解决mininet官方镜像安装ryu后启动报错的问题

关于mininet官方镜像安装ryu后启动报错的问题

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镜像是官方镜像 mininet-2.3.0-210211-ubuntu-20.04.1-legacy-server-amd64-ovf.zip

登录后根据官方文档安装ryu，提示成功：

Successfully installed debtcollector-2.5.0 dnspython-2.2.1 eventlet-0.33.2 greenlet-2.0.1 msgpack-1.0.4 netaddr-0.8.0 oslo.config-9.0.0 oslo.i18n-5.1.0 pbr-5.11.0 repoze.lru-0.7 rfc3986-2.0.0 routes-2.5.1 ryu-4.34 stevedore-4.1.1 tinyrpc-1.1.5 webob-1.8.7

运行时报错：
ImportError: cannot import name ‘ALREADY_HANDLED’ from ‘eventlet.wsgi’ (/usr/local/lib/python3.8/dist-packages/eventlet/wsgi.py)

经查是eventlet版本过高，重新安装

sudo pip3 install  eventlet==0.30.2 -i https://pypi.douban.com/simple

ryu可以正常启动