Modern distributed tracing with dotnet

For any modern dotnet system, distributed tracing is already built in to the default web client, server, and other operations.

You can see this with a basic example, by configuring your logging to display the correlation identifier. Many logging systems, such as Elasticsearch, display correlation by default. The identifiers can also be passed across messaging, such as Azure Message Bus.

Logging has always been a useful way to understand what is happening within a system and for troubleshooting. However, modern systems are very complex, with multiple layers and tiers, including third party systems.

Trying to understand what has happened when a back end service log reports an error, and then correlating that to various messages and front end actions that triggered it requires some kind of correlation identifier.

This problem has existed ever since we have had commercial websites, for over 20 years of my career, with various custom solutions.

Finally, in 2020, a standard was created for the format of the correlation identifier, and how to pass the values: W3C Trace Context. In a very short amount of time all major technology providers have implemented solutions.

The examples below show how this is already implemented in modern dotnet.

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A Guide to W3C Trace Context

Earlier this year the W3C Trace Context Recommendation was finally published. A standard way of passing distributed trace correlation has been needed for a long time, and it is good to see there is finally a standard, and many vendors have already moved to adopt it.

The Recommendation defines what a distributed trace is:

A distributed trace is a set of events, triggered as a result of a single logical operation, consolidated across various components of an application. A distributed trace contains events that cross process, network and security boundaries. A distributed trace may be initiated when someone presses a button to start an action on a website - in this example, the trace will represent calls made between the downstream services that handled the chain of requests initiated by this button being pressed.

What constitutes a single logical operation depends on the system. In the example above it is a single button press on a website, whereas in a batch processing system it might be for each item processed, or in a complex UI it might consist of both a button press and a subsequent confirmation dialog.

The W3C Trace Context Recommendation describes how the correlation information — an identifier for the operation, and the parent-child relationships between components — is passed in service calls, but doesn't cover what to do with that information, apart from how to pass it to the next component.

This is a guide mostly how to use Trace Context for logging, although it also applies to metrics and other telemetry.

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