patch_all() can patch modules multiple times, causing RecursionErrors

[nathanreynolds-kcom]

We hit an issue where patch_all() was used in a Lambda function - after the 1000th call we saw a RecursionError when calling requests.get().

Example:

from aws_xray_sdk.core import patch_all
import requests
import sys

def lambda_handler(event, _context):
    for i in range(sys.getrecursionlimit()):
        patch_all()
    requests.get('https://google.com') # Triggers RecursionError

We should have called patch_all() outside of the function, but this still feels like a gotcha.

core.patcher._patch has this code:

def _patch(module_to_patch):
    # [...]
    if module_to_patch in _PATCHED_MODULES:
        log.debug('%s already patched', module_to_patch)

So it recognises the multiple patch, but repatches anyway.

Should _patch return early if it recognises the patch is already in place?

[haotianw465]

Thank you for reporting the issue. This is a bug and we will work on a fix soon. Just want to clarify, does calling patch_all() outside the handler workaround the problem for you? When you say the 1000th call does it mean you got this error in your 1000th lambda function execution?

[nathanreynolds-kcom]

Haven't tested extensively yet, hopeful having a single patch_all at initialisation should solve it - will let you know if that's not the case.

And yep, we saw it after a single instance of the Lamba function had been called 1000 times. This was under load so we were at max concurrency and all instances were active.

[haotianw465]

The issue is fixed in 2.2.0 https://pypi.org/project/aws-xray-sdk/. Closing.