When you attach a nova volume to a VM, you will see the error with stack trace in /var/log/nova/nova-volume.log. The JSON serializable issue is caused by an RPC response timeout.

Make sure your iptables allow port 3260 communication on the ISC controller. Run this command: # iptables -I INPUT <Last Rule No> -p tcp --dport 3260 -j ACCEPT If the port communication is properly configured, you can try running this command. # service iptables stop This service does not exist on Debian or Ubuntu. If you continue to get the RPC response time out, your ISC controller and KVM host might be incompatible.