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Web Farm and Load Balancing

This help article explains the setup required for proper file uploads in a Web Farm when load balancing is used.

There are a few simple requirements that allow file uploads (including chunk file uploads) to arrive in the proper destination:

  • The TemporaryFolder and TargetFolder must be in a location shared among all servers. For example, TemporaryFolder="\\sharedNetworkDrive\myTempFolder".

    You can create a Virtual Directory under the WebApplication and point it to the shared network location. You can then use this virtual directory for the RadAsyncUpload TargetFolder and/or TemporaryFolder.

  • The Windows user account that the ApplicationPool uses must have permissions to read and write to these folders. Setting the UseApplicationPoolImpersonation property to true instructs the control to impersonate the application pool.

Depending on your host, you may find useful the built-in support RadCloudUpload offers for:


If files do not get written at all to the target folder, try giving Everyone permissions to the TargetFolder and TemporaryFolder. If this resolves the issue, then you need to locate the user that IIS operates under, and provide them with sufficient privileges. Set the UseApplicationPoolImpersonation property of the RadAsyncUpload to true.

Such a shared drive can be considered a single point of failure, which is something load balancing and web farms strive to avoid. If this is a concern in your use case, set DisableChunkUpload to true so that the files will be uploaded in one piece and use a custom upload handler to store them according to your application requirements.

Large files must be allowed by the server. For more details, see the Uploading large files article.

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