Adding a host fails with the error "pip uninstall -y virtualenv failed!". What should I do?

Symptom

Adding a host on the virtualization platform fails with the following error:

stderr: ERROR: [ HOST: xx.xx.xx.xxx] ERROR: run shell command: pip uninstall -y virtualenv failed!stdout:  error: Cannot uninstall requirement virtualenv, not installed 

Solution

1. Log in to the console of the host that failed to be added and run the following command:

   # mn_ip is the VIP of the Management Node.
   pip install -i http://{mn_ip}:8080/zstack/static/pypi/simple --trusted-host {mn_ip} --ignore-installed virtualenv
   

2. Log in to the virtualization platform and add the host again. The host installation will now succeed.