docker 中 eventlet dnspython 域名解析超时

用 flask-socketio 实现了一个 socketio 的后台接口，由于 flask-socketio 依赖 eventlet，所以又安装了 eventlet。

然后发现其在 docker 内使用时，无法解析 docker compose 中配置的容器别名。

折腾了半天，最重要的收获是，尽量不要用 python eventlet 这些库，就跟玩具一样，完全浪费生命。早换 golang 早享受。

DNS Lookup timed out

redis.exceptions.ConnectionError: Error -3 connecting to redis:6379. Lookup timed out.

File "/usr/local/lib/python3.11/site-packages/eventlet/support/greendns.py", line 463, in resolve
	return _proxy.query(name, rdtype, raise_on_no_answer=raises,
File "/usr/local/lib/python3.11/site-packages/eventlet/support/greendns.py", line 419, in query
	return end()
File "/usr/local/lib/python3.11/site-packages/eventlet/support/greendns.py", line 398, in end
	raise result[1]
File "/usr/local/lib/python3.11/site-packages/dns/resolver.py", line 1076, in _compute_timeout
	raise LifetimeTimeout(timeout=duration, errors=errors)
File "/usr/local/lib/python3.11/site-packages/redis/connection.py", line 1461, in get_connection
	connection.connect()
File "/usr/local/lib/python3.11/site-packages/redis/connection.py", line 713, in connect
	raise ConnectionError(self._error_message(e))
redis.exceptions.ConnectionError: Error -3 connecting to redis:6379. Lookup timed out.

参考

• https://github.com/eventlet/eventlet/issues/619
  
• https://medium.com/@pablankley/the-eventlet-dns-bug-that-could-take-down-your-production-servers-fa873253bb40
  

找到两个类似的问题

Any progress on this? This took me many hours, too. Now I am just using dnspython==1.16.0 for a temporary workaround.

解决方案就是降级 dnspython 的版本。

查看当前环境中的 dnspython 版本

在 conda 环境内：

> pip list | grep dns
dnspython               2.6.0

降级 dnspython 版本

> pip install dnspython==1.16.0

Successfully uninstalled dnspython-2.7.0
Successfully installed dnspython-1.16.0

降级 python 版本

单纯降级 dnspython 版本，还不行。在 python 3.11 下，会报错：

AttributeError: module ‘collections’ has no attribute ‘MutableMapping’

github issue 中也提到了这个问题：

As a heads-up, it looks like supporting newer dnspython will be a necessary prerequisite to supporting Python 3.10. dnspython<2.0.0 has a reference to collections.MutableMapping, which was deprecated in favor of collections.abc.MutableMapping in py33 and removed in py310.

所以，将 docker python 镜像的版本降级为 3.9。就正常了。

确认 redis 中已成功写入数据

> docker exec -it redis /bin/sh
/data # redis-cli
127.0.0.1:6379> keys *
1) "name"

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