Web Dynpro Application in Cluster environment

[Former Member]

Hi all,

I have a doubt about WebDynpro application running on a clustered environment. The sceanrio is that a Web Dynpro Application is running on a clustered environment with say 2 servers. A user logs into the application and starts working on it. In between the server on which the application is running shut downs, due to some reason. As it was a cluster the other server will host the application.

But will the user needs to login again into the application?? I mean will his session end (untimely) when the first server shuts down.

Thanks and Regards,

Gaurav

[Former Member · Accepted solution]

Hi Gaurav,

Your Question: Now, client or user is finished with filling of the form and presses submit button. Will the application work normally?

As specified in the previous response: "If the Server crashes in between the HTTP request session then the request is assinged to the another server node to generate the response"

If the user finishes filling up of a form and clicks on Submit button then a request is generated now if even before the request gets completed the current server crashes then this request will be assigned to the next server node to complete the request and generate a response, the response here would be from successful save of data in the database. In that case the data will not be lost.

[Former Member]

Hi

http://help.sap.com/saphelp_nw04/helpdata/en/0d/a3bb3eff62847ae10000000a114084/frameset.htm

go through this link hope it will be use of it

Regards

Ruturaj

[Former Member]

Hi Gaurav,

Please refer to the following link, it contains a presentation and explains diagramatically J2EE server failover.

http://wendtstud1.hpi.uni-potsdam.de/sysmod-seminar/SS2005/presentations/02-Clustering-Concept_SAP_W... (SAP® Web AS)

[Former Member]

Hi Gaurav,

Yes, the currently running session will be taken care of by the another server node which is up and running.

Your question: Does this mean that the a session of WebDynpro application will continue to work or the changes are lost and the user needs to login again?

"The state of the session is maintained in the persistent storage after the last successfully ended request." Which means that for example a user was filling up a form and haven't saved the changes and the server crashes then the data on that form will be lost when the second server node starts processing the request. But if the user had saved the data before the server crashes that state of the session will be stored and the data of the form will be saved and user need not fill it up again. If the Server crashes in between the HTTP request session then the request is assinged to the another server node to generate the response. In none of the case user needs to login again.

Your question: Fundamentally the question is what WebDynpro uses behind the scenes for maintaining session?

It uses Java Serialization to serialize the HTTP Sessions

"Serialization involves saving the current state of an object to a stream, and restoring an equivalent object from that stream. The stream functions as a container for the object. The information stored in the container can later be used to construct an equivalent object containing the same data as the original."

Edited by: Aishwarya Sharma on Oct 7, 2008 8:07 AM

[Former Member]

Hi Aishwarya,

Thanks for your precise answer and links.

But i still have doubt, when you say that server stores the state which is saved on the last server request. Then the client who is filling a form does not really involve a server processing and say in between the server node which is actually handling the Web Dynpro application request goes off. And then another server node is assigned the job. Now, client or user is finished with filling of the form and presses submit button. Will the application work normally? If yes, then probably we donot loose any information in such an event.

Please, let me know if my understanding is incorrect.

Thanks & Regards,

Gaurav.

[Former Member]

Hi Gaurav,

When the server process that processes the HTTP request crashes the

dispatcher redirects the request to another server node. The new server process reads the information about the

requested session from the persistent storage that holds the state after the last successfully ended request and

continues processing the new request.

Please refer to the following link:

https://www.sdn.sap.com/irj/sdn/go/portal/prtroot/docs/library/uuid/e10b4b78-0801-0010-aaba-fb0a5f9c...

Edited by: Aishwarya Sharma on Oct 6, 2008 2:31 PM

[Former Member]

Hi Aishwarya,

What I understood is the HTTP Session is take care even if the currently serving node is crashed through session replication. Does this mean that the a session of WebDynpro application will continue to work or the changes are lost and the user needs to login again? Fundamentally the question is what WebDynpro uses behind the scenes for maintaining session?

Thanks and Regards,

Gaurav.