AWS Lambda在Python 3.8中不显示原因 异常堆栈跟踪

Posted 2021-05-07

我使用运行时Python 3.8将以下代码部署到AWS Lambda。

try:
    raise Exception('my exception')
except Exception as e:
    raise ValueError('my exception 2') from e

在 CloudWatch 中，我希望看到这样的异常链。

Traceback (most recent call last):
  File "/var/task/handler.py", line 2, in <module>
    raise Exception('my exception')
Exception: my exception

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/var/task/handler.py", line 4, in <module>
    raise ValueError('my exception 2') from e
ValueError: my exception 2

相反，我只看到CloudWatch中报告的第一个异常是这样的。

[ERROR] ValueError: my exception 2
Traceback (most recent call last):
  File "/var/task/handler.py", line 21, in pevm_import_budget_file
    raise ValueError('my exception 2') from e

为什么不是 direct cause 例外 from 语句显示在日志中？

答案

您提到的行为是意料之中的，我也看到了同样的情况。似乎 Lambda 目前不支持链式异常。不过，要解决这个问题，您可以添加自己的日志记录器来捕获异常。

例如，使用 回溯 来检索异常堆栈。

import traceback

def lambda_handler(event, context):
    try:
        try:
            raise Exception('my exception')
        except Exception as e1:
            raise ValueError('my exception 2')
    except Exception as e2:
        traceback.print_exception(type(e2), value=e2, tb=e2.__traceback__)

    return {}

CloudWatch的日志是这样的：

Traceback (most recent call last):
  File "/var/task/lambda_function.py", line 6, in lambda_handler
    raise Exception('my exception')
Exception: my exception

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/var/task/lambda_function.py", line 8, in lambda_handler
    raise ValueError('my exception 2')
ValueError: my exception 2

另一答案

我喜欢的另一个解决方案是将堆栈跟踪打印到stderr，并引发一个通用错误，使程序终止。例子：这将产生 CloudWatch 的输出，如以下所示。

import logging, traceback, sys

class ProgramError(Exception):
    def __init__(self, msg='There should be more of exception traceback above.', **kwargs):
        super(ProgramError, self).__init__(msg, **kwargs)


def log_exception():
    exc_type, exc_value, exc_traceback = sys.exc_info()
    logging.error(''.join(traceback.format_exception(exc_type, exc_value, exc_traceback)))


try:
    raise Exception('my exception')
except Exception as e:
    log_exception()
    raise ProgramError()

这将产生CloudWatch这样的输出

2020-06-02T06:08:57.340000+00:00 2020/06/02/[$LATEST]df0f5bb977b443f9889a809f0d1affa4 START RequestId: e609f118-75d9-4cc7-81fe-44036d492814 Version: $LATEST
2020-06-02T06:08:57.341000+00:00 2020/06/02/[$LATEST]df0f5bb977b443f9889a809f0d1affa4 [ERROR]   2020-06-02T06:08:57.341Z    e609f118-75d9-4cc7-81fe-44036d492814    Traceback (most recent call last):
  File "/var/task/handler.py", line 35, in testfile
    raise Exception('my exception')
Exception: my exception
2020-06-02T06:08:57.342000+00:00 2020/06/02/[$LATEST]df0f5bb977b443f9889a809f0d1affa4 [ERROR] ProgramError: There should be more of exception traceback above.
Traceback (most recent call last):
  File "/var/task/handler.py", line 38, in testfile
    raise ProgramError()
2020-06-02T06:08:57.343000+00:00 2020/06/02/[$LATEST]df0f5bb977b443f9889a809f0d1affa4 END RequestId: e609f118-75d9-4cc7-81fe-44036d492814
2020-06-02T06:08:57.343000+00:00 2020/06/02/[$LATEST]df0f5bb977b443f9889a809f0d1affa4 REPORT RequestId: e609f118-75d9-4cc7-81fe-44036d492814    Duration: 2.71 ms   Billed Duration: 100 ms Memory Size: 256 MB Max Memory Used: 95 MB  Init Duration: 1297.82 ms

如果有一连串的异常导致了 Exception它们将被列出，并以 The above exception was the direct cause of the following exception:.

感谢@Paradigm给我的灵感! 希望AWS能修复对 from 这样我们就不用再做这样的变通工作了。