fix(rc): skip shared memory allocation in AWS Lambda

[zarirhamza]

Summary

Fixes the Unable to create shared memory. Features relying on remote configuration will not work as expected. warning that appears on every Lambda cold start since ddtrace v4.5.0.

Closes DataDog/datadog-lambda-python#785

Root Cause

The single RC subscriber refactor (v4.5.0) moved PublisherSubscriberConnector creation into RemoteConfigClient.__init__, making it eagerly constructed when the module-level remoteconfig_poller singleton is instantiated at import time. Before that refactor, connectors were created lazily per-product registration and were never created in Lambda because remote config is disabled there.

AWS Lambda does not provide /dev/shm, so the multiprocessing.Array allocation always fails with FileNotFoundError, logging the warning even though:

• DD_REMOTE_CONFIGURATION_ENABLED=false is set
• The ASM settings already disable remote config for Lambda (asm.py:284)

Both guards run after the singleton is already created — too late to prevent the allocation attempt.

Changes

• ddtrace/internal/remoteconfig/_connectors.py: Check in_aws_lambda() in PublisherSubscriberConnector.__init__ before attempting shared memory allocation. When in Lambda, skip directly to _DummySharedArray without logging a warning (this is expected behavior, not an error).
• tests/internal/remoteconfig/test_remoteconfig_connector.py: Add test verifying the connector uses _DummySharedArray when AWS_LAMBDA_FUNCTION_NAME is set.

Safety

Using _DummySharedArray in Lambda is safe because:

• .value is the only attribute accessed on the shared array — _DummySharedArray satisfies the full duck-typing contract
• connector.read() returns [] when .value is b"", which is handled gracefully by the subscriber dispatch chain (_dispatch_to_products calls periodic() on callbacks then returns early)
• The RC poller never starts in Lambda (enable() returns False), so no data is ever written to the connector
• All RC callbacks (ASM, DI, APM Tracing, Tracer Flare, Feature Flags) handle empty/no-op RC data gracefully
• This is the same _DummySharedArray already used as the FileNotFoundError fallback — we just reach it earlier and without the warning

Companion PR

Defense-in-depth change in datadog-lambda-python: DataDog/datadog-lambda-python#797 (sets DD_REMOTE_CONFIGURATION_ENABLED=false before ddtrace loads)

Test Plan

• Existing test_remoteconfig_connector.py tests pass (non-Lambda paths unchanged)
• New test_connector_uses_dummy_shared_array_in_aws_lambda test passes
• Verify no Unable to create shared memory warning in Lambda cold start logs

[brettlangdon]

needs a release note

[cit-pr-commenter-54b7da]

Codeowners resolved as

ddtrace/internal/remoteconfig/_connectors.py                            @DataDog/remote-config @DataDog/apm-core-python
releasenotes/notes/fix-lambda-shared-memory-warning-4873867125814623.yaml  @DataDog/apm-python
tests/internal/remoteconfig/test_remoteconfig_connector.py              @DataDog/remote-config @DataDog/apm-core-python

[datadog-prod-us1-6]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

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