Serilog.Sinks.OpenTelemetry

This Serilog sink transforms Serilog events into OpenTelemetry LogRecords 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.

Getting started

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.

Configuration

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/v1/logs",
        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/v1/logs";
        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.

Endpoint and protocol

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.

Resource attributes

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.

Serilog LogEvent to OpenTelemetry log record mapping

The following table provides the mapping between the Serilog log events and the OpenTelemetry log records.

Serilog LogEvent	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.SpanId (enabled by default)
Timestamp	TimeUnixNano	.NET provides 100-nanosecond precision
TraceId (Activity.Current)	TraceId	Requires IncludedData.TraceId (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.MessageTemplate |
                              IncludedData.TraceId | IncludedData.SpanId;
    })
    .CreateLogger();

The example shows the default value; IncludedData.MessageTemplateMD5HashAttribute can also be used to add the MD5 hash of the message template.

Sending traces through the sink

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.

Serilog LogEvent	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

Example

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.

Copyright © Serilog Contributors - Provided under the Apache License, Version 2.0.