server for internet based consumer application using the Azure appfabric service.

License

This article, along with any associated source code and files, is licensed under The Creative Commons Attribution-Share Alike 3.0 Unported License

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About the Author

Rahul Bandopadhyaya
Architect Infosys Limited
India India
I am currently working as Technical Architect in Infosys Limited and My motto is "share the good knowledge so that my fellow colleague or those from the same profession may not face the same issue as I have had… enjoy coding and sharing knowledge"
 
"Disclaimer: Any views or opinions presented in this article are solely those of the author and do not represent those of Infosys Limited. Infosys Limited does not accept any liability in respect of any views or content present herein."

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