feat(aws-lambda-microvm): refresh identity on Flask run hook

[litianningdatadog]

Stacked PRs:

• chore(runtime): add explicit identity refresh #19778
  • chore(flask): emit MicroVM request-starting event #19816
    • chore(http_server): emit pre-request web event #19817
    • 👉🏽 This PR feat(aws-lambda-microvm): refresh identity on Flask run hook #19825
    • chore(remoteconfig): refresh client identity on runtime refresh #19818
      • chore(appsec): tag spans with refreshed rc client id #19819
    • fix(tracer): isolate MicroVM identity refresh #19820
    • fix(telemetry): rebuild worker on identity refresh #19821
    • chore(runtime): refresh runtime metric identity and collector state #19822
    • chore(crashtracking): reconfigure after identity refresh #19823
    • chore(symbol-db): refresh metadata after identity refresh #19824

Description

This is the Flask-only MicroVM /run activation path. When running inside an AWS Lambda MicroVM image, ddtrace registers a listener for the pre-request web event emitted by Flask. The listener matches the fixed platform hook:

POST /aws/lambda-microvms/runtime/v1/run

and calls runtime.refresh_identity() once per process. This keeps the activation path focused on Flask while the identity consumers are split across the 3-series draft PRs.

The hook registration is driven from ddtrace.__init__ after ddtrace.config is exported. ddtrace.internal.runtime imports the shared ddtrace.internal.core.event_names.WEB_REQUEST_STARTING constant and reuses ddtrace.internal.serverless.in_aws_lambda_microvm() for the environment check. This avoids importing ddtrace.contrib while ddtrace is partially initialized in MicroVM images.

Testing

• scripts/lint fmt ddtrace/__init__.py ddtrace/internal/runtime/__init__.py tests/tracer/runtime/test_runtime_id.py tests/contrib/flask/test_microvm_identity_refresh.py ddtrace/internal/serverless/__init__.py
• git diff --check
• uv run --script scripts/import-analysis/cycles.py analyze /tmp/ddtrace-cycles-pr19825.json
  • No cycle involving ddtrace.internal.runtime, ddtrace.internal.serverless, ddtrace.internal.settings, or ddtrace.contrib.internal.flask.patch; existing repository total remains 3.
• scripts/run-tests --venv 12c5734 -- -- tests/internal/test_serverless.py tests/tracer/runtime/test_runtime_id.py tests/contrib/flask/test_microvm_identity_refresh.py
  • Blocked locally during collection/build by the existing native-extension mismatch: ImportError: cannot import name 'process_metrics' from 'ddtrace.internal.native._native'

Stack

Depends on #19816.

Extracted from #19781 (closed)

[cit-pr-commenter-54b7da]

Codeowners resolved as

Resolved from the full PR diff against tianning.li/2-flask-web-request-starting-event using the target branch CODEOWNERS file.
CODEOWNERS team requests not listed below are not required by the current file set.

ddtrace/__init__.py                                                     @DataDog/python-guild
ddtrace/internal/runtime/__init__.py                                    @DataDog/apm-sdk-capabilities-python
releasenotes/notes/aws-lambda-microvm-identity-refresh-3a672cd6bcbad16d.yaml  @DataDog/apm-python
tests/contrib/flask/test_microvm_identity_refresh.py                    @DataDog/apm-core-python @DataDog/apm-idm-python
tests/tracer/runtime/test_runtime_id.py                                 @DataDog/apm-sdk-capabilities-python

[cit-pr-commenter-54b7da]

Circular import analysis

⚠️ Existing circular imports

There are 3 circular imports that already exist on the base branch and have not been changed by this PR.

ddtrace.llmobs -> ddtrace.llmobs._evaluators -> ddtrace.llmobs._evaluators.format -> ddtrace.llmobs._experiment -> ddtrace.llmobs
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
ddtrace.appsec._asm_request_context -> ddtrace.appsec._iast._iast_request_context_base -> ddtrace.appsec._iast._iast_env -> ddtrace.appsec._iast.reporter -> ddtrace.appsec._exploit_prevention.stack_traces -> ddtrace.appsec._asm_request_context

[cit-pr-commenter-54b7da]

Dependency direction analysis

📈 Existing violations got worse

10 pre-existing violation(s) increased in severity (e.g. their target became more depended-on, or got pulled into an import cycle), though the edge itself isn't new:

Show violations that got worse (showing 5 of 10 highest severity)

ddtrace.internal.writer.writer -×-> ddtrace.internal.runtime  (internal-core -> product:runtime, score=15, +1 vs base)
ddtrace.internal.symbol_db.remoteconfig -×-> ddtrace.internal.runtime  (internal-core -> product:runtime, score=15, +1 vs base)
ddtrace.internal.remoteconfig.client -×-> ddtrace.internal.runtime  (internal-core -> product:runtime, score=15, +1 vs base)
ddtrace.internal.telemetry.writer -×-> ddtrace.internal.runtime  (internal-core -> product:runtime, score=15, +1 vs base)
ddtrace.internal.core.crashtracking -×-> ddtrace.internal.runtime  (internal-core -> product:runtime, score=15, +1 vs base)

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

⚠️ Existing dependency direction violations

There are 250 dependency direction violations that already exist on the base branch and have not been changed by this PR.

Show existing violations (showing 5 of 250 highest severity)

ddtrace.internal.tracemethods -×-> ddtrace.trace  (internal-core -> product:tracing, score=135)
ddtrace.aiguard._api_client -×-> ddtrace.trace  (product:aiguard -> product:tracing, score=133)
ddtrace.debugging._signal.model -×-> ddtrace.trace  (product:debugging -> product:tracing, score=133)
ddtrace.internal.test_visibility.api -×-> ddtrace.trace  (product:ci_visibility -> product:tracing, score=133)
ddtrace.llmobs._integrations.base -×-> ddtrace.trace  (product:llmobs -> product:tracing, score=133)

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

🔄 Datadog auto-retried 2 jobs - 2 passed on retry

_{This comment will be updated automatically if new data arrives.
🔗 Commit SHA: 5703c03 | Docs | View more details | Give us feedback!}

[pr-commenter]

Benchmarks

Benchmark execution time: 2026-08-25 03:16:45

Comparing candidate commit 5703c03 in PR branch tianning.li/4-1-flask-microvm-run-hook-activation with baseline commit a0e3c42 in branch tianning.li/2-flask-web-request-starting-event.

📊 Benchmarking dashboard

Found 0 performance improvements and 11 performance regressions! Performance is the same for 603 metrics, 10 unstable metrics.

Explanation

This is an A/B test comparing a candidate commit's performance against that of a baseline commit. Performance changes are noted in the tables below as:

• 🟩 = significantly better candidate vs. baseline
• 🟥 = significantly worse candidate vs. baseline

We compute a confidence interval (CI) over the relative difference of means between metrics from the candidate and baseline commits, considering the baseline as the reference.

If the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD), the change is considered significant.

Feel free to reach out to #apm-benchmarking-platform on Slack if you have any questions.

More details about the CI and significant changes

You can imagine this CI as a range of values that is likely to contain the true difference of means between the candidate and baseline commits.

CIs of the difference of means are often centered around 0%, because often changes are not that big:

---------------------------------(------|---^--------)-------------------------------->
                              -0.6%    0%  0.3%     +1.2%
                                 |          |        |
         lower bound of the CI --'          |        |
sample mean (center of the CI) -------------'        |
         upper bound of the CI ----------------------'

As described above, a change is considered significant if the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD).

For instance, for an execution time metric, this confidence interval indicates a significantly worse performance:

----------------------------------------|---------|---(---------^---------)---------->
                                       0%        1%  1.3%      2.2%      3.1%
                                                  |   |         |         |
       significant impact threshold --------------'   |         |         |
                      lower bound of CI --------------'         |         |
       sample mean (center of the CI) --------------------------'         |
                      upper bound of CI ----------------------------------'

scenario:httppropagationextract-wsgi_valid_headers_all

• 🟥 execution_time [+435.820ns; +490.755ns] or [+8.010%; +9.020%]

scenario:httppropagationinject-ids_only

• 🟥 execution_time [+1.934µs; +2.094µs] or [+10.063%; +10.895%]

scenario:iastaspects-add_aspect

• 🟥 execution_time [+15.382µs; +18.502µs] or [+15.190%; +18.270%]

scenario:iastaspects-join_aspect

• 🟥 execution_time [+44.045µs; +49.458µs] or [+20.741%; +23.290%]

scenario:iastaspects-ljust_noaspect

• 🟥 execution_time [+58.053µs; +63.383µs] or [+20.277%; +22.139%]

scenario:iastaspects-title_aspect

• 🟥 execution_time [+66.894µs; +71.900µs] or [+25.087%; +26.964%]

scenario:iastaspectsospath-ospathbasename_aspect

• 🟥 execution_time [+143.065µs; +151.100µs] or [+35.227%; +37.205%]

scenario:iastaspectssplit-rsplit_aspect

• 🟥 execution_time [+19.545µs; +23.635µs] or [+13.527%; +16.358%]

scenario:span-start

• 🟥 execution_time [+1.424ms; +1.605ms] or [+9.390%; +10.587%]

scenario:telemetryaddmetric-1-count-metric-1-times

• 🟥 execution_time [+402.780ns; +445.184ns] or [+14.868%; +16.433%]

scenario:tracer-small

• 🟥 execution_time [+27.607µs; +30.034µs] or [+8.182%; +8.901%]

Unstable benchmarks

These benchmarks have a confidence interval too wide to call a change; treat them as noise rather than signal.

scenario:coreapiscenario-context_with_data_listeners

• unstable execution_time [-701.922ns; +786.042ns] or [-6.352%; +7.113%]

scenario:coreapiscenario-core_dispatch_1_listener

• unstable execution_time [-35.324ns; +31.047ns] or [-5.773%; +5.074%]

scenario:coreapiscenario-core_dispatch_50_listeners

• unstable execution_time [-1750.938ns; +1586.665ns] or [-10.177%; +9.222%]

scenario:coreapiscenario-core_dispatch_exception_listeners

• unstable execution_time [-1188.258ns; +1267.891ns] or [-9.230%; +9.849%]

scenario:coreapiscenario-core_dispatch_listeners

• unstable execution_time [-344.536ns; +311.594ns] or [-9.327%; +8.435%]

scenario:coreapiscenario-core_dispatch_no_args_listeners

• unstable execution_time [-278.165ns; +230.459ns] or [-9.485%; +7.858%]

scenario:coreapiscenario-core_dispatch_with_results_1_listener

• unstable execution_time [-95.601ns; +52.388ns] or [-8.308%; +4.553%]

scenario:coreapiscenario-core_dispatch_with_results_50_listeners

• unstable execution_time [-3650.380ns; +4214.846ns] or [-9.092%; +10.498%]

scenario:coreapiscenario-core_dispatch_with_results_listeners

• unstable execution_time [-759.789ns; +769.972ns] or [-9.498%; +9.625%]

scenario:packagesupdateimporteddependencies-import_many_stdlib_cached

• unstable execution_time [-63.695µs; +57.802µs] or [-9.892%; +8.977%]

[Copilot]

Pull request overview

Adds AWS Lambda MicroVM-specific runtime identity rotation triggered by Flask’s pre-request web event, so restored MicroVM instances regenerate stable identifiers (runtime ID / RC client ID) on the platform /run lifecycle hook.

Changes:

• Register a WEB_REQUEST_STARTING listener (MicroVM-only) that refreshes identity exactly once when the request matches POST /aws/lambda-microvms/runtime/v1/run.
• Add subprocess and Flask integration tests covering exact-match behavior, ordering relative to root span creation, concurrency, and no-op behavior outside MicroVMs.
• Add a release note describing stable identifier regeneration for AWS Lambda MicroVM deployments.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
ddtrace/internal/runtime/__init__.py	Adds MicroVM /run hook constants, listener registration, and the once-per-process guarded refresh logic.
tests/tracer/runtime/test_runtime_id.py	Adds unit/subprocess tests for hook matching, ordering vs. span creation, thread safety, and no-op cases.
tests/contrib/flask/test_microvm_identity_refresh.py	Updates Flask event assertions to use the real MicroVM /run hook path and verifies identity refresh via emitted events.
releasenotes/notes/aws-lambda-microvm-identity-refresh-3a672cd6bcbad16d.yaml	Documents the MicroVM-only stable identifier regeneration behavior.

---

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[litianningdatadog]

Circular import analysis

🚨 New circular imports detected 🚨

1 new circular import(s) have been introduced by this PR:

ddtrace._trace._span_pointer -> ddtrace._trace.telemetry -> ddtrace.internal.telemetry -> ddtrace.internal.telemetry.writer -> ddtrace.internal.runtime -> ddtrace.contrib._events.web_framework -> ddtrace._trace.events -> ddtrace._trace.provider -> ddtrace._trace.span -> ddtrace._trace._span_pointer

Please consider refactoring your changes in accordance to the Separation of Concerns principle.

⚠️ Existing circular imports

There are 3 circular imports that already exist on the base branch and have not been changed by this PR.

ddtrace.llmobs -> ddtrace.llmobs._evaluators -> ddtrace.llmobs._evaluators.format -> ddtrace.llmobs._experiment -> ddtrace.llmobs
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
ddtrace.appsec._asm_request_context -> ddtrace.appsec._iast._iast_request_context_base -> ddtrace.appsec._iast._iast_env -> ddtrace.appsec._iast.reporter -> ddtrace.appsec._exploit_prevention.stack_traces -> ddtrace.appsec._asm_request_context

@cit-pr-commenter-54b7da This has been fixed in upstream PR

[chatgpt-codex-connector]

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Reviewed commit: f2de1fd207

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[emmettbutler]

Converted to draft because the base is not main. Please mark as ready once the diff is ready to merge into main.