python 3.9 runtime update gives Runtime.Unknown in INIT phase

Question

A group of lambda functions using the python 3.9 Runtime were updated yesterday (from v96 to v101)  which caused the following errors.

```
INIT_START Runtime Version: python:3.9.v101	
Runtime Version ARN: arn:aws:lambda:eu-west-2::runtime:*********************************************************

Phase: init	Status: error	Error Type: Runtime.Unknown
```

We have since reverted back to our previous runtime arn
INIT_START Runtime Version: python:3.9.v96	Runtime Version ARN: arn:aws:lambda:eu-west-2::runtime:abe2e7e38f4*************************521cf4a70********b95855aa019258

Can you help with suggesting how we move forward.
We have run our function code with the latest python release (3.9.23) locally and cannot see any dependency issues

It would be great to also get clarity on what exactly is in the v101 Runtime, and if the changelog is publicly available for review.

Thanks,
Alan

re:Post Agent · Answer

When facing a "Runtime.Unknown" error after a Lambda runtime update, this indicates a compatibility issue between your function and the new runtime version.

To move forward, you have a few options:

1. Investigate the specific error: The "Runtime.Unknown" error is quite generic. Check the complete CloudWatch logs for more detailed error messages that might help identify the root cause.

2. Test incrementally: Since you've already reverted to v96 successfully, you could try updating to intermediate versions between v96 and v101 to identify which specific version introduces the issue.

3. Review dependencies: Although you've tested with Python 3.9.23 locally, Lambda's runtime environment might differ. Check if you're using any libraries with native extensions (like psycopg2) that might need to be recompiled or updated for the new runtime.

4. Update your runtime management configuration: Consider changing from Auto mode to Function update mode, which would allow you to control when runtime updates are applied to your function.

Regarding the runtime version changelog, AWS Lambda doesn't typically publish detailed changelogs for specific runtime version updates. The runtime versions include security patches, bug fixes, and performance improvements, but detailed information about what's in v101 specifically isn't publicly available.

If you need to continue using the latest runtime version, you might need to update your function code or dependencies to be compatible with the changes in v101. Alternatively, you can continue using v96 in Manual mode until you're ready to update, though it's generally recommended to use the latest runtime version for security and performance benefits.  
**Sources**  
[Troubleshoot Lambda function runtime version errors | AWS re:Post](https://repost.aws/knowledge-center/lambda-runtime-version-error)  
[Learn the differences between Lambda runtime version and runtime identifier | AWS re:Post](https://repost.aws/knowledge-center/lambda-runtime-version-identifier)  
[Identifying Lambda runtime version changes - AWS Lambda](https://docs.aws.amazon.com/lambda/latest/dg/runtime-management-identify.html)  
[Rolling back a Lambda runtime version - AWS Lambda](https://docs.aws.amazon.com/lambda/latest/dg/runtime-management-rollback.html)

python 3.9 runtime update gives Runtime.Unknown in INIT phase

Add your answer

Relevant content