chore(serverless): emit MicroVM request start for WSGI & ASGI-based applications

[litianningdatadog]

Stacked PRs:

• chore(runtime): add explicit identity refresh #19778 — runtime identity foundation
  • 👉 This PR chore(serverless): emit MicroVM request start for WSGI & ASGI-based applications #19898 — WSGI/ASGI request-start hook
    • feat(runtime): refresh MicroVM identity #19939 — central MicroVM /run identity refresh
      • chore(tracer): tracer/writer identity refresh and stale-buffer reset #19820 — tracer/native writer exporter refresh
        • fix(telemetry): rebuild worker on identity refresh #19821 — telemetry worker refresh
          • chore(runtime): refresh runtime metric identity and collector state #19822 — runtime metrics runtime-id tags

Description

MicroVMs call the language runtime through a local /run endpoint before the user request is served. The identity refresh stack needs a request-start signal before the framework root span is created; otherwise the first span for a fresh MicroVM run can still pick up the previous runtime ID.

The WSGI and ASGI entry points now recognize the AWS Lambda MicroVM runtime request and emit the existing web.request.starting event before root-span creation. Normal application requests, non-MicroVM environments, and non-matching paths keep the old behavior.

Path construction is deferred until after the POST and MicroVM-environment checks, so ordinary non-POST requests avoid the additional path normalization and concatenation.

The WSGI/Django paths also now:

• dispatch from automatically instrumented Django WSGI requests, which bypass the generic WSGI middleware;
• coalesce nested WSGI and Django middleware so one runtime request emits one event; and
• mark the request only after a matching event was actually dispatched.

Reference

• RFC

Testing

Added focused WSGI, ASGI, Django WSGI, and runtime-detection coverage for:

• dispatching web.request.starting for the MicroVM runtime request;

• preserving normal request behavior;

• mounted and full-path WSGI/ASGI path representations;

• skipping the MicroVM environment check for non-POST requests;

• dispatching the request event before span creation in both WSGI and ASGI middleware;

• preventing duplicate dispatch through nested WSGI middleware and Django WSGI instrumentation; and

• MicroVM environment detection for set, unset, and whitespace-only values.

• ASGI-based Django test shows the run event can be intercepted

- WSGI-based Flask [test](https://us-east-2.console.aws.amazon.com/cloudwatch/home?region=us-east-2#logsV2:log-groups/log-group/$252Faws$252Flambda-microvms$252Fsample-flask-app/log-events/2026$252F09$252F04$255B18.0$255Dmicrovm-672def42-7c09-3b3d-a1cf-a6bff1be0e64$3FfilterPattern%3DMicroVM%26start%3D1788494400000%26end%3D1788580799000) shows the run event can be intercepted

Validation:

• scripts/lint fmt
• scripts/lint style
• scripts/lint typing
• focused ASGI hook tests: 48 passed
• focused WSGI hook tests: 7 passed
• MicroVM detector tests: 3 passed
• focused WSGI regression test: 1 passed in venv 13873ec
• focused Django WSGI regression tests: 2 passed in venv 7e85837

Risks

Low. The new event is limited to AWS Lambda MicroVM runtime metadata and leaves non-matching ASGI/WSGI requests unchanged. This PR is internal plumbing; customer-facing release-note content belongs with follow-up PR #19939.

[cit-pr-commenter-54b7da]

Codeowners resolved as

Resolved from the full PR diff against tianning.li/1-runtime-identity-refresh using the target branch CODEOWNERS file.
CODEOWNERS team requests not listed below are not required by the current file set.

ddtrace/contrib/_events/web_framework.py                                @DataDog/python-guild @DataDog/apm-idm-python
ddtrace/contrib/internal/asgi/middleware.py                             @DataDog/python-guild @DataDog/apm-idm-python
ddtrace/contrib/internal/django/response.py                             @DataDog/python-guild @DataDog/apm-idm-python
ddtrace/contrib/internal/web.py                                         @DataDog/python-guild @DataDog/apm-idm-python
ddtrace/contrib/internal/wsgi/wsgi.py                                   @DataDog/python-guild @DataDog/apm-idm-python
ddtrace/internal/constants.py                                           @DataDog/apm-core-python
ddtrace/internal/serverless/__init__.py                                 @DataDog/apm-core-python
tests/contrib/asgi/test_asgi.py                                         @DataDog/python-guild @DataDog/apm-idm-python
tests/contrib/django/test_django.py                                     @DataDog/python-guild @DataDog/apm-idm-python
tests/contrib/wsgi/test_wsgi.py                                         @DataDog/python-guild @DataDog/apm-idm-python
tests/internal/test_serverless.py                                       @DataDog/apm-serverless @DataDog/asm-python @DataDog/serverless-aws @DataDog/serverless-azure-and-gcp

[cit-pr-commenter-54b7da]

Circular import analysis

⚠️ Existing circular imports

There are 1 circular imports that already exist on the base branch and have not been changed by this PR.

ddtrace.errortracking._handled_exceptions.bytecode_injector -> ddtrace.errortracking._handled_exceptions.callbacks -> ddtrace.errortracking._handled_exceptions.collector -> ddtrace.errortracking._handled_exceptions.bytecode_reporting -> ddtrace.errortracking._handled_exceptions.bytecode_injector

[cit-pr-commenter-54b7da]

Dependency direction analysis

⚠️ Existing dependency direction violations

There are 205 dependency direction violations that already exist on the base branch and have not been changed by this PR.

Show existing violations (showing 5 of 205 highest severity)

ddtrace.internal.tracemethods -×-> ddtrace.trace  (internal-core -> product:tracing, score=132)
ddtrace.appsec._listeners -×-> ddtrace.trace  (product:appsec -> product:tracing, score=130)
ddtrace.internal.ci_visibility.recorder -×-> ddtrace.trace  (product:ci_visibility -> product:tracing, score=130)
ddtrace.profiling.collector.pytorch -×-> ddtrace.trace  (product:profiling -> product:tracing, score=130)
ddtrace.debugging._signal.tracing -×-> ddtrace.trace  (product:debugging -> product:tracing, score=130)

To see all violations, download the layers-base.json and layers-pr.json artifacts from this CI job and run:

uv run --script scripts/import-analysis/layers.py compare layers-base.json layers-pr.json

[datadog-datadog-us1-prod]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 7398b18 | Docs | View more details | Give us feedback!}

[Copilot]

🟡 Changes recommended

The environment detector lacks direct coverage, and the release note announces behavior completed only by a follow-up PR.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Adds pre-span MicroVM request detection to WSGI and ASGI instrumentation, supporting the runtime identity refresh stack.

Changes:

• Dispatches web.request.starting for matching MicroVM requests.
• Adds explicit runtime identity refresh callbacks while preserving fork lineage.
• Adds focused integration/runtime tests and a release note.

File summaries

File	Description
ddtrace/contrib/_events/web_framework.py	Defines the request-start event.
ddtrace/contrib/internal/web.py	Matches and dispatches MicroVM requests.
ddtrace/contrib/internal/asgi/middleware.py	Dispatches before ASGI span creation.
ddtrace/contrib/internal/wsgi/wsgi.py	Dispatches before WSGI span creation.
ddtrace/internal/serverless/__init__.py	Detects the MicroVM environment.
ddtrace/internal/runtime/__init__.py	Adds explicit identity refresh support.
tests/contrib/asgi/test_asgi.py	Tests ASGI matching and ordering.
tests/contrib/wsgi/test_wsgi.py	Tests WSGI request matching.
tests/tracer/runtime/test_runtime_id.py	Tests refresh and fork semantics.
releasenotes/notes/add-lambda-microvm-web-request-starting-ffa6841a15e3c57c.yaml	Announces MicroVM request detection.

Review details

• Files reviewed: 8/8 changed files
• Comments generated: 2
• Review effort level: Balanced

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[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-23T18:53:55.747647Z	24e4d34	Draft marked ready
🔒 Security Review	✅ Completed 2026-09-23T18:50:33.781425Z	24e4d34	Draft marked ready

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[jcstorms1]

Just looked at the files we own. LGTM