Question

I have an application that is deployed on Windows Azure, in the application there is a Report part, the reports works as shown below.

1. The application generates the report as a PDF file and save it in a certain folder in the application.
2. I have a PDF viewer in the application that takes the URL of the file and displays it.

As you know, in windows azure I will have several VMs that will handled through a Load balancer so I can not ensure that the request in step 2 will go to the same VM in step 1, and this will cause a problem for me.

Any help is very appreciated.

I know that I can use BLOB, but this is not the problem.
The problem is that after creating the file on a certain VM, I give the PDF viewer the url of the pdf viewer as “http://…./file.pdf”. This will generate a new request that I cannot control, and I cannot know which VM will server, so even I saved the file in the BLOB it will not solve my problem.

Answer 1

as in any farm environment, you have to consider saving files in a storage that is common for all machines in the farm. In Windows Azure, such common storage is Windows Azure Blob Storage.

You have to make some changes to your application, so that it saves the files to a Blob stroage. If these are public files, then you just mark the Blob Container as public and provide the full URL to the file in blob to the PDF viewer.

If your PDF files are private, you have to mark your container as private. Second step is to generate a Shared Access Signature URL for the PDF and provide that URL to the PDF viewer.

Furthermore, while developing you can explore your Azure storage using any of the (freely and not so freely) available tools for Windows Azure Storage. Here are some:

• Azure Storage Explorer
• Azure Cloud Storage Studio

There are a lot of samples how to upload file to Azure Storage. Just search it with your favorite search engine. Check out these resources:

• http://msdn.microsoft.com/en-us/library/windowsazure/ee772820.aspx
• http://blogs.msdn.com/b/windowsazurestorage/archive/2010/04/11/using-windows-azure-page-blobs-and-how-to-efficiently-upload-and-download-page-blobs.aspx
• http://wely-lau.net/2012/01/10/uploading-file-securely-to-windows-azure-blob-storage-with-shared-access-signature-via-rest-api/
• The Windows Azure Training Kit has great lab named "Exploring Windows Azure Storage"

Hope this helps!

UPDATE (following question update)

The problem is that after creating the file on a certain VM, I give
the PDF viewer the url of the pdf viewer as "http://…./file.pdf".
This will generate a new request that I cannot control, and I cannot
know which VM will server, so even I saved the file in the BLOB it
will not solve

Try changing a bit your logic, and follow my instructions. When your VM create the PDF, upload the file to a blob. Then give the full blob URL for your pdf file to the PDF viewer. Thus the request will not go to any VM, but just to the blob. And the full blob URL will be something like http://youraccount.blob.core.windows.net/public_files/file.pdf

Or I am missing something? What I understand, your process flow is as follows:

1. User makes a special request which would cause PDF file generation
2. File is generated on the server
3. full URL to the file is sent back to the client so that a client PDF viewer could render it

If this is the flow, that with suggested changes will look like the following:

1. User make a special request which would cause PDF file generation
2. File is generated on the server
3. File is uploaded to a BLOB storage
4. Full URL for the file in the BLOB is returned back to the client, so that it can be rendered on the client.

What is not clear? Or what is different in your process flow? I do exaclty the same for on-the-fly report generation and it works quite well. The only difference is that my app is Silverlight based and I force file download instead of inline-displaying.