Microsoft Diagnostics EventFlow
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README.md

Microsoft.Diagnostics.EventFlow

Introduction

The EventFlow library suite allows applications to define what diagnostics data to collect, and where they should be outputted to. Diagnostics data can be anything from performance counters to application traces. It runs in the same process as the application, so communication overhead is minimized. It also has an extensibility mechanism so additional inputs and outputs can be created and plugged into the framework. It comes with the following inputs and outputs:

Inputs

Outputs

The EventFlow suite supports .NET applications and .NET Core applications. It allows diagnostic data to be collected and transferred for applications running in these Azure environments:

  • Azure Web Apps
  • Service Fabric
  • Azure Cloud Service
  • Azure Virtual Machines

The core of the library, as well as inputs and outputs listed above are available as NuGet packages.

Getting Started

  1. To quickly get started, you can create a simple console application in VisualStudio and install the following Nuget packages:

    • Microsoft.Diagnostics.EventFlow.Inputs.Trace
    • Microsoft.Diagnostics.EventFlow.Outputs.ApplicationInsights
    • Microsoft.Diagnostics.EventFlow.Outputs.StdOutput
  2. Add a JSON file named "eventFlowConfig.json" to your project and set the Build Action property of the file to "Copy if Newer". Set the content of the file to the following:

{
    "inputs": [
    {
      "type": "Trace",
      "traceLevel": "Warning"
    }
  ],
  "outputs": [
    // Please update the instrumentationKey.
    {
      "type": "ApplicationInsights",
      "instrumentationKey": "00000000-0000-0000-0000-000000000000"
    }
  ],
  "schemaVersion": "2016-08-11"
}

Note: if you are using VisualStudio for Mac, you might need to edit the project file directly. Make the following snippet for eventFlowConfig.json file is included in the project definition:

<ItemGroup>
 <None Include="eventFlowConfig.json">
   <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
 </None>
</ItemGroup>
  1. If you wish to send diagnostics data to Application Insights, fill in the value for the instrumentationKey. If not, you can send traces to console output instead by replacing the Application Insights output with the standard output. The outputs property in the configuration should then look like this:
    "outputs": [
    {
      "type": "StdOutput"
    }
  ],
  1. Create an EventFlow pipeline in your application code using the code below. Make sure there is at least one output defined in the configuration file. Run your application and see your traces in console output or in Application Insights.
    using (var pipeline = DiagnosticPipelineFactory.CreatePipeline("eventFlowConfig.json"))
    {
        System.Diagnostics.Trace.TraceWarning("EventFlow is working!");
        Console.WriteLine("Trace sent to Application Insights. Press any key to exit...");
        Console.ReadKey(intercept: true);
    }

It usually takes a couple of minutes for the traces to show in Application Insights Azure portal.

Configuration Details

The EventFlow pipeline is built around three core concepts: inputs, outputs, and filters. The number of inputs, outputs, and filters depend on the need of diagnostics. The configuration also has a healthReporter and settings section for configuring settings fundamental to the pipeline operation. Finally, the extensions section allows declaration of custom developed plugins. These extension declarations act like references. On pipeline initialization, EventFlow will search extensions to instantiate custom inputs, outputs, or filters.

Inputs

These define what data will flow into the engine. At least one input is required. Each input type has its own set of parameters.

Trace

Nuget Package: Microsoft.Diagnostics.EventFlow.Inputs.Trace

This input listens to traces written with System.Diagnostics.Trace API. Here is an example showing all possible settings:

{
    "type": "Trace",
    "traceLevel":  "Warning"
}
Field Values/Types Required Description
type "Trace" Yes Specifies the input type. For this input, it must be "Trace".
traceLevel Critical, Error, Warning, Information, Verbose, All No Specifies the collection trace level. Traces with equal or higher severity than specified are collected. For example, if Warning is specified, then Critial, Error, and Warning traces are collected. Default is Error.

EventSource

Nuget Package: Microsoft.Diagnostics.EventFlow.Inputs.EventSource

This input listens to EventSource traces. EventSource classes can be created in the application by deriving from the System.Diagnostics.Tracing.EventSource class. Here is an example showing all possible settings:

{
    "type": "EventSource",
    "sources": [
        {
            "providerName": "MyEventSource",
            "level": "Informational",
            "keywords": "0x7F"
        }
    ]
}

Top object

Field Values/Types Required Description
type "EventSource" Yes Specifies the input type. For this input, it must be "EventSource".
sources JSON array Yes Specifies the EventSource objects to collect.

Source object (element of the sources array)

Field Values/Types Required Description
providerName EventSource name Yes(*) Specifies the name of the EventSource to track.
providerNamePrefix EventSource name prefix Yes(*) Specifies the name prefix of EventSource(s) to track. For example, if the value is "Microsoft-ServiceFabric", all EventSources that have names starting with Microsoft-ServiceFabric (Microsoft-ServiceFabric-Services, Microsoft-ServiceFabric-Actors and so on) will be tracked.
disabledProviderNamePrefix provider name Yes(*) Specifies the name prefix of the EventSource(s) that must be ignored. No events from these sources will be captured(***).
level Critial, Error, Warning, Informational, Verbose, LogAlways No(**) Specifies the collection trace level. Traces with equal or higher severity than specified are collected. For example, if Warning is specified, then Critial, Error, and Warning traces are collected. Default is LogAlways, which means "provider decides what events are raised", which usually results in all events being raised.
keywords An integer No(**) A bitmask that specifies what events to collect. Only events with keyword matching the bitmask are collected, except if it's 0, which means everything is collected. Default is 0.
eventCountersSamplingInterval An integer No Specifies the sampling interval in seconds for collecting data from EventCounters. Default is 0, which means no EventCounter data is collected.

Remarks

(*) Out of providerName, providerNamePrefix and disabledProviderNamePrefix, only one can be used for a single source. In other words, with a single source one can enable an EventSource by name, or enable a set of EventSources by prefix, or disable a set of EventSources by prefix.

(**) level and keywords can be used for enabling EventSources, but not for disabling them. Disabling events using level and keywords is not supported (but one can use level and/or keywords to selectively enable a subset of events from a given EventSource).

(***) There is an issue with .NET frameworks 4.6 and 4.7, and .NET Core framework 1.1 and 2.0 where dynamically created EventSource events are dispatched to all listeners, regardless whether listeners subscribe to events from these EventSources; for more information see https://github.com/dotnet/coreclr/issues/14434 disabledProviderNamePrefix property can be usesd to suppress these events.
Disabling EventSources is not recommended under normal circumstances, as it introduces a slight performance penalty. Instead, selectively enable necessary events through combination of EventSource names, event levels, and keywords.

PerformanceCounter

Nuget Package: Microsoft.Diagnostics.EventFlow.Inputs.PerformanceCounter

This input enables gathering data from Windows performance counters. Only process-specific counters are supported, that is, the counter must have an instance that is associated with the current process. For machine-wide counters use an external agent such as Azure Diagnostics Agent or create a custom input.

Finding the counter instance that corresponds to the current process

In general there is no canonical way to find a performance counter instance that corresponds to current process. Two methods are commonly used in practice:

  • A special performance counter that provides instance name to process ID mapping. This solution involves a set of counters that use the same instance name for a given process. Among them there is a special counter with a value that is the process ID of the corresponding process. Searching for the instance of the special counter with a value equal to the current process ID allows to discover what the instance name is used for the current process. Examples of this approach include the Windows Process category (special counter "ID Process") and all .NET counters (special counter "Process ID" in the ".NET CLR Memory" category).

  • Process ID can be encoded directly into the instance name. .NET performance counters can use this approach when ProcessNameFormat flag is set in the in the registry.

EventFlow PerformanceCounter input supports the first method of deterimining counter instance name for current process via configuration settings. It also supports the second method, but only for .NET performance counters.

Configuration example

{
    "type": "PerformanceCounter",
    "sampleIntervalMsec": "5000",
    "counters": [
        {
            "counterCategory": "Process",
            "counterName": "Private Bytes"
        }, 
        {
            "counterCategory": ".NET CLR Exceptions",
            "counterName": "# of Exceps Thrown / sec"
        }
    ]
}

Top-level configuration settings

Field Values/Types Required Description
type "PerformanceCounter" Yes Specifies the input type. For this input, it must be "PerformanceCounter".
sampleIntervalMsec integer No Specifies the sampling rate for the whole input (in milliseconds). This is the rate at which the collection loop for the whole input executes. Default is 10 seconds.
counters JSON array of Counter objects Yes Specifies performance counters to collect data from.

Counter class

Field Values/Types Required Description
counterCategory string Yes Category of the performance counter to monitor
counterName string Yes Name of the counter to monitor.
collectionIntervalMsec integer No Sampling interval for the counter. Values for the counter are read not more often than at this rate. Default is 30 seconds.
processIdCounterCategory and processIdCounterName string No The category and name of the performance counter that provides process ID to counter instance name mapping. It is not necessary to specify these for the "Process" counter category and for .NET performance counters.
useDotNetInstanceNameConvention boolean No Indicates that the counter instance names include process ID as described in ProcessNameFormat documentation.

Important usage note

Some performance counters require the user to be a member of the Performance Monitor Users system group. This can manifest itself by health reporter reporting "category does not exist" errors from PerformanceCounter output, despite the fact that the category and counter are properly configured and clearly visible in Windows Performance Monitor. If you need to consume such counters, make sure the account your process runs under belongs to Performance Monitor Users group.

Serilog

Nuget package: Microsoft.Diagnostics.EventFlow.Inputs.Serilog

This input enables capturing diagnostic data created through Serilog library.

Configuration example The Serilog input has no configuration, other than the "type" property that specifies the type of the input (must be "Serilog"):

{
  "type": "Serilog"
}

Example: instantiating a Serilog logger that uses EventFlow Serilog input

using System;
using System.Linq;
using Microsoft.Diagnostics.EventFlow;
using Serilog;

namespace SerilogEventFlow
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var pipeline = DiagnosticPipelineFactory.CreatePipeline(".\\eventFlowConfig.json"))
            {
                Log.Logger = new LoggerConfiguration()
                    .WriteTo.EventFlow(pipeline)
                    .CreateLogger();

                Log.Information("Hello from {friend} for {family}!", "SerilogInput", "EventFlow");
                
                Log.CloseAndFlush();
                Console.ReadKey();
            }
        }
    }
}

Microsoft.Extensions.Logging

Nuget package: Microsoft.Diagnostics.EventFlow.Inputs.MicrosoftLogging

This input enables capturing diagnostic data created through Microsoft.Extensions.Logging library and ILogger interface.

Configuration example The ILogger input has no configuration, other than the "type" property that specifies the type of the input (must be "Microsoft.Extensions.Logging"):

{
  "type": "Microsoft.Extensions.Logging"
}

Example: instantiating a ILogger that uses EventFlow ILogger input

using Microsoft.Diagnostics.EventFlow;
using Microsoft.Extensions.Logging;

namespace LoggerEventFlow
{
    class Program
    {
        static void Main(string[] args)
        {
            using (var pipeline = DiagnosticPipelineFactory.CreatePipeline(".\\eventFlowConfig.json"))
            {
                var factory = new LoggerFactory()
                    .AddEventFlow(pipeline);

                var logger = new Logger<Program>(factory);
                using (logger.BeginScope(myState))
                {
                    logger.LogInformation("Hello from {friend} for {family}!", "LoggerInput", "EventFlow");
                }
            }
        }
    }
}

Example: using EventFlow ILogger input with ASP.NET Core The following example shows how to enable EventFlow ILogger inside a Service Fabric stateless service that uses ASP.NET Core.

  1. Modify the service class so that its constructor takes a DiagnosticPipeline instance as a parameter:
        private static void Main()
        {
            try
            {
                using (ManualResetEvent terminationEvent = new ManualResetEvent(initialState: false))
                using (var pipeline = ServiceFabricDiagnosticPipelineFactory.CreatePipeline("CoreBasedFabricPlusEventFlow-Diagnostics"))
                {
                    Console.CancelKeyPress += (sender, eventArgs) => Shutdown(diagnosticsPipeline, terminationEvent);

                    AppDomain.CurrentDomain.UnhandledException += (sender, unhandledExceptionArgs) =>
                    {
                        ServiceEventSource.Current.UnhandledException(unhandledExceptionArgs.ExceptionObject?.ToString() ?? "(no exception information)");
                        Shutdown(diagnosticsPipeline, terminationEvent);
                    };

                    ServiceRuntime.RegisterServiceAsync("Web1Type",
                        context => new Web1(context, pipeline)).GetAwaiter().GetResult();

                    ServiceEventSource.Current.ServiceTypeRegistered(Process.GetCurrentProcess().Id, typeof(Web1).Name);

                    terminationEvent.WaitOne();
                }
            }
            catch (Exception e)
            {
                ServiceEventSource.Current.ServiceHostInitializationFailed(e.ToString());
                throw;
            }
        }

        private static void Shutdown(IDisposable disposable, ManualResetEvent terminationEvent)
        {
            try
            {
                disposable.Dispose();
            }
            finally
            {
                terminationEvent.Set();
            }
        }
  1. In the CreateServiceInstanceListeners() method add the pipeline as a singleton service to ASP.NET dependency injection container
        protected override IEnumerable<ServiceInstanceListener> CreateServiceInstanceListeners()
        {
            return new ServiceInstanceListener[]
            {
                new ServiceInstanceListener(serviceContext =>
                    new WebListenerCommunicationListener(serviceContext, "ServiceEndpoint", (url, listener) =>
                    {
                        ServiceEventSource.Current.ServiceMessage(serviceContext, $"Starting WebListener on {url}");

                        return new WebHostBuilder().UseWebListener()
                                    .ConfigureServices(
                                        services => services
                                            .AddSingleton<StatelessServiceContext>(serviceContext)
                                            .AddSingleton<DiagnosticPipeline>(this.diagnosticPipeline))
                                    .UseContentRoot(Directory.GetCurrentDirectory())
                                    .UseStartup<Startup>()
                                    .UseApplicationInsights()
                                    .UseServiceFabricIntegration(listener, ServiceFabricIntegrationOptions.None)
                                    .UseUrls(url)
                                    .Build();
                    }))
            };
        }
  1. In the Startup class configure the loggerFactory by calling AddEventFlow on it:
        public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
        {
            loggerFactory.AddConsole(Configuration.GetSection("Logging"));
            loggerFactory.AddDebug();
            var diagnosticPipeline = app.ApplicationServices.GetRequiredService<DiagnosticPipeline>();
            loggerFactory.AddEventFlow(diagnosticPipeline);

            app.UseMvc();
        }
  1. Now you can assume the logger factory will be constructor-injected into your controllers:
    [Route("api/[controller]")]
    public class ValuesController : Controller
    {
        private readonly ILogger<ValuesController> logger;

        public ValuesController(ILogger<ValuesController> logger)
        {
            this.logger = logger;
        }

        // GET api/values
        [HttpGet]
        public IEnumerable<string> Get()
        {
            this.logger.LogInformation("Hey, someone just called us!");
            return new string[] { "value1", "value2" };
        }

      // (rest of controller code is irrelevant)

ETW (Event Tracing for Windows)

Nuget package: Microsoft.Diagnostics.EventFlow.Inputs.Etw

This input captures data from Microsoft Event Tracing for Windows (ETW) providers. Both manifest-based providers as well as providers based on managed EventSource infrastructure are supported. The data is captured machine-wide and requires that the identity the process uses belongs to Performance Log Users built-in administrative group.

Note

To capture data from EventSources running in the same process as EventFlow, the EventSource input is a better choice, with better performance and no additional security requirements.

Configuration example

{
    "type": "ETW",
    "sessionNamePrefix": "MyCompany-MyApplication",
    "cleanupOldSessions": true,
    "reuseExistingSession": true,
    "providers": [
        {
            "providerName": "Microsoft-ServiceFabric",
            "level": "Warning",
            "keywords": "0x7F"
        }
    ]
}

Top Object

Field Values/Types Required Description
type "ETW" Yes Specifies the input type. For this input, it must be "ETW".
sessionNamePrefix string No The ETW trace session will be created with this name prefix, which helps in differentiating ETW input instances owned by multiple applications. If not set, a default prefix will be used.
cleanupOldSessions boolean No If set, existing ETW trace sessions matching the sessionNamePrefix will be closed. This helps to collect leftover session instances, as there is a limit on their number.
reuseExistingSession boolean No If turned on, then an existing trace session matching the sessionNamePrefix will be re-used. If cleanupOldSessions is also turned on, then it will leave one session open for re-use.
providers JSON array Yes Specifies ETW providers to collect data from.

Providers object

Field Values/Types Required Description
providerName provider name Yes(*) Specifies the name of the ETW provider to track.
providerGuid provider GUID Yes(*) Specifies the GUID of the ETW provider to track.
level Critial, Error, Warning, Informational, Verbose, LogAlways No Specifies the collection trace level. Traces with equal or higher severity than specified are collected. For example, if Warning is specified, then Critial, Error, and Warning traces are collected. Default is LogAlways, which means "provider decides what events are raised", which usually results in all events being raised.
keywords An integer No A bitmask that specifies what events to collect. Only events with keyword matching the bitmask are collected, except if it's 0, which means everything is collected. Default is 0.

(*) Either providerName, or providerGuid must be specified. When both are specified, provider GUID takes precedence.

Application Insights input

Nuget package: Microsoft.Diagnostics.EventFlow.Inputs.ApplicationInsights

Application Insights input is designed for the following scenario:

  1. You have an application that uses Application Insights for monitoring and diagnostics.
  2. You want to send a portion of your Application Insights telemetry to some destination other than Application Insights (e.g. Azure EventHub or Elasticsearch; the assumption is there is an EventFlow output for where the data needs to go).

For example, you might want to leverage Application Insights sampling capabilities to reduce the amount of data analyzed by Application Insights without losing analysis fidelity, while sending full raw logs to Elasticsearch to do detailed log search during problem troubleshooting.

Usage

  1. Add the EventFlowTelemetryProcessor to your Application Insights configuration file (it goes into TelemetryProcessors element):

    <ApplicationInsights xmlns="http://schemas.microsoft.com/ApplicationInsights/2013/Settings" >
      <!-- ... -->
      <TelemetryProcessors>
         <!-- ... -->
         <Add Type="Microsoft.Diagnostics.EventFlow.ApplicationInsights.EventFlowTelemetryProcessor, Microsoft.Diagnostics.EventFlow.Inputs.ApplicationInsights" />
         <!-- ... -->
      </TelemetryProcessors>
      <!-- ... -->
    </ApplicationInsights>

    Note that the order of telemetry processors does matter. In particular, if the EventFlowTelemetryProcessor is placed before the Application Insights sampling processor, EventFlow will capture all telemetry, but if the EventFlowTelemetryProcessor is placed after the sampling processor, it will only "see" telemetry that was sampled in. For more information on configuring Application Insights see Application Insights configuration documentation.

  2. In the EventFlow configuration make sure to include the Application Insights input. It does not take any parameters:

    { "type": "ApplicationInsights" }
  3. In your application code, after the EventFlow pipeline is created, find the EventFlowTelemetryProcessor and set its Pipeline property to the instance of the EventFlow pipeline:

    using (var pipeline = DiagnosticPipelineFactory.CreatePipeline("eventFlowConfig.json"))
    {
        // ...
        EventFlowTelemetryProcessor efTelemetryProcessor = TelemetryConfiguration.Active.TelemetryProcessors.OfType<EventFlowTelemetryProcessor>().First();
        efTelemetryProcessor.Pipeline = pipeline;
        // ...
    }

This is it-after the EventFlowTelemetryProcessor.Pipeline property is set, the EventFlowTelemetryProcessor will start sending AI telemetry into the EventFlow pipeline.

Application Insights input supports all standard Application Insights telemetry types: trace, request, event, dependency, metric, exception, page view and availability.

Outputs

Outputs define where data will be published from the engine. It's an error if there are no outputs defined. Each output type has its own set of parameters.

StdOutput

Nuget Package: Microsoft.Diagnostics.EventFlow.Outputs.StdOutput

This output writes data to the console window. Here is an example showing all possible settings:

{
    "type": "StdOutput"
}
Field Values/Types Required Description
type "StdOutput" Yes Specifies the output type. For this output, it must be "StdOutput".

Http

Nuget Package: Microsoft.Diagnostics.EventFlow.Outputs.HttpOutput

This output writes data to a webserver using diffent encoding methods (Json or JsonLines, eg. for logstash). Here is an example showing all possible settings:

{
    "type": "Http",
    "serviceUri": "https://example.com/",
    "format": "Json",
    "httpContentType": "application/x-custom-type",
    "basicAuthenticationUserName": "httpUser1",
    "basicAuthenticationUserPassword": "<MyPassword>"
}
Field Values/Types Required Description
type "Http" Yes Specifies the output type. For this output, it must be "Http".
serviceUri string Yes Target service URL endpoint (can be HTTP and HTTPS)
format "Json", "JsonLines" No Defines the message format (and the default HTTP Content-Type header). "Json" a json object with multiple array items and "JsonLines" one line per json object (multiple objects)
basicAuthenticationUserName string No Specifies the user name used to authenticate with webserver.
basicAuthenticationUserPassword string No Specifies the password used to authenticate with webserver. This field should be used only if basicAuthenticationUserName is specified.
httpContentType string No Defines the HTTP Content-Type header

Event Hub

Nuget Package: Microsoft.Diagnostics.EventFlow.Outputs.EventHub

This output writes data to the Azure Event Hub. Here is an example showing all possible settings:

{
    "type": "EventHub",
    "eventHubName": "myEventHub",
    "connectionString": "Endpoint=sb://<myEventHubNamespace>.servicebus.windows.net/;SharedAccessKeyName=RootManageSharedAccessKey;SharedAccessKey=<MySharedAccessKey>"
}
Field Values/Types Required Description
type "EventHub" Yes Specifies the output type. For this output, it must be "EventHub".
eventHubName event hub name No Specifies the name of the event hub.
connectionString connection string Yes Specifies the connection string for the event hub. The corresponding shared access policy must have send permission. If the event hub name does not appear in the connection string, then it must be specified in the eventHubName field.
partitionKeyProperty string No The name of the event property that will be used as the PartitionKey for the Event Hub events.

Application Insights

Nuget Package: Microsoft.Diagnostics.EventFlow.Outputs.ApplicationInsights

This output writes data to the Azure Application Insights service. Here is an example showing all possible settings:

{
    "type": "ApplicationInsights",
    "instrumentationKey": "00000000-0000-0000-0000-000000000000",
    "configurationFilePath": "path-to-ApplicationInsights.config"
}
Field Values/Types Required Description
type "ApplicationInsights" Yes Specifies the output type. For this output, it must be "ApplicationInsights".
instrumentationKey GUID No Specifies the instrumentation key for the targeted Application Insights resource. The key is in the form of a GUID. The key can be found on the Application Insights blade in Azure Portal. The value in this field overrides any value in the Application Insights configuration file (see the configurationFilePath parameter below). If configurationFilePath is not set, instrumentation key must be specified.
configurationFilePath string No Specifies the path to Application Insights configuration file. This parameter is optional-if no value is specified, default configuration for the Application Insights output will be used. For more information see Application Insights documentation

In Service Fabric environment the Application Insights configuration file can should be part of the default service configuration package (the 'Config' package). To resolve the path of the configuration file within the service configuration package set the value of configurationFilePath to servicefabricfile:/ApplicationInsights.config. For more information on this syntax see Service Fabric support

Standard metadata support

Application Insights output supports all standard metadata (request, metric, dependency and exception). Each of these metadata types corresponds to a native Application Insights telemetry type, enabling rich support for visualization and alerting that Application Insights provides. The Application Insights output also supports event metadata (corresponding to AI event telemetry type). This metadata is meant to represent significant application events, like a new user registered with the system or a new version of the code being deployed. Event metadata supports following properties:

Field Values/Types Required Description
metadata "ai_event" Yes Indicates Application Insights event metadata; must be "ai_event".
eventNameProperty string (see Remarks) The name of the event property that will be used as the name of the AI event telemetry.
eventName string (see Remarks) The name of the event (if the name is supposed to be taken verbatim from metadata).

Remarks:

  1. Either eventNameProperty or eventName must be given.

All other events will be reported as Application Insights traces (telemetry of type Trace).

Elasticsearch

Nuget Package: Microsoft.Diagnostics.EventFlow.Outputs.ElasticSearch

Note: Nuget package version 1.x supports Elasticsearch version 2.x. Nuget package version 2.x supports Elasticsearch version 6.x

This output writes data to the Elasticsearch. Here is an example showing all possible settings:

{
    "type": "ElasticSearch",
    "indexNamePrefix": "app1",
    "serviceUri": "https://myElasticSearchCluster:9200;https://myElasticSearchCluster:9201;https://myElasticSearchCluster:9202",
    "connectionPoolType": "Sniffing",
    "basicAuthenticationUserName": "esUser1",
    "basicAuthenticationUserPassword": "<MyPassword>",
    "eventDocumentTypeName": "diagData",
    "numberOfShards": 1,
    "numberOfReplicas": 1,
    "refreshInterval": "15s"
}
Field Values/Types Required Description
type "ElasticSearch" Yes Specifies the output type. For this output, it must be "ElasticSearch".
indexNamePrefix string No Specifies the prefix to be used when creating the Elasticsearch index. This prefix, together with the date of when the data was generated, will be used to form the name of the Elasticsearch index. If not specified, a prefix will not be used.
serviceUri URL:port Yes Specifies where the Elasticsearch cluster is. This is needed for EventFlow to locate the cluster and send the data. Single URL or semicolon-separated URLs for connection pooling are accepted
connectionPoolType "Static", "Sniffing", or "Sticky" No Specifies the Connection Pool that takes care of registering what nodes there are in the cluster.
basicAuthenticationUserName string No Specifies the user name used to authenticate with Elasticsearch. To protect the cluster, authentication is often setup on the cluster.
basicAuthenticationUserPassword string No Specifies the password used to authenticate with Elasticsearch. This field should be used only if basicAuthenticationUserName is specified.
eventDocumentTypeName string Yes Specifies the document type to be applied when data is written. Elasticsearch allows documents to be typed, so they can be distinguished from other types. This type name is user-defined.
numberOfShards int No Specifies how many shards to create the index with. If not specified, it defaults to 1.
numberOfReplicas int No Specifies how many replicas the index is created with. If not specified, it defaults to 5.
refreshInterval string No Specifies what refresh interval the index is created with. If not specified, it defaults to 15s.

Standard metadata support

Elasticsearch output supports all standard metadata types. Events decorated with metadata will get additional properties when sent to Elasticsearch.

Fields injected by metric metadata are:

Field Description
MetricName The name of the metric, read directly from the metadata.
Value The value of the metric, read from the event property specified by metricValueProperty.

Fields injected byt the request metadata are:

Field Description
RequestName The name of the request, read the event property specified by requestNameProperty.
Duration Request duration, read from the event property specified by durationProperty (if available).
IsSuccess Success indicator, read from the event property specified by isSuccessProperty (if available).
ResponseCode Response code for the request, read from the event property specified by responseCodeProperty (if available).

OMS (Operations Management Suite)

Nuget package: Microsoft.Diagnostics.EventFlow.Outputs.Oms

The OMS output writes data to Operations Management Suite Log Analytics workspaces. You will need to create a Log Analytics workspace in Azure and know its ID and key before using OMS output. Here is a sample configuration fragment enabling the output:

{
  "type": "OmsOutput",
  "workspaceId": "<workspace-GUID>",
  "workspaceKey": "<base-64-encoded workspace key>",
  "serviceDomain" : "<optional domain for OMS>"
}

Supported configuration settings are:

Field Values/Types Required Description
type "OmsOutput" Yes Specifies the output type. For this output, it must be "OmsOutput".
workspaceId string (GUID) Yes Specifies the workspace identifier.
workspaceKey string (base-64) Yes Specifies the workspace authentication key.
logTypeName string No Specifies the log entry type created by the output. Default value for this setting is "Event", which results in "Event_CL" entries being created in OMS (the "_CL" suffix is appended automatically by OMS
ingestion service).
serviceDomain string No Specifies the domain for your OMS workspace. Default value is "ods.opinsights.azure.com", for Azure Commercial.

Filters

As data comes through the EventFlow pipeline, the application can add extra processing or tagging to them. These optional operations are accomplished with filters. Filters can transform, drop, or tag data with extra metadata, with rules based on custom expressions. With metadata tags, filters and outputs operating further down the pipeline can apply different processing for different data. For example, an output component can choose to send only data with a certain tag. Each filter type has its own set of parameters.

Filters can appear in two places in the EventFlow configuration: on the same level as inputs and outputs (global filters) and as part of output declaration (output-specific filters). Global filters are applied to all data coming from the inputs. Output-specific filters are applied to just one output, just before the data reaches the output. Here is an example with two global filters and one output-specific filter:

{
    "inputs": [...],

    "filters": [
        // The following are global filters
        {
            "type": "drop",
            "include": "..."
        },
        {
            "type": "drop",
            "include": "..."
        }
    ],

    "outputs": [
        {
            "type": "ApplicationInsights",
            "instrumentationKey": "00000000-0000-0000-0000-000000000000",
            "filters": [
                {
                    "type": "metadata",
                    "metadata": "metric",
                    // ... 
                }
            ]
        }
    ]
}

EventFlow comes with two standard filter types: drop and metadata.

drop

Nuget Package: Microsoft.Diagnostics.EventFlow.Core

This filter discards all data that satisfies the include expression. Here is an example showing all possible settings:

{
    "type": "drop",
    "include": "Level == Verbose || Level == Informational"
}
Field Values/Types Required Description
type "drop" Yes Specifies the filter type. For this filter, it must be "drop".
include logical expression Yes Specifies the logical expression that determines if the action should apply to the event data or not. For information about the logical expression, please see section Logical Expressions.

metadata

Nuget Package: Microsoft.Diagnostics.EventFlow.Core

This filter adds additional metadata to all event data that satisfies the include expression. The filter recognizes a few standard properties (type, metadata and include); the rest are custom properties, specific for the given metadata type:

{
    "type": "metadata",
    "metadata": "metric",
    "include": "ProviderName == MyEventProvider && EventId == 3",
    "customTag1": "tag1",
    "customTag2": "tag2"
}
Field Values/Types Required Description
type "metadata" Yes Specifies the filter type. For this filter, it must be "metadata".
metadata string Yes Specifies the metadata type. This field is used only if type is "metadata", so it shouldn't appear in other filter types. The metadata type is user-defined and is persisted along with metadata tag added to the event data.
include logical expression Yes Specifies the logical expression that determines if the metadata is applied to the event data. For information about the logical expression, please see section Logical Expressions.
[others] string No Specifies custom properties that should be added along with this metadata object. When the event data is processed by other filters or outputs, these properties can be accessed. The names of these properties are custom-defined and the possible set is open-ended. For a particular filter, zero or more custom properties can be defined. In the example above, customTag1 and customTag2 are such properties.

Here are a few examples of using the metadata filter:

  1. Submit a metric with a value of 1 (a counter) whenever there is a Service Fabric stateful service run failure

    {
    "type": "metadata",
    "metadata": "metric",
    "include": "ProviderName==Microsoft-ServiceFabric-Services 
                && EventName==StatefulRunAsyncFailure",
    "metricName": "StatefulRunAsyncFailure",
    "metricValue": "1.0"
    }
  2. Turn processor time performance counter into a metric

    {
      "type": "metadata",
      "metadata": "metric",
      "include": "ProviderName==EventFlow-PerformanceCounterInput && CounterCategory==Process 
                  && CounterName==\"% Processor Time\"",
      "metricName": "MyServiceProcessorTimePercent",
      "metricValueProperty": "Value"
    }
  3. Turn a custom EventSource event into a request. The event has 3 interesting properties: requestTypeName indicates what kind of request it was; durationMsec has the total request processing duration and ‘isSuccess’ indicates whether the processing succeeded or failed

    {
      "type": "metadata",
      "metadata": "request",
      "include": "ProviderName==MyCompany-MyApplication-FrontEndService 
                  && EventName==ServiceRequestStop",
      "requestNameProperty": "requestTypeName",
      "durationProperty": "durationMsec",
      "isSuccessProperty": "isSuccess"
    }

Standard metadata types

EventFlow core library defines several standard metadata types. They have pre-defined set of fields and are recognized by Application Insights and Elasticsearch outputs (see documentation for each output, respectively, to learn how they handle standard metadata).

Metric metadata type

Metrics are named time series of floating-point values. Metric metadata defines how metrics are derived from ordinary events. Following fields are supported:

Field Values/Types Required Description
metadata "metric" Yes Indicates metric metadata definition; must be "metric".
metricName string (see Remarks) The name of the metric.
metricNameProperty string (see Remarks) The name of the event property that holds metric name.
metricValue double (see Remarks) The value of the metric. This is useful for "counter" type of metric when each occurrence of a particular event should result in an increment of the counter.
metricValueProperty string (see Remarks) The name of the event property that holds the metric value.

Remarks:

  1. Either metricName or metricNameProperty must be specified.
  2. Either metricValue or metricValueProperty must be specified.

Request metadata type

Requests are special events that represent invocations of a network service by its clients. Request metadata defines how requests are derived from ordinary events. Following fields are supported:

Field Values/Types Required Description
metadata "request" Yes Indicates request metadata definition; must be "request".
requestNameProperty string Yes The name of the event property that contanis the name of the request (to distinguish between different kinds of requests).
isSuccessProperty string No The name of the event property that specifies whether the request ended successfully. It is expected that the event property is, or can be converted to a boolean.
durationProperty string No The name of the event property that specifies the request duration (execution time).
durationUnit "TimeSpan", "milliseconds", "seconds", "minutes" or "hours" No Specifies the type of data used by request duration property. If not set, it is assumed that request duration is expressed as a double value, representing milliseconds.
responseCodeProperty string No The name of the event property that specifies response code associated with the request. A response code describes in more detail the outcome of the request. It is expected that the event property is, or can be converted to a string.

Dependency metadata type

Dependency event represents the act of calling a service that your service depends on. It has the following properties:

Field Values/Types Required Description
metadata "dependency" Yes Indicates dependency metadata definition; must be "dependency".
isSuccessProperty string No The name of the event property that specifies whether the request ended successfully. It is expected that the event property is, or can be converted to a boolean.
durationProperty string No The name of the event property that specifies the request duration (execution time).
durationUnit "TimeSpan", "milliseconds", "seconds", "minutes" or "hours" No Specifies the type of data used by request duration property. If not set, it is assumed that request duration is expressed as a double value, representing milliseconds.
responseCodeProperty string No The name of the event property that specifies response code associated with the request. A response code describes in more detail the outcome of the request. It is expected that the event property is, or can be converted to a string.
targetProperty string Yes The name of the event property that specifies the target of the call, i.e. the identifier of the service that your service depends on.
dependencyType string No An optional, user-defined designation of the dependency type. For example, it could be "SQL", "cache", "customer_data_service" or similar.

Exception metadata type

Exception event corresponds to an occurrence of an unexpected exception. Usually a small amount of exceptions is continuously being thrown, caught and handled by a .NET process, this is normal and should not raise a concern. On the other hand, if an exception is unhandled, or unexpected, it needs to be logged and examined. This metadata is meant to cover the second case. It has the following properties:

Field Values/Types Required Description
metadata "exception" Yes Indicates exception metadata definition; must be "exception".
exceptionProperty System.Exception Yes The name of the event property that carries the (unexpected) exception object. Note that (for maximum information fidelity) the expected type of the event property is System.Exception. In other words, the actual exception is expected to be part of event data, and not just a stringified version of it.

Also see Application Insight Exception metadata type with EvenSource input issue

Health Reporter

Every software component can generate errors or warnings the developer should be aware of. The EventFlow library is no exception. An EventFlow health reporter reports errors and warnings generated by any components in the EventFlow pipeline. In what format the report is presented depends on the implementation of the health reporter. The EventFlow library suite includes two health reporters: CsvHealthReporter and ServiceFabricHealthReporter.

The CsvHealthReporter is the default health reporter for EventFlow library and is used if the health reporter configuration section is omitted. Its configuration parameters are described below.

ServiceFabricHealthReporter is described in the Service Fabric support paragraph. It is designed to be used in the context of Service Fabric applications and does not need any configuration.

CsvHealthReporter

Nuget Package: Microsoft.Diagnostics.EventFlow.Core

This health reporter writes all errors, warnings, and informational traces generated from the pipeline into a CSV file. Here is an example showing all possible settings:

"healthReporter": {
    "type": "CsvHealthReporter",
    "logFileFolder": ".",
    "logFilePrefix": "HealthReport",
    "minReportLevel": "Warning",
    "throttlingPeriodMsec": "1000",
    "singleLogFileMaximumSizeInMBytes": "8192",
    "logRetentionInDays": "30",
    "ensureOutputCanBeSaved": "false"
}
Field Values/Types Required Description
type "CsvHealthReporter" Yes Specifies the health reporter type. For this reporter, it must be "CsvHealthReporter".
logFileFolder file path No Specifies a path for the CSV log file to be written. It can be an absolute path, or a relative path. If it's a relative path, then it's computed relative to the directory where the EventFlow core library is in. However, if it's an ASP.NET application, it's relative to the app_data folder.
logFilePrefix file path No Specifies a prefix used for the CSV log file. CsvHealthReporter creates the log file name by combining this prefix with the date of when the file is generated. If the prefix is omitted, then a default prefix of "HealthReport" is used.
minReportLevel Error, Warning, Message No Specifies the collection report level. Report traces with equal or higher severity than specified are collected. For example, if Warning is specified, then Error, and Warning traces are collected. Default is Error.
throttlingPeriodMsec number of milliseconds No Specifies the throttling time period. This setting protects the health reporter from being overwhelmed, which can happen if a message is repeatedly generated due to an error in the pipeline. Default is 0, for no throttling.
singleLogFileMaximumSizeInMBytes File size in MB/number No Specifies the size of the log file in MB before rotating happens. The default value is 8192 MB (8 GB). Once the size of log file exceeds the value, it will be renamed from fileName.csv to fileName_last.csv. Then logs will be written to a new fileName.csv. This setting prevents a single log file become too big.
logRetentionInDays number of days for the logs files retain No Specifies how long log files will be retained. The default value is 30 days. Any log files created earlier than the specified number of days ago will be removed automatically. This prevents continuous generation of logs that might lead to storage exhaustion.
ensureOutputCanBeSaved boolean No Specifies whether the health reporter is going to ensure the permission to write to the log folder. The default value is false. When set to true, it will prevent the pipeline creation when it can't write the log. Otherwise, it will ignore the error.

CsvHealthReporter will try to open the log file for writing during initialization. If it can't, by default, a debug message will be output to the debugger viewer like Visual Studio Output window, etc. This can happen especially if a value for the log file path is not provided (default is used, which is application executables folder) and the application executables are residing on a read-only file system. Docker tools for Visual Studio use this configuration during debugging, so for containerized services the recommended practice is to specify the log file path explicitly.

Pipeline Settings

The EventFlow configuration has settings allowing the application to adjust certain behaviors of the pipeline. These range from how many events the pipeline buffer, to the timeout the pipeline should use when waiting for an operation. If this section is omitted, the pipeline will use default settings. Here is an example of all the possible settings:

"settings": {
    "pipelineBufferSize": "1000",
    "maxEventBatchSize": "100",
    "maxBatchDelayMsec": "500",
    "maxConcurrency": "8",
    "pipelineCompletionTimeoutMsec": "30000"
}
Field Values/Types Required Description
pipelineBufferSize number No Specifies how many events the pipeline can buffer if the events cannot flow through the pipeline fast enough. This buffer protects loss of data in cases where there is a sudden burst of data.
maxEventBatchSize number No Specifies the maximum number of events to be batched before the batch gets pushed through the pipeline to filters and outputs. The batch is pushed down when it reaches the maxEventBatchSize, or its oldest event has been in the batch for more than maxBatchDelayMsec milliseconds.
maxBatchDelayMsec number of milliseconds No Specifies the maximum time that events are held in a batch before the batch gets pushed through the pipeline to filters and outputs. The batch is pushed down when it reaches the maxEventBatchSize, or its oldest event has been in the batch for more than maxBatchDelayMsec milliseconds.
maxConcurrency number No Specifies the maximum number of threads that events can be processed. Each event will be processed by a single thread, by multiple threads can process different events simultaneously.
pipelineCompletionTimeoutMsec number of milliseconds No Specifies the timeout to wait for the pipeline to shutdown and clean up. The shutdown process starts when the DiagnosePipeline object is disposed, which usually happens on application exit.

Service Fabric Support

Nuget Package: Microsoft.Diagnostics.EventFlow.ServiceFabric

This package contains two components that make it easier to include EventFlow in Service Fabric applications: the ServiceFabricDiagnosticPipelineFactory and ServiceFabricHealthReporter. ServiceFabricHealthReporter is used automatically by ServiceFabricDiagnosticPipelineFactory. It does not require any configuration and does not need to be listed in the pipeline configuration file.

The ServiceFabricDiagnosticPipelineFactory is a replacement for the standard DiagnosticPipelineFactory, one that uses Service Fabric configuration support to load pipeline configuration. The resulting pipeline reports any execution problems through the Service Fabric health subsystem. The factory exposes a static Create() method that takes two parameters:

Parameter Default Value Description
healthEntityName (none) The name of the health entity that will be used to report EventFlow pipeline health to Service Fabric. Usually it is set to a value that helps you identify the service using the pipeline, for example "MyApplication-MyService-DiagnosticsPipeline".
configurationFileName "eventFlowConfig.json" The name of the configuration file that contains pipeline configuration. The file is expected to be part of a (Service Fabric) service configuration package.
configurationPackageName "Config" The name of the Service Fabric configuration package that contains the pipeline configuration file.

The recommended place to create the diagnostic pipeline is in the service Main() method:

public static void Main(string[] args)
{
    try
    {
        using (ManualResetEvent terminationEvent = new ManualResetEvent(initialState: false))
        using (var diagnosticsPipeline = ServiceFabricDiagnosticPipelineFactory.CreatePipeline("MyApplication-MyService-DiagnosticsPipeline"))
        {
            Console.CancelKeyPress += (sender, eventArgs) => Shutdown(diagnosticsPipeline, terminationEvent);

            AppDomain.CurrentDomain.UnhandledException += (sender, unhandledExceptionArgs) =>
            {
                ServiceEventSource.Current.UnhandledException(unhandledExceptionArgs.ExceptionObject?.ToString() ?? "(no exception information)");
                Shutdown(diagnosticsPipeline, terminationEvent);
            };

            ServiceRuntime.RegisterServiceAsync("MyServiceType", ctx => new MyService(ctx)).Wait();

            ServiceEventSource.Current.ServiceTypeRegistered(Process.GetCurrentProcess().Id, typeof(MyService).Name);

            terminationEvent.WaitOne();
        }
    }
    catch (Exception e)
    {
        ServiceEventSource.Current.ServiceHostInitializationFailed(e.ToString());
        throw;
    }    
}

private static void Shutdown(IDisposable disposable, ManualResetEvent terminationEvent)
{
    try
    {
        disposable.Dispose();
    }
    finally
    {
        terminationEvent.Set();
    }
}

The purpose of handling CancelKeyPress and UnhandledException events (the latter for full .NET Framework only) is to ensure that the EventFlow pipeline is cleanly disposed. This is important for pipeline elements that rely on system-level resources. For example, Event Tracing for Windows (ETW) input creates a system-wide ETW listening session, which must be disposed when the EventFlow pipeline is shut down. Ctrl-C signal is the standard way the Service Fabric runtime uses to notify service processes that they need to perform cleanup and exit. By default the process has 30 seconds to react.

The UnhandledException event method is a very simple addition to the standard ServiceEventSource:

    [Event(UnhandledExceptionEventId, Level = EventLevel.Error, Message = "An unhandled exception has occurred")]
    public void UnhandledException(string exception)
    {
       WriteEvent(UnhandledExceptionEventId, exception);
    }

Support for Service Fabric settings and application parameters

Version 1.0.1 of the EventFlow Service Fabric NuGet package introduced the ability to refer to Service Fabric settings from EventFlow configuration using special syntax for values:

servicefabric:/<section-name>/<setting-name>

where <section-name> is the name of Service Fabric configuration section and <setting-name> is the name of the Service Fabric configuration setting that is providing the value for some EventFlow setting. For example:

"basicAuthenticationUserPassword": "servicefabric:/DiagnosticPipelineParameters/ElasticSearchUserPassword"

The EventFlow configuration entry above means "take the ElasticSearchUserPassword setting from DiagnosticPipelineParameters section of the Service Fabric service configuration and use its value as the value for the EventFlow basicAuthenticationUserPassword setting". As with other Service Fabric settings, the values can also be overriden by Service Fabric application parameters. For more information on this see Manage application parameters for multiple environments topic in Service Fabric documentation.

Version 1.1.2 added support for resolving paths to other configuration files that are part of the default service configuration package. The syntax is:

servicefabricfile:/<configuration-file-name>

At run time this value will be substituted with a full path to the configuration file with the given name. This is especially useful if an EventFlow pipeline element wraps an existing library that has its own configuration file format (as is the case with Application Insights, for example).

Logical Expressions

The logical expression allows you to filter events based on the event properties. For example, you can have an expression like ProviderName == MyEventProvider && EventId == 3, where you specify the event property name on the left side and the value to compare on the right side. If the value on the right side contains special characters, you can enclose it in double quotes.

Standard and custom (payload) properties are treated equally; there is no need to prefix custom properties in any way. For example, expression TenantId != Unknown && ProviderName == MyEventProvider will evaluate to true for events that

  • were created by MyEventProvider provider (ProviderName is a standard property available for all events), and
  • have a TenantId custom property, with value that is different from "Unknown" string.

Operators supported by logical expressions are:

Comparison: ==, !=, <, >, <=, >=

Bitwise Equality: &== (true if bit mask is set, i.e., (lhsValue & rhsValue) == rhsValue, this is useful when filter on properties like Keywords)

Regular Expression: ~= (provide a regular expression pattern on the right)

Logical: &&, ||, ! (the precedence is ! > && > ||)

Grouping: (expression) (grouping can be used to change the evaluation order of expressions with logical operators)

Store Secret Securely

If you don't want to put sensitive information in the EventFlow configuration file, you can store the information at a secured place and pass it to the configuration at run time. Here is the sample code:

string configFilePath = @".\eventFlowConfig.json";
IConfiguration config = new ConfigurationBuilder().AddJsonFile(configFilePath).Build();
IConfiguration eventHubOutput = config.GetSection("outputs").GetChildren().FirstOrDefault(c => c["type"] == "EventHub");

if (eventHubOutput != null)
{
    string eventHubConnectionString = GetEventHubConnectionStringFromSecuredPlace();
    eventHubOutput["connectionString"] = eventHubConnectionString;
}

using (DiagnosticPipeline pipeline = DiagnosticPipelineFactory.CreatePipeline(config))
{
    // ...
}

Extensibility

Every pipeline element type (input, filter, output and health reporter) is a point of extensibility, that is, custom elements of these types can be used inside the pipeline. Contracts for all EventFlow element types are provided by EventFlow.Core assembly (except from the input type, see below).

EventData class

EventFlow pipelines operate on EventData objects. Each EventData object represents a single telemetry record (event) and has the following public properties and methods:

Name Type Description
Timestamp DateTimeOffset Indicates time when the event was created.
ProviderName string Identifies the source of the event.
Level LogLevel (enumeration) Provides basic severity assesment of the event: is it a critical error, regular error, a warning, etc.
Keywords long Provides means to efficiently classify events. The field is supposed to be interpreted as a set of bits (64 bits available). The meaning of each bit is specific to the event provider; EventFlow does not interpret them in any way.
Payload IDictionary<string, object> Stores event properties
TryGetMetadata(string kind, out IReadOnlyCollection<EventMetadata> metadata) bool Retrieves metadata of a given kind (if any) from the event. Returns true if metadata of given kind was found, otherwise false.
SetMetadata(EventMetatada metadata) void Adds (attaches) a new piece of metadata to the event.
GetValueFromPayload<T>(string name, ProcessPayload<T> handler) bool Retrieves a payload value from the payload (set of event properties). Although the payload can be accessed directly via Payload property, this method is useful because it will check whether the property exists and perform basic type conversion as necessary.
AddPayloadProperty(string key, object value, IHealthReporter healthReporter, string context) void Adds a new payload property to the event, performing property name disambiguation as necessary. The healthReporter and context parameters are used to produce a warning in case the name disambiguation is necessary (had to be changed because the event already had a property with name equal to key parameter).
DeepClone() EventData Performs a deep clone operation on the EventData. The resulting copy is independent from the original and either can be modified without affecting the other (e.g. properties or metadata can be added or removed). The only exception is that payload values are not cloned (and thus are shared between the copies).

Note that EventData type is not thread-safe. Don't try to use it concurrently from multiple threads.

EventFlow pipeline element types

Inputs

Inputs are producing new events (EventData instances). Anything that implements IObservable<EventData> can be used as an input for EventFlow. IObservable<T> is a standard .NET interface in the System namespace.

Filters

Filters have a dual role: they modify events (e.g. by decorating them with metadata) and instruct EventFlow to keep or discard the event. They are expected to implement the IFilter interface:

public enum FilterResult
{
    KeepEvent = 0,
    DiscardEvent = 1
}
public interface IFilter
{
    FilterResult Evaluate(EventData eventData);
}

Outputs

Output's purpose is to send data to its final destination. It is expected to implement IOutput interface:

public interface IOutput
{
    Task SendEventsAsync(IReadOnlyCollection<EventData> events, long transmissionSequenceNumber, CancellationToken cancellationToken);
}

The output receives a batch of events, along with transmission sequence number and a cancellation token. The transmission sequence number can be treated as an identifier for the SendEventsAsync() method invocation; it is guaranteed to be unique for each invocation, but there is no guarantee that there will be no "gaps", nor that it will be strictly increasing. The cancellation token should be used to cancel long-running operations if necessary; typically it is passed as a parameter to asynchronous i/o operations.

Pipeline structure and threading considerations

Every EventFlow pipeline can be created imperatively, i.e. in the program code. The structure of every pipeline is reflected in the constructor of the DiagnosticPipeline class and is as follows:

  1. One or more inputs produce events.
  2. A set of common filters (also known as 'global' filters) does initial filtering.
  3. Then the events are sent to one or more outputs (by cloning them as necessary). Each output can have its own set of filters. A combination of an output and a set of filters associated with that output is called a 'sink'.

EventFlow employs the following policies with regards to concurrency:

  1. Inputs are free to call OnNext() on associated observers using any thread.
  2. EventFlow will ensure that only one filter at a time is evaluating any given EventData object. That said, the same filter can be invoked concurrently for different events.
  3. Outputs will invoked concurrently for different batches of data.

Using custom pipeline items imperatively

The simplest way to use custom EventFlow elements is to create a pipeline imperatively, in code. You just need to create a read-only collections of the inputs, global filters and sinks and pass them to DiagnosticPipeline constructor. Custom and standard elements can be combined freely; each of the standard pipeline elements has a public constructor and associated public configuration class and can be created imperatively.

Creating a pipeline with custom elements using configuration

To create an EventFlow pipeline with custom elements from configuration each custom element needs a factory. The factory is an object implementing IPipelineItemFactory<TPipelineItem> and is expected to have a parameter-less constructor.

The factory's CreateItem(IConfiguration configuration, IHealthReporter healthReporter) method will receive a configuration fragment that represents the pipeline item being created. The health reporter is available to report issues in case configuration is corrupt or some other problem occurrs during item creation. The health reporter can also be passed to and used by the created pipeline item.

For EventFlow to know about the item factory it must appear in the 'extensions' section of the configuration file. Each extension record has 3 properties:

  1. "category" identifies extension type. Currently types recognized by DiagnosticPipelineFactory are inputFactory, filterFactory, outputFactory or healthReporter.
  2. "type" is the tag that identifies the extension in other parts of the configuration document(s). It is totally up to the user of an extension what she uses here.
  3. "qualifiedTypeName" is the string that allows DiagnosticPipelineFactory to instantiate the extension factory

Here is a very simple example that illustrates how to create a custom output and instantiate it from a configuration file.

namespace EventFlowCustomOutput
{
    class Program
    {
        static void Main(string[] args)
        {
            using (DiagnosticPipelineFactory.CreatePipeline("eventFlowConfig.json"))
            {
                Trace.TraceError("Hello, world!");
                Thread.Sleep(1000);
            }
        }
    }

    class CustomOutput : IOutput
    {
        public Task SendEventsAsync(IReadOnlyCollection<EventData> events, long transmissionSequenceNumber, CancellationToken cancellationToken)
        {
            foreach(var e in events)
            {
                Console.WriteLine($"CustomOutput: event says '{e.Payload["Message"]?.ToString() ?? "nothing"}'");
            }
            return Task.CompletedTask;
        }
    }

    class CustomOutputFactory : IPipelineItemFactory<CustomOutput>
    {
        public CustomOutput CreateItem(IConfiguration configuration, IHealthReporter healthReporter)
        {
            return new CustomOutput();
        }
    }
}

(content of eventFlowConfig.json)

{
  "inputs": [
    {
      "type": "Trace"
    }
  ],
  "filters": [
  ],
  "outputs": [
    {
      "type":  "CustomOutput"
    }
  ],
  "schemaVersion": "2016-08-11",

  "extensions": [
    {
      "category": "outputFactory",
      "type": "CustomOutput",
      "qualifiedTypeName": "EventFlowCustomOutput.CustomOutputFactory, EventFlowCustomOutput"
    }
  ]
}

Platform Support

EventFlow supports full .NET Framework (.NET 4.5 series and 4.6 series) and .NET Core, but not all inputs and outputs are supported on all platforms. The following table lists platform support for standard inputs and outputs.

Input Name .NET 4.5.1 .NET 4.6 .NET Core
Inputs
System.Diagnostics.Trace Yes Yes Yes
EventSource No Yes Yes
PerformanceCounter Yes Yes No
Serilog Yes Yes Yes
Microsoft.Extensions.Logging Yes Yes Yes
ETW (Event Tracing for Windows) Yes Yes No
Application Insights input Yes Yes Yes
Outputs
StdOutput (console output) Yes Yes Yes
Application Insights Yes Yes Yes
Azure EventHub Yes Yes Yes
Elasticsearch Yes Yes Yes
OMS (Operations Management Suite) Yes Yes Yes

Contributions

Refer to contribution guide.

Code of Conduct

Refer to Code of Conduct guide.