Enterprise Application Development : Azure Monitoring and Diagnostics

Logging config data in our application

Now that we have the collection of diagnostic data configured, we need to add code to our application to send diagnostic data to the listeners. We can do this simply by making calls to the methods in the System.Diagnostics.Trace class (documented at http://msdn.microsoft.com/en-us/library/36hhw2t6.aspx).

One of the more common methods we'll call is Trace.Writeline, as seen here:

Trace.Writeline("An error has occurred!","Error")

If our filter is set to the value Error or higher, our message would be logged. An alternative, easier syntax is:

Trace.TraceError("An error has occurred!")

Transferring and persisting diagnostic data

As diagnostic data are logged, the data are buffered in memory. In order for us to retain the data for analysis, we need to make sure that the data persists in a proper storage container. This is not set up by default, but it takes only a couple of lines of code to configure the transfer of data into the storage location. We can set this transfer to be either scheduled, or on demand.

To automatically transfer the diagnostic data on a schedule, we just need to add a single line to our role's OnStart method:

diagConfig.PerformanceCounters.ScheduledTransferPeriod = System.TimeSpan.FromMinutes(1.0)


					  

Public Overrides Function OnStart() As Boolean
OnStart methodDim diagConfig As DiagnosticMonitorConfiguration = DiagnosticMonitor.GetDefaultInitialConfiguration()
Dim procTimeConfig As PerformanceCounterConfiguration = New PerformanceCounterConfiguration()
procTimeConfig.CounterSpecifier = "\Processor(*)\% Processor Time"
procTimeConfig.SampleRate = System.TimeSpan.FromSeconds(1.0)
diagConfig.PerformanceCounters.DataSources.Add(procTimeConfig)
diagConfig.PerformanceCounters.ScheduledTransferPeriod = System.TimeSpan.FromMinutes(1.0)
DiagnosticMonitor.Start("DiagnosticsConnectionString")
Return MyBase.OnStart()
End Function


					  

We'll need to add similar code to the OnStart methods of the other roles in our application if we want to automatically transfer the diagnostic logs for those roles too.

An on-demand transfer is a little different an on-demand transfer can be initiated either from within the role, from another role in the same application, or even a completely different application. To reduce the amount of diagnostic data we need to sort through when debugging, we might want to log every level of diagnostic data but transfer the diagnostic data only when an error occurs.

Public Sub TransferDiagnosticData()
Dim diagManager As DeploymentDiagnosticManager = New DeploymentDiagnosticManager(<Azure storage account name>, <Azure deployment ID>)
dim roleInstDiagMgr as RoleInstanceDiagnosticManager = diagManager.GetRoleInstanceDiagnosticManager( <Role name>, <Role instance name>)
Dim dataBuffersToTransfer As DataBufferName = DataBufferName.Directories
Dim transferOptions As OnDemandTransferOptions = New OnDemandTransferOptions()
With transferOptions
.From = DateTime.MinValue
.To = DateTime.UtcNow
End With
Dim requestID As Guid = roleInstDiagMgr.BeginOnDemandTransfer(dataBuffersToTransfer, transferOptions)
End Sub


					  

It's important to note that diagnostic data is treated the same as any other data associated with our application, and we will be charged for the storage of the diagnostic output.

Accessing stored data

Once we've transferred the diagnostic data to storage, we can access it for analysis. Accessing log data is the same as accessing any other Table or Blob Storage. The most convenient way may be using the REST interface documented earlier in this book.

As Azure becomes more popular, third-party diagnostic tools will be developed. One such tool already available is the Cerebrata Azure Diagnostics Manager, found at http://www.cerebrata.com/Products/AzureDiagnosticsManager/Default.aspx. Hundreds of Azure-related applications have been added to Codeplex as well, but many of these projects have withered.