Bug: log sampling is not working in v2

[theburningmonk]

Expected Behavior

When POWERTOOLS_LOG_SAMPLE_RATE is set to 0.1 and every invocation includes a call to logger.refreshSampleRateCalculation() to recalculate the sampling rate, the debug logs should be recorded for only 10% of invocations.

Current Behavior

The sampling decision is made at cold start, and then all invocations afterwards will either log all debug logs or none at all. The refreshSampleRateCalculation() method is not giving the correct behaviour.

Code snippet

This line is included at the start of a handler function:

logger.refreshSampleRateCalculation()

The POWERTOOLS_LOG_LEVEL env var is set to ERROR.
The POWERTOOLS_LOGGER_SAMPLE_RATE env var is set to 0.1

Steps to Reproduce

Create a function with:

• POWERTOOLS_LOGGER_SAMPLE_RATE env var set to 0.1
• POWERTOOLS_LOG_LEVEL env var set to ERROR
• include a call to logger.refreshSampleRateCalculation() at the start of the handler
• include a few debug logs
  Invoke the function multiple times to see sampling decision is taken once, at cold start, but then never changed on subsequent invocations on the same worker

Possible Solution

No response

Powertools for AWS Lambda (TypeScript) version

latest

AWS Lambda function runtime

20.x

Packaging format used

npm

Execution logs

No response

[boring-cyborg]

Thanks for opening your first issue here! We'll come back to you as soon as we can.
In the meantime, check out the #typescript channel on our Powertools for AWS Lambda Discord: Invite link

[dreamorosi]

Hi @theburningmonk, thank you for opening the issue.

As I mentioned in the thread we exchanged I think the report is valid and we have a bug.

I am currently investigating and I will share more info once I have a definitive answer.

[dreamorosi]

Hi Yan, just wanted to let you know that I identified the bug and that I have already opened a PR with a proposed fix.

The root cause of the bug was the one that I hinted at yesterday during our exchange on Twitter. Basically we were not restoring the log level to the original one after having sampled a specific invocation.

Once the PR is merged it will be included in the next release.

In the meanwhile, if you want to continue upgrading before the release, a workaround like this would work:

import { Logger } from '@aws-lambda-powertools/logger';

const logger = new Logger({ sampleRateValue: 0.1, logLevel: 'ERROR' });

export const handler = async () => {
+ logger.setLogLevel('ERROR'); // TODO: remove after next release
  logger.refreshSampleRateCalculation();
  
  logger.debug('This is a debug message - should not appear every time');

  return {
    statusCode: 200,
    body: JSON.stringify("Hello, World!"),
  };
};

[github-actions]

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[github-actions]

This is now released under v2.3.0 version!