Monitoring your WCF services with AppFabric

Windows AppFabric (Previously known as Dublin) introduces a new built-in mechanism for monitoring the execution of the WCF services, all the events generated during the execution or the interaction with other services. While the message trace capabilities in WCF already provided some detail about the execution and the exchanged messages, it was a feature more suitable for troubleshooting and error diagnosis.   The performance counters did not help in this area either, as they provided live service usage statistics, which sometimes resulted very useful to determine possible bottlenecks.

When this monitoring mechanism is enabled for IIS Hosted services, the AppFabric extension will capture different events during the execution of the services. The level of detail or number of events that you want to capture is something that can be adjusted through configuration.

In order to configure monitoring for an existing WCF service, you need to add the following section to the web.config file,

      <default enabled="true" connectionStringName="DefaultApplicationServerExtensions" monitoringLevel="Troubleshooting" />

The connectionStringName attribute should contain a reference to an existing connection string in the ConnectionString section, and that’s the database used by AppFabric to store the monitoring events.

The monitoringLevel attribute specifies the number of events you want to capture in a service execution. The possible values for this setting are,

  • Off (monitoringLevel="Off”): No data is collected. It would be equivalent to have monitoring disabled.
  • Errors only (monitoringLevel="ErrorsOnly”):  Only errors and warnings events are collected. This is very useful when you don’t want to incur into performance issues for collecting application events but you still want to know about any error may happen during the execution.
  • Health Monitoring (monitoringLevel=HealthMonitoring): This is the default level and collects enough application events to show different metrics in the AppFabric dashboard.
  • End To End Monitoring (monitoringLevel="EndToEndMonitoring”). It collects all the events from the Health Monitoring level, plus additional events to reconstruct the message flow. For example, Service A called Service B. You will get also events representing info about the Service B call if monitoring is enabled on Service A.
  • Troubleshooting (monitoringLevel="Troubleshooting"). This is the most verbose of all, so it is appropriate for troubleshooting an unhealthy application.

All this monitoring infrastructure is layered on top of “Event Tracing for Windows (ETW)”, which provides a very efficient and optimized mechanism for capturing application events without affecting the application performance at all. In addition, this infrastructure is complemented with a windows service for collecting the events (A ETW listener basically), and providers for dumping all the information to different storages. This last part is totally extensible, and you can configure your own implementation by implementing the interface Microsoft.ApplicationServer.Monitoring.EventCollector.IBulkCopy in the Monitoring.ApplicationServer.Monitoring assembly. This interface looks quite simple to implement, and AppFabric ships with a default implementation for SQL Server.

public interface IBulkCopy
        int BatchSize { get; set; }
        DbConnection Connection { get; set; }
        string DestinationTableName { get; set; }

        void WriteToServer(DataTable dataTable);

The windows service for collecting the ETW events can be found under the folder, C:\Windows\System32\ApplicationServerExtensions\Microsoft.ApplicationServer.ServiceHost.exe, and it must be started in order to capture and dump the events in the configured IBulkCopy provider.

In addition, if you want to correlate all the service calls within a single execution (For example, Service A calling Service B, and B calling C) under a unique global identifier, so you can group all the events under that identifier, there is a new <endToEndTracing> element under the <system.ServiceModel/diagnostics> section that you can use.

  <diagnostics etwProviderId="7d98f890-ff8d-4311-be4f-e679103ba7cf">
    <endToEndTracing propagateActivity="true" messageFlowTracing="true" />

For example, the following image shows two events that are correlated under the same E2EActivityId, which represents a service “HelloWorld” calling an operation in another “EchoService” service.



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