Python layer 0.21.0 + Python 3.14: SystemError importing google._upb._message via google.cloud.pubsub_v1 (Serverless zipped deps)

[jairhenrique]

Describe the bug

After upgrading the OpenTelemetry Python Lambda layer to 0.21.0, our function fails at cold start while otel_wrapper.py imports the handler.

The crash happens when the handler imports google.cloud.pubsub_v1. That import chain loads proto-plus, which then imports the protobuf C extension google._upb._message and raises:

  SystemError: <built-in function __import__> returned a result with an exception set

This started only after the layer bump to 0.21.0 (same function code and same Serverless packaging). Pinning the function dependency protobuf==7.35.1 restores a successful import (newer protobuf 7.36.x pulled by google-cloud-pubsub failed on this runtime).

This looks like a protobuf / google._upb native-extension conflict on Python 3.14: two copies of protobuf on sys.path (layer under /opt/python vs. Serverless zipped deps under /tmp/sls-py-req), and/or an ABI issue of protobuf 7.36.x with CPython 3.14 on Linux aarch64 when the layer wrapper is in the import path.

Steps to reproduce

1. AWS Lambda, Python 3.14, architecture arm64.
2. Attach ADOT / OTel Python layer opentelemetry-python-0_21_0 (ARN pattern arn:aws:lambda:<region>:184161586896:layer:opentelemetry-python-0_21_0:1). Handler is wrapped by /opt/python/otel_wrapper.py.
3. Package application dependencies with Serverless Framework v4 using serverless-python-requirements:
   • pythonRequirements.zip: true (deps extracted at runtime to /tmp/sls-py-req)
   • dockerizePip: non-linux
   • useUv: true
4. Function depends on google-cloud-pubsub (we use 2.39.2) and imports from google.cloud import pubsub_v1 at module load (not inside the handler).
5. Do not pin protobuf (let Pub/Sub pull the latest, currently 7.36.x).
6. Invoke the function (cold start).

What did you expect to see?

The wrapper should import the handler and Pub/Sub (google.cloud.pubsub_v1 / proto / protobuf) without crashing, as with the previous Python layer (pre-0.21.0).

What did you see instead?

Cold-start failure before the handler runs. CloudWatch:

  {
    "errorMessage": "<built-in function __import__> returned a result with an exception set",
    "errorType": "SystemError",
    "stackTrace": [
      "  File \"/var/lang/lib/python3.14/importlib/__init__.py\", line 88, in import_module\n    return _bootstrap._gcd_import(name[level:], package, level)\n",
      "  File \"/opt/python/otel_wrapper.py\", line 61, in <module>\n    handler_module = import_module(modified_mod_name)\n",
      "  File \"/var/task/src/functions/send_data_gcp_function.py\", line 5, in <module>\n    from src.domain.use_cases.send_data_gcp.send_data_gcp_use_case import SendDataGCPUseCase\n",
      "  File \"/var/task/src/domain/use_cases/send_data_gcp/send_data_gcp_use_case.py\", line 12, in <module>\n    from src.services.message.pubsub.producer import GCPProducer\n",
      "  File \"/var/task/src/services/message/pubsub/producer.py\", line 3, in <module>\n    from google.cloud import pubsub_v1\n",
      "  File \"/tmp/sls-py-req/google/cloud/pubsub_v1/__init__.py\", line 17, in <module>\n    from google.cloud.pubsub_v1 import publisher, subscriber, types\n",
      "  File \"/tmp/sls-py-req/google/cloud/pubsub_v1/publisher/client.py\", line 30, in <module>\n    from google.cloud.pubsub_v1 import types\n",
      "  File \"/tmp/sls-py-req/google/cloud/pubsub_v1/types.py\", line 24, in <module>\n    import proto\n",
      "  File \"/tmp/sls-py-req/proto/marshal/compat.py\", line 27, in <module>\n    from google._upb import _message as _message_upb\n"
    ]
  }

What version of collector/language SDK version did you use?

• Python layer: layer-python/0.21.0 (opentelemetry-python-0_21_0:1)
• Language SDK bundled in that layer: OpenTelemetry Python 1.44.0 / 0.65b0 (layer-python/0.21.0)
• Collector layer: not required to reproduce (failure is in the Python wrapper import path). We can attach collector version if useful.

What language layer did you use?

• Python (opentelemetry-python-0_21_0), AWS Lambda python3.14, arm64.

Additional context
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