AWS Lambda 未显示原因 Python 3.8 中的异常堆栈跟踪

Question

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，如下所示：

[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

为什么日志中没有显示from语句的direct cause异常？

Answer 1

您提到的行为是预期的，我也看到了同样的情况。 Lambda 目前似乎不支持链式异常。 但是，为了解决这个问题，您可以添加自己的记录器来捕获异常。

例如，使用traceback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 日志如下所示：

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

Answer 2

我更喜欢的另一个解决方案是将堆栈跟踪打印到 stderr 并引发一般错误，以便程序终止。 例子：

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()

这会生成 CloudWatch output，如下所示：

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

如果有一连串异常导致Exception ，它们将被列出并由The above exception was the direct cause of the following exception: .

感谢@Paradigm 对此的启发！ 希望 AWS 很快会修复对from支持，这样我们就不必做这样的变通方法。