This Serilog sink transforms Serilog events into OpenTelemetry LogRecord
s and sends them to an OTLP (gRPC or HTTP) endpoint.
The sink aims for full compliance with the OpenTelemetry Logs protocol. It does not depend on the OpenTelemetry SDK or .NET API.
OpenTelemetry supports attributes with scalar values, arrays, and maps. Serilog does as well. Consequently, the sink does a one-to-one mapping between Serilog properties and OpenTelemetry attributes. There is no flattening, renaming, or other modifications done to the properties by default.
To use the OpenTelemetry sink, first install the NuGet package:
dotnet add package Serilog.Sinks.OpenTelemetry
Then enable the sink using WriteTo.OpenTelemetry()
:
Log.Logger = new LoggerConfiguration() .WriteTo.OpenTelemetry() .CreateLogger();
Generate logs using the Log.Information(...)
and similar methods to send transformed logs to a local OpenTelemetry OTLP endpoint.
A more complete configuration would specify Endpoint
, Protocol
, and other parameters, such asResourceAttributes
, as shown in the examples below.
This sink supports two configuration styles: inline and options. Inline configuration is appropriate for simple, local logging setups, and looks like:
Log.Logger = new LoggerConfiguration() .WriteTo.OpenTelemetry( endpoint: "http://127.0.0.1:4318", protocol: OtlpProtocol.HttpProtobuf) .CreateLogger();
More complicated use cases need to use options-style configuration, which looks like:
Log.Logger = new LoggerConfiguration() .WriteTo.OpenTelemetry(options => { options.Endpoint = "http://127.0.0.1:4318"; options.Protocol = OtlpProtocol.HttpProtobuf; }) .CreateLogger();
This supports the sink's full set of configuration options. See the OpenTelemetrySinkOptions.cs
file for the full set of options. Some of the more important parameters are discussed in the following sections.
The default endpoint and protocol are http://localhost:4317
and OtlpProtocol.Grpc
.
In most production scenarios, you'll need to set an endpoint and protocol to suit your deployment environment. To do so, add the endpoint
argument to the WriteTo.OpenTelemetry()
call.
You may also want to set the protocol. The supported values are:
OtlpProtocol.Grpc
: Sends a protobuf representation of the OpenTelemetry Logs over a gRPC connection (the default).OtlpProtocol.HttpProtobuf
: Sends a protobuf representation of the OpenTelemetry Logs over an HTTP connection.OpenTelemetry logs may contain a "resource" that provides metadata concerning the entity associated with the logs, typically a service or library. These may contain "resource attributes" and are emitted for all logs flowing through the configured logger.
These resource attributes may be provided as a Dictionary<string, Object>
when configuring a logger. OpenTelemetry allows resource attributes with rich values; however, this implementation only supports resource attributes with primitive values.
⚠️ Resource attributes with non-primitive values will be silently ignored.
This example shows how the resource attributes can be specified when the logger is configured.
Log.Logger = new LoggerConfiguration() .WriteTo.OpenTelemetry(options => { options.Endpoint = "http://127.0.0.1:4317"; options.ResourceAttributes = new Dictionary<string, object> { ["service.name"] = "test-logging-service", ["index"] = 10, ["flag"] = true, ["value"] = 3.14 }; }) .CreateLogger();Environment variable overrides
The sink also recognizes a selection of the OTEL_OTLP_EXPORTER_*
environment variables described in the OpenTelemetry documentation, and will override programmatic configuration with any environment variable values present at runtime.
To switch off this behavior, pass ignoreEnvironment: true
to the WriteTo.OpenTelemetry()
configuration methods.
LogEvent
to OpenTelemetry log record mapping
The following table provides the mapping between the Serilog log events and the OpenTelemetry log records.
SerilogLogEvent
OpenTelemetry LogRecord
Comments Exception.GetType().ToString()
Attributes["exception.type"]
Exception.Message
Attributes["exception.message"]
Ignored if empty Exception.StackTrace
Attributes[ "exception.stacktrace"]
Value of ex.ToString()
Level
SeverityNumber
Serilog levels are mapped to corresponding OpenTelemetry severities Level.ToString()
SeverityText
Message
Body
Culture-specific formatting can be provided via sink configuration MessageTemplate
Attributes[ "message_template.text"]
Requires IncludedData. MessageTemplateText
(enabled by default) MessageTemplate
(MD5) Attributes[ "message_template.hash.md5"]
Requires IncludedData. MessageTemplateMD5 HashAttribute
Properties
Attributes
Each property is mapped to an attribute keeping the name; the value's structure is maintained SpanId
(Activity.Current
) SpanId
Requires IncludedData.SpanIdField
(enabled by default) Timestamp
TimeUnixNano
.NET provides 100-nanosecond precision TraceId
(Activity.Current
) TraceId
Requires IncludedData.TraceIdField
(enabled by default) Configuring included data
This sink supports configuration of how common OpenTelemetry fields are populated from the Serilog LogEvent
and .NET Activity
context via the IncludedData
flags enum:
Log.Logger = new LoggerConfiguration() .WriteTo.OpenTelemetry(options => { options.Endpoint = "http://127.0.0.1:4317"; options.IncludedData: IncludedData.MessageTemplateTextAttribute | IncludedData.SpecRequiredResourceAttributes; }) .CreateLogger();
The example shows the default value; IncludedData.MessageTemplateMD5HashAttribute
can also be used to add the MD5 hash of the message template.
Serilog LogEvents
that carry a SpanStartTimestamp
property of type DateTime
will be recognized as spans by this sink, and sent using the appropriate OpenTelemetry endpoint and schema. The properties recognized by the sink match the ones emitted by SerilogTracing.
In addition to the field mapping performed for log records, events that represent trace spans can carry the special properties listed below.
SerilogLogEvent
OpenTelemetry Span
Comments MessageTemplate
Name
Properties["ParentSpanId"]
ParentSpanId
Value must be of type ActivitySpanId
Properties["SpanKind"]
Kind
Value must be of type ActivityKind
Properties["SpanStartTimestamp"]
StartTimeUnixNano
Value must be of type DateTime
; .NET provides 100-nanosecond precision Timestamp
EndTimeUnixNano
.NET provides 100-nanosecond precision Suppressing other instrumentation
If the sink is used in an application that also instruments HTTP or gRPC requests using the OpenTelemetry libraries, this can be suppressed for outbound requests made by the sink using OnBeginSuppressInstrumentation
:
Log.Logger = new LoggerConfiguration() .WriteTo.OpenTelemetry(options => { options.OnBeginSuppressInstrumentation = OpenTelemetry.SuppressInstrumentationScope.Begin; // ...
The example/Example
subdirectory contains an example application that logs to a local OpenTelemetry collector. See the README in that directory for instructions on how to run the example.
In .NET 5 and later versions, the Activity.DefaultIdFormat
is ActivityIdFormat.W3C
. In previous versions, the default format is ActivityIdFormat.Hierarchical
. To make use of the Activity's traces and spans, you should set the global Activity.DefaultIdFormat
to ActivityIdFormat.W3C
in .NET Framework environments. Read more: Default ActivityIdFormat is W3C
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