问题描述

在Azure中创建Function App（函数应用）, 用以运行Python代码（Python Version 3.7)。 通过VS Code创建一个HttpTrigger的Function，其中使用到了 psycopg2 模块，以便连接  Azure Database for PostgreSQL 数据库

当通过VS Code发布到Azure后，请求 Function URL 出错。通过高级工具(Kudu：https://<xxxxxxxx>.scm.chinacloudsites.cn/)登录到Logfiles中查看到错误消息为：

错误消息显示：ModuleNotFoundError: No module named 'psycopg2'. Troubleshooting Guide: https://aka.ms/functions-modulenotfound

完整的错误消息为：

2021-11-24T01:55:27.767 [Information] Executing 'Functions.HttpTrigger1' (Reason='This function was programmatically called via the host APIs.', Id=fb46530a-60db-4d44-b705-e81f805c9743)
2021-11-24T01:55:28.640 [Information] Worker process started and initialized.
2021-11-24T01:55:28.762 [Error] Executed 'Functions.HttpTrigger1' (Failed, Id=fb46530a-60db-4d44-b705-e81f805c9743, Duration=1095ms)
Result: Failure
Exception: ModuleNotFoundError: No module named 'psycopg2'. Troubleshooting Guide: https://aka.ms/functions-modulenotfound
Stack:   File "/azure-functions-host/workers/python/3.8/LINUX/X64/azure_functions_worker/dispatcher.py", line 305, in _handle__function_load_request
func = loader.load_function(
File "/azure-functions-host/workers/python/3.8/LINUX/X64/azure_functions_worker/utils/wrappers.py", line 42, in call
raise extend_exception_message(e, message)
File "/azure-functions-host/workers/python/3.8/LINUX/X64/azure_functions_worker/utils/wrappers.py", line 40, in call
return func(*args, **kwargs)
File "/azure-functions-host/workers/python/3.8/LINUX/X64/azure_functions_worker/loader.py", line 85, in load_function
mod = importlib.import_module(fullmodname)
File "/usr/local/lib/python3.8/importlib/__init__.py", line 127, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
File "/home/site/wwwroot/HttpTrigger1/__init__.py", line 2, in <module>
import psycopg2

问题分析

当遇见模块无法安装的时候，可以参考 TroubleShooting Guide (https://aka.ms/functions-modulenotfound)  进行逐步排查，还是非常有帮助的。

但是当前问题，并不是没有尝试安装psycopg2这个模块，而是虽然在Function的 requirements.txt 文件中已经添加了psycopg2，但是在安装的过程中出错。为了更明确的知道错误的消息，直接SSH连接到Function App所运行的Linux实例。通过 python -m pip install psycopg2 查看错误信息：

错误文本：

root@1ac8c89f91a9:~#  python -m pip install psycopg2
Collecting psycopg2
Downloading psycopg2-2.9.2.tar.gz (380 kB)
|████████████████████████████████| 380 kB 274 kB/s
ERROR: Command errored out with exit status 1:
command: /usr/local/bin/python -c 'import io, os, sys, setuptools, tokenize; sys.argv[0] = '"'"'/tmp/pip-install-zvgqohj2/psycopg2_46223be3606547c5bbdd49a650506
7d8/setup.py'"'"'; __file__='"'"'/tmp/pip-install-zvgqohj2/psycopg2_46223be3606547c5bbdd49a6505067d8/setup.py'"'"';f = getattr(tokenize, '"'"'open'"'"', open)(__file
__) if os.path.exists(__file__) else io.StringIO('"'"'from setuptools import setup; setup()'"'"');code = f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exe
c(compile(code, __file__, '"'"'exec'"'"'))' egg_info --egg-base /tmp/pip-pip-egg-info-4y8snj3a
cwd: /tmp/pip-install-zvgqohj2/psycopg2_46223be3606547c5bbdd49a6505067d8/
Complete output (23 lines):
running egg_info
creating /tmp/pip-pip-egg-info-4y8snj3a/psycopg2.egg-info
writing /tmp/pip-pip-egg-info-4y8snj3a/psycopg2.egg-info/PKG-INFO
writing dependency_links to /tmp/pip-pip-egg-info-4y8snj3a/psycopg2.egg-info/dependency_links.txt
writing top-level names to /tmp/pip-pip-egg-info-4y8snj3a/psycopg2.egg-info/top_level.txt
writing manifest file '/tmp/pip-pip-egg-info-4y8snj3a/psycopg2.egg-info/SOURCES.txt'

Error: pg_config executable not found.

pg_config is required to build psycopg2 from source.  Please add the directory
containing pg_config to the $PATH or specify the full executable path with the
option:

python setup.py build_ext --pg-config /path/to/pg_config build ...

or with the pg_config option in 'setup.cfg'.

If you prefer to avoid building psycopg2 from source, please install the PyPI
'psycopg2-binary' package instead.

For further information please check the 'doc/src/install.rst' file (also at
<https://www.psycopg.org/docs/install.html>).

----------------------------------------
WARNING: Discarding https://files.pythonhosted.org/packages/33/ed/79434011d773e5ea4c51262f6ebfb86680c2908d7677f31ebccd5aa9f1b3/psycopg2-2.9.2.tar.gz#sha256=a84da9fa8
91848e0270e8e04dcca073bc9046441eeb47069f5c0e36783debbea (from https://pypi.org/simple/psycopg2/) (requires-python:>=3.6). Command errored out with exit status 1: pyt
hon setup.py egg_info Check the logs for full command output.

真正的错误就是 pg_config 是必须的，但是Linux实例上并没有配置。而解决办法就是使用 psycopg2-binary 包代替，接着使用  python -m pip install psycopg2-binary 来测试是否可以安装成功。

验证成功！

所以为了能在 Python Function 中使用 psycopg2 模块，需要在 requirements.txt 文件中，使用 psycopg2-binary 代替 psycopg2。 其他的(如代码中的 import psycopg2)则无需修改。

参考资料

在 Azure 中使用 Visual Studio Code 创建 Python 函数 ： https://docs.azure.cn/zh-cn/azure-functions/create-first-function-vs-code-python

Use Python to connect and query data in Azure Database for PostgreSQL - Single Server ： https://docs.microsoft.com/en-us/azure/postgresql/connect-python#prerequisites

Using psycopg2 in Azure Functions : https://iotespresso.com/using-psycopg2-in-azure-functions/

psycopg2 is not a standalone package. It is built using libpq-dev package, during installation. Now, psycopg2 depends on the host OS to find this library. And Azure Functions don’t have libpq, as the error above clearly indicates.

You may be wondering that we can perhaps simply add libpq-dev to requirements.txt. But that doesn’t work. You will get the error:

Thus, the required solution is to use a package of psycopg2 that doesn’t require libpq. psycopg2-binary is exactly that. I hope this provided a satisfactory explanation.

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