Emmanuel's Screencasts

Windows Azure CloudDrive - Creating a Web Role that mounts the CloudDrive from Azure Storage and reads text files (Part 2 of 2, 22 minutes)

Here’s what is covered in the video:

• 00:00 - Introduction / Overview (see notes here).
• Mounting a VHD in the Azure fabric, reading text files and spitting them out
• 00:50 - New Visual Studio 2010 RC cloud project with one web role
• MyVHDWebRole - it's a Windows Azure web role but is like a console app - runs and spits out results.
• 01:40 - Settings in ServiceDefinition.csdef with LocalResource "on-disk" cache

<?xml version="1.0" encoding="utf-8"?>
<ServiceDefinition name="MyVHDWebRole" 
  xmlns="http://schemas.microsoft.com/ServiceHosting/2008/10/ServiceDefinition">
  <WebRole name="MyVHD_WebRole">
    <InputEndpoints>
      <InputEndpoint name="HttpIn" protocol="http" port="90" />
    </InputEndpoints>
    <ConfigurationSettings>
      <Setting name="DiagnosticsConnectionString" />
            <Setting name="AzureStorageAccount" />
            <Setting name="AzureStorageKey" />
            <Setting name="BlobStorageEndpoint" />
            <Setting name="QueueStorageEndpoint" />
            <Setting name="TableStorageEndpoint" />
            <Setting name="BlobContainePCLDrives" />
            <Setting name="VHDDriveName" />
        </ConfigurationSettings>
        <LocalResources>
            <LocalStorage name="MyCloudDriveCache"
                    cleanOnRoleRecycle="true"
                    sizeInMB="30" />
        </LocalResources>
    </WebRole>
</ServiceDefinition>

• 02:40 - Settings in ServiceConfiguration.cscfg with osVersion set to host OS 1.1 

<?xml version="1.0"?>
<ServiceConfiguration 
    serviceName="MyVHDWebRole" 
    osVersion="WA-GUEST-OS-1.1_201001-01"
    xmlns="http://schemas.microsoft.com/ServiceHosting/2008/10/ServiceConfiguration">
  <Role name="MyVHD_WebRole">
    <Instances count="1" />
    <ConfigurationSettings>
      <Setting name="DiagnosticsConnectionString" value="UseDevelopmentStorage=true" />
            <Setting name="AzureStorageAccount" value="devstoreaccount1" />
            <Setting name="AzureStorageKey" value="Eby8vdM02xNOcqFlqUwJPLlmEtlCDXJ1OUzFT50uSRZ6IFsuFq2UVErCz4I6tq/K1SZFPTOtr/KBHBeksoGMGw==" />
            <Setting name="BlobStorageEndpoint" value="http://127.0.0.1:10000/devstoreaccount1/" />
            <Setting name="QueueStorageEndpoint" value="http://127.0.0.1:10001/devstoreaccount1/" />
            <Setting name="TableStorageEndpoint" value="http://127.0.0.1:10002/devstoreaccount1/" />
            <Setting name="BlobContainePCLDrives" value="vhddrives" />
            <Setting name="VHDDriveName" value="myvhddrive.vhd" />
        </ConfigurationSettings>
  </Role>
</ServiceConfiguration>

Host 1.1 does not yet support .NET Framework 4.0 yet (in the cloud)
This sample uses the local development storage - not Azure Storage in the cloud

• 04:55 - Make sure your Page Blob snapshot and CloudDrive instance is public - so you can unmount and delete when the web role shuts down.
• Specially in developmnent, where for a example a 1 GB VHD would be copied to a 1 GB snapshot
• In the cloud, this is not true, a snapshot is very small - one page.
• 06:10 - Tip to read templates if running outside of local development fabric (in IIS for faster development)
• 06:30 - ASPX file - a button and a label - the label contains the results.
• If an exception occurs, it's easy to see it and follow up in the forums.
• 07:45 - We only enable the "Mount VHD" button if we are running in the fabric.
• 08:30 - Function BP() - just used to build up a string that is then displayed through the page's label.
• 09:20 - We dig into the cache code -

oLocalResource = RoleEnvironment.GetLocalResource("MyCloudDriveCache")
sCacheFolder = AddTrailingSlash(oLocalResource.RootPath) + "cache"
If Not (IO.Directory.Exists(sCacheFolder)) Then IO.Directory.CreateDirectory(sCacheFolder)

Make sure your cache folder does not have a trailing backslash "\" - the Azure SDK 1.1 has a bug that will throw an exception if it does.

• 10:30 - Telling the CloudDrive API to cache the VHD page blob -

CloudDrive.InitializeCache(sCacheFolder, oLocalResource.MaximumSizeInMegabytes)

• 11:00 - Do the Windows Azure dance to get a reference to the VHD stored in Azure Blob Storage

uriBlobStorageEndpoint = New Uri(sBlobStorageEndpoint)
uriQueueStorageEndpoint = New Uri(sQueueStorageEndpoint)
uriTableStorageEndpoint = New Uri(sTableStorageEndpoint)

oStorageCredentialsAccountAndKey = New StorageCredentialsAccountAndKey(sAzureStorageAccount, sAzureStorageKey)
oCloudStorageAccount = New CloudStorageAccount(oStorageCredentialsAccountAndKey, _ 
                           uriBlobStorageEndpoint, uriQueueStorageEndpoint, uriTableStorageEndpoint)

oCloudBlobClient = oCloudStorageAccount.CreateCloudBlobClient()
oCloudBlobContainer = oCloudBlobClient.GetContainerReference(sBlobContainePCLDrives)
oCloudBlobContainer.CreateIfNotExist()

• 11:35 - Creating an instance of the CloudDrive class -

' Existing Drive
oCloudPageBlob = oCloudBlobContainer.GetPageBlobReference(sVHDDriveName)
sVHDUri = oCloudPageBlob.Uri.ToString

• 12:00 - Creating a snapshot of the page blob and the read-only CloudDrive -

oCloudDrive = oCloudStorageAccount.CreateCloudDrive(sVHDUri)
uriVHDSnapshot = oCloudDrive.Snapshot
sVHDSnapshotUri = uriVHDSnapshot.ToString 

oCloudDriveReadOnly = New CloudDrive(uriVHDSnapshot, oCloudStorageAccount.Credentials)

• 12:45 - Mount the VHD drive in read-only mode -

sLocalPath = oCloudDriveReadOnly.Mount(oLocalResource.MaximumSizeInMegabytes, _ 
                                       DriveMountOptions.None)

Make sure you handle exceptions here!

• 13:45 - Use the regular System.IO classes to enumerate files in a folder in the VHD file -

If IO.Directory.Exists(sLocalPath) Then
  …
  sFiles = IO.Directory.GetFiles(sDataFolder, "*.TXT")
End If

Mentioned Visual Studio 2010 RC Code Snippets in VB.NET (for the C# developers, here’s a tutorial on code snippets).  Spent a bit of time to read the text content from each file and displayed it in the results.

• 16:50 - Running the web role in the Windows Azure local development fabric
• Showing the deployment in the service details
• Showing the default.aspx page in the browser.
• Clicked on 'Mount VHD' -
• Showed the snapshot directory in C:\Users\emmanuel_huna\AppData\Local\dftmp\wadd\devstoreaccount1\vhddrives\myvhddrive.vhd!2010-03-12T21_52_56.6300000Z
• Got exception on reading the contents since the filename contained the path already; fixed it and ran it again - it worked!
• 19:49 - When your web role shuts down: Un-mount your read-only CloudDrive and make sure you delete the Azure Page Blob snapshots.
• 21:40 - Conclusion.

Good times!