Serilog.Sinks.OpenTelemetry

⚠️ Prototype implementation. Do not use for production!

This Serilog sink will transform Serilog events into OpenTelemetry LogRecords and send them to an OpenTelemetry gRPC endpoint.

OpenTelemetry attributes support for 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 properies by default.

The formatter renders the log message, which is then stored as the body of the OpenTelemetry LogRecord.

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():

var log = new LoggerConfiguration()
    .WriteTo.OpenTelemetry()
    .CreateLogger();

Then use the Log.Information(...) and similar methods to send transformed logs to a local OpenTelemetry (OTLP/gRPC) endpoint.

A more complete configuration would specify the endpoint and resourceAttributes.

Endpoint

The default endpoint is http://localhost:4317/v1/logs, which will send logs to an OpenTelemetry collector running on the same machine. This is appropriate for testing or for using a local OpenTelemetry collector as a proxy for a downstream logging service.

In most production scenarios, you will want to set an endpoint. To do so, add the endpoint argument to the WriteTo.OpenTelemetry() call. This must be a full URL to an OTLP/gRPC endpoint.

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. While 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.

var log = new LoggerConfiguration()
    .MinimumLevel.Information()
    .WriteTo.OpenTelemetry(endpoint: "http://127.0.0.1:4317/v1/logs",
    resourceAttributes: new Dictionary<String, Object>() {
            {"service.name", "test-logging-service"},
            {"index", 10},
            {"flag", true},
            {"value", 3.14}
        })
    .CreateLogger();

Serilog Log Events to OpenTelemetry Logs Transformation

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

Serilog (LogEvent)	OpenTelemetry (LogRecord)	Comment
Properties	Attributes[*]	Each property is mapped to an attribute keeping the name. The value's structure is maintained.
Timestamp	Field[TimeUnixNano]	Serilog provides only millisecond precision
MessageTemplate (rendered)	Field[Body]	Any formatter can be provided via sink configuration
MessageTemplate	Attribute[serilog.message.template]
MessageTemplate (hash)	Attribute[serilog.message.hash]
Level	Field[SeverityText]	Direct copy of value
Level	Field[SeverityNumber]	Serilog levels mapped into corresponding OpenTelemetry levels
Exception	Attribute[exception.type]	Value of ex.GetType()
Exception	Attribute[exception.message]	Value of ex.Message, if not empty
Exception	Attribute[exception.stacktrace]	Value of ex.ToString()

Trace Context Enrichment

OpenTelemetry allows a TraceID and SpanID to be added to log records to associate a log with a particular request. Within .NET, these are found in the current activity.

If the WithTraceIdAndSpanId enricher is enabled and if the logging call takes place within an activity, the trace ID and span ID will be extracted from the activity and added to the Serilog LogEvent properties (and then into the OpenTelemetry LogRecord).

var log = new LoggerConfiguration()
    .Enrich.WithTraceIdAndSpanId()
    .WriteTo.OpenTelemetry()
    .CreateLogger();

Activity.Current	LogEvent Property	OpenTelemetry (LogRecord)	Comment
TraceId	traceId	Field[traceID]	Direct binary conversion maintains fidelity
SpanId	spanId	Field[spanID]	Direct binary conversion maintains fidelity

Although designed to be used with the OpenTelemetry sink, the enricher may be also useful when using other sinks.

Example

The test/Serilog.Sinks.OpenTelemetry.Example subdirectory contains an example application that logs to a local OpenTelemetry collector. See the README in that directory for instructions on running the example.

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