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configuration.md

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Configuration

By default, Correlator is configured following way:

  • Accepting Correlation ID from following headers (in order):
    • X-Correlation-Id
    • X-Request-Id
    • Request-Id (set by ASP.NET when sending request with HttpClient)
  • Correlation ID is forwarded to subsequent requests as X-Correlation-Id (when using CorrelatorHttpMessageHandler)
  • Correlation ID is not set to HTTP response headers
  • Correlation ID does not replace HttpContext.TraceIdentifier
  • Correlation ID is not added to logger scope
  • Correlation logging scope is (after enabling) "Correlation"

Adjusting default configuration

To adjust setting, use AddDefaultCorrelator or AddCorrelator overload:

services.AddDefaultCorrelator(
    correlatorOptions =>
    {
        // disable correlation ID factory
        // - correlation ID won't be generated
        // --> if correlation ID not received, empty value is used
        correlatorOptions.Factory = null;

        // expect correlation ID in "X-CID" header only
        // (clearing default headers first, then adding single entry)
        correlatorOptions.ReadFrom.Clear();
        correlatorOptions.ReadFrom.Add("X-CID");

        // return correlation ID in response, use custom header
        correlatorOptions.Emit = PropagationSettings.PropagateAs("X-RID");

        // forward via message handler
        // - when correlation ID received, using same header name ("X-CID")
        // - when correlation ID not received and generated, sending it with default header
        correlatorOptions.Forward = PropagationSettings.KeepIncomingHeaderName();

        // replace `HttpContext.TraceIdentifier`
        ReplaceTraceIdentifier = true,

        // create logging scope with default key
        LoggingScope = LoggingScopeSettings.IncludeLoggingScope(),
    });

Correlation ID factory (function)

Property CorrelatorOptions.Factory, of type Func<HttpContext, CorrelationId>.

If set to null, generating of correlation ID is disabled.

// default
correlatorOptions.Factory =
    (_) => CorrelationId.FromString(Guid.NewGuid().ToString("D"));

// custom (don't try this at home!)
correlatorOptions.Factory =
    (_) => CorrelationId.FromString("hello world!");

// disable generating
correlatorOptions.Factory = null;

Read from headers

Property CorrelatorOptions.ReadFrom, of type ICollection<string>.

First header satisfying match is read. Collection must not be empty.

// add after default headers
correlatorOptions.Add("X-Yet-Another-Request-ID");

// read only from given header
correlatorOptions.Clear();
correlatorOptions.Add("X-This-Is-Only-Possible-Correlation-ID-Now");

If you are sure about correlation header name, feel free to use just that and avoid unnecessary lookup in request headers.

Correlation ID propagation

There are two directions to propagate correlation ID:

  1. CorrelatorOptions.Emit: Return correlation ID within response headers
  2. CorrelatorOptions.Forward: Forward correlation ID to subsequent requests using CorrelatorHttpMessageHandler

No propagation

Correlation ID is not set.

// don't expose correlation ID in HTTP response
correlatorOptions.Emit = PropagationSettings.NoPropagation;

// don't forward correlation ID to subsequent requests
correlatorOptions.Forward = PropagationSettings.NoPropagation;

Use incoming header name

Correlation ID is propagated with same header name as it was read from.

// if correlation was taken from 'X-My-Custom-Correlation-Id', it is exposed with same header
correlatorOptions.Emit = PropagationSettings.KeepIncomingHeaderName();
correlatorOptions.Forward = PropagationSettings.KeepIncomingHeaderName();

Notice argument of KeepIncomingHeaderName(string). When Correlation ID is not received, there's obviously no way how to determine incoming header - and this is the place where you can help Correlator to know how to propagate correlation.

Default value of fallback header name is "X-Correlation-Id".

Predefined header name

Correlation ID is propagated with predefined header name.

// no matter how we got Correlation ID, it is exposed as 'X-Correlation-Id'
correlatorOptions.Emit = PropagationSettings.PropagateAs("X-Correlation-Id");
correlatorOptions.Forward = PropagationSettings.PropagateAs("X-Correlation-Id");

Replace Trace Identifier

Property ReplaceTraceIdentifier, of type bool.

Indicates whether received/generated correlation ID should overwrite ASP.NET Trace Identifier.

Logging scope

Property LoggingScope, of type LoggingScopeSettings.

Either:

  • NoScope: logging scope is not created
  • IncludeLoggingScope(string): logging scope is created, correlation ID is saved with provided key

Use scope for structured logging.

// no logging scope
correlatorOptions.LoggingScope = LoggingScopeSettings.NoScope;

// logging scope with: Correlation = <Correlation ID>
correlatorOptions.LoggingScope = LoggingScopeSettings.IncludeLoggingScope();

// logging scope with custom scope: CorrelationId = <Correlation ID>
correlatorOptions.LoggingScope = LoggingScopeSettings.IncludeLoggingScope("CorrelationId");

Silencing logger

If you find Correlator to be too chatty, you can always silence logging by:

{
  "Logging": {
    "LogLevel": {
      "Default": "Warning",
      "W4k.AspNetCore.Correlator": "None"
    }
  }
}

... or if you use Serilog:

Log.Logger = new LoggerConfiguration()
    .MinimumLevel.Override("W4k.AspNetCore.Correlator", LogEventLevel.Fatal);