I installed OpenStack on an ec2 instance running Ubuntu 14.04 LTS via devstack. When I login into the dashboard I get an error "Error: Unable to retrieve usage information" When I installed it and logged in for the first time, everything was working fine. But after I stopped my ec2 instance and restarted, I am facing this problem. What might be causing this error? I used the stable juno version of devstack. And the AMI for my ec2 instance is Ubuntu Server 14.04 LTS (HVM), SSD Volume Type. Does restarting the instance might have caused some problem?
cd to devstack and execute ./rejoin-stack That solved it. I was trying to reboot nova and other services individually. But since the installation was done using devstack, you need to run the ./rejoin-stack script.
In addition to [akshay1188] answer, you can re-stack your system. Sometimes, rejoin-stack does not work as expected. In that case, you can unstack (unstack.sh) it and stack (stack.sh) again. *This may take much time.
Another observation of mine says this can be an issue with IP address of the system. Try to keep IP address same after reboot.
来源：https://stackoverflow.com/questions/29328151/openstack-dashboard-gives-error-error-unable-to-retrieve-usage-information