[dotnet] Raise ThreadPool min threads to avoid Kestrel stalls

[NachoEchevarria]

Motivation

Test_SqlServiceNameSource intermittently fails in INTEGRATIONS (~2% of runs in dd-trace-dotnet master). Root cause: Kestrel response-flush stalls for ~5 s while the .NET ThreadPool grows — the request completes server-side in ~12 ms, but bytes don't reach the client until after the test's 5 s read timeout.

The ThreadPool defaults its minimum to Environment.ProcessorCount for both worker and IOCP threads (so 2–4 on ubuntu-latest), and grows by 1 thread every ~500 ms. Under cumulative tracer + AppSec + IAST background load in this scenario, Kestrel's I/O queues behind tracer activity until the pool grows — long enough to trip the client timeout.

Changes

Set DOTNET_ThreadPool_ForceMinWorkerThreads=32 and DOTNET_ThreadPool_ForceMinIoCompletionThreads=32 in poc.Dockerfile and uds.Dockerfile. 32 is a comfortable floor above the burst; idle threads cost ~1 MB each, and on hosts with ≥32 vCPU the env vars are a no-op.

Verification

2 CI runs × 50 INTEGRATIONS attempts = 100 fresh scenario runs, 0 stalls (prior baseline ≈ 2 / 100). Diagnostic branch diag/dotnet-rasp-sqli-stall kept in case the flake reappears.

[github-actions]

CODEOWNERS have been resolved as:

utils/build/docker/dotnet/poc.Dockerfile                                @DataDog/apm-dotnet @DataDog/asm-dotnet @DataDog/system-tests-core
utils/build/docker/dotnet/uds.Dockerfile                                @DataDog/apm-dotnet @DataDog/asm-dotnet @DataDog/system-tests-core

[Copilot]

Pull request overview

This PR aims to eliminate intermittent .NET integration test flakes caused by Kestrel response flush delays while the .NET ThreadPool ramps up under tracer/AppSec/IAST load, by forcing higher minimum ThreadPool worker and I/O completion thread counts in the Docker images used for these scenarios.

Changes:

• Set DOTNET_ThreadPool_ForceMinWorkerThreads=32 in the .NET Docker runtime images used by the tests.
• Set the I/O completion thread minimum via a DOTNET_ThreadPool_ForceMin*CompletionThreads environment variable in the same images.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
utils/build/docker/dotnet/uds.Dockerfile	Adds ThreadPool minimum thread environment variables to reduce Kestrel stalls in UDS scenario images.
utils/build/docker/dotnet/poc.Dockerfile	Adds ThreadPool minimum thread environment variables to reduce Kestrel stalls in PoC scenario images.

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[andrewlock]

Worth a try, thanks!