Application Diagnostics in .NET Core 3.1

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Application Diagnostics in .NET Core 3.1 David Fowler – ASP.NET Architect @davidfowl Damian Edwards – ASP.NET Program Manager @damianedwards

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.NET diagnostics primitives • Events • This thing happened, here’s a message and some data associated with it, e.g. Request started, path: /test, query: a=b • Metrics • Here’s a number representing the current state of this thing, e.g. Requests per second: 4, CPU utilization: 36%, ThreadPool queue length: 3 • Dumps • Here’s the memory associated with the application process at a point in time, saved in a platform-specific file

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Producing diagnostics data • ILogger – structured logging abstraction, used in ASP.NET Core • DiagnosticSource – synchronous, in-process, live objects (untyped) • Activity – auto-flowing, ephemeral diagnostics context, dist. tracing • Runtime events – details from the CLR • EventSource – produce events & metrics, built-in

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ILogger

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DiagnosticSource

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EventSource

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Collecting diagnostics data • EventListener API • DiagnosticListener API • EventPipe API • EventPipe – default “on” out-of-process diagnostics server • Effectively “ETW for .NET” that works cross-platform • dotnet CLI tools • dotnet-counters: Collect & view counters • dotnet-trace: Collect & convert events • dotnet-dump: Collect a process dump • dotnet-gcdump: Collect a managed heap dump • dotnet-sos: Installs SOS and configures LLDB for dump debugging • dotnet-symbol: Downloads symbols files for dump debugging

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EventListener

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DiagnosticsListener

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EventPipe API

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Demo: CLI tools

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Scenarios

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Distributed tracing • Logs share trace IDs across HTTP calls between ASP.NET Core apps by default in 3.0 • Support for W3C Trace Context • The OpenTelemetry SDK supports ASP.NET Core • Visualize with tools such as Prometheus, Jaeger, Zipkin, and Application Insights