diff --git a/neat/globals/manager.py b/neat/globals/manager.py
index d935799..7abe777 100644
--- a/neat/globals/manager.py
+++ b/neat/globals/manager.py
@@ -276,7 +276,7 @@ def execute_underload(config, state, host):
     underloaded_host = host
     hosts_cpu_total, hosts_ram_total = state['db'].select_host_characteristics()
 
-    hosts_to_vms = vms_by_hosts(state['nova'], config['compute_hosts'])
+    hosts_to_vms = vms_by_hosts(state['nova'], state['compute_hosts'])
     vms_last_cpu = state['db'].select_last_cpu_mhz_for_vms()
 
     hosts_cpu_usage = {}
@@ -416,7 +416,7 @@ def vms_by_hosts(nova, hosts):
     """
     result = dict((host, []) for host in hosts)
     for vm in nova.servers.list():
-        result[vm_hostname(vm)].append(vm.id)
+        result[vm_hostname(vm)].append(str(vm.id))
     return result
 
 
@@ -430,7 +430,7 @@ def vm_hostname(vm):
     :return: The hostname.
      :rtype: str
     """
-    return getattr(vm, 'OS-EXT-SRV-ATTR:host')
+    return str(getattr(vm, 'OS-EXT-SRV-ATTR:host'))
 
 
 @contract
@@ -460,7 +460,7 @@ def execute_overload(config, state, vm_uuids):
      :rtype: dict(str: *)
     """
     hosts_cpu_total, hosts_ram_total = state['db'].select_host_characteristics()
-    hosts_to_vms = vms_by_hosts(state['nova'], config['compute_hosts'])
+    hosts_to_vms = vms_by_hosts(state['nova'], state['compute_hosts'])
     vms_last_cpu = state['db'].select_last_cpu_mhz_for_vms()
 
     hosts_cpu_usage = {}