a

config.py

@@ -19,6 +19,7 @@ host_prefix = config("HOST_PREFIX")
 request_prefix = config("REQUEST_PREFIX")
 
 etcd_client = Etcd3Wrapper(host=config("ETCD_URL"))
+
 vm_pool = VmPool(etcd_client, vm_prefix)
 host_pool = HostPool(etcd_client, host_prefix)
 request_pool = RequestPool(etcd_client, request_prefix)

helper.py

@@ -28,6 +28,11 @@ def remaining_resources(host_specs, vms_specs):
     return remaining
 
 
+class NoSuitableHostFound(Exception):
+    """Raise this exception when no host found
+       that can host a VM"""
+
+
 def get_suitable_host(vm_specs, hosts=None):
     if hosts is None:
         hosts = host_pool.by_status(HostStatus.alive)
@@ -62,7 +67,7 @@ def get_suitable_host(vm_specs, hosts=None):
         ):
             return host.key
 
-    return None
+    raise NoSuitableHostFound
 
 
 def dead_host_detection():
@@ -92,23 +97,13 @@ def dead_host_mitigation(dead_hosts_keys):
 
 
 def assign_host(vm):
-    host_name = get_suitable_host(vm.specs)
-    if host_name:
-        # if vm.status == VMStatus.requested_new:
-        #     vm.status = VMStatus.scheduled_deploy
-        #
-        # if vm.status == VMStatus.killed:
-        #     vm.status = VMStatus.requested_start
+    vm.hostname = get_suitable_host(vm.specs)
+    vm_pool.put(vm)
 
-        vm.hostname = host_name
-        vm_pool.put(vm)
+    r = RequestEntry.from_scratch(type=RequestType.StartVM,
+                                  uuid=vm.uuid,
+                                  hostname=vm.hostname)
+    request_pool.put(r)
 
-        r = RequestEntry.from_scratch(type=RequestType.StartVM,
-                                      uuid=vm.uuid,
-                                      hostname=vm.hostname)
-        request_pool.put(r)
-
-        vm.log.append("VM scheduled for starting")
-
-        return host_name
-    return None
+    vm.log.append("VM scheduled for starting")
+    return vm.hostname

main.py

@@ -10,7 +10,7 @@ from config import etcd_client as client
 from config import (host_pool, request_pool, vm_pool, request_prefix)
 from ucloud_common.request import RequestEntry, RequestType
 from helper import (get_suitable_host, dead_host_mitigation, dead_host_detection,
-                    assign_host)
+                    assign_host, NoSuitableHostFound)
 
 pending_vms = []
 
@@ -51,29 +51,32 @@ def main():
                                                   hostname=pending_vm_entry.hostname)
                     request_pool.put(r)
 
-                logging.debug(f"Remaining Pending: {pending_vms}")
-
             elif request_entry.type == RequestType.ScheduleVM:
                 vm_entry = vm_pool.get(request_entry.uuid)
                 client.client.delete(request_entry.key)  # consume Request
 
-                # If Request is about a VM which is labelled as "migration"
+                # If the Request is about a VM which is labelled as "migration"
                 # and has a destination
                 if hasattr(request_entry, "migration") and request_entry.migration \
                         and hasattr(request_entry, "destination") and request_entry.destination:
-                    host = get_suitable_host(vm_entry.specs, [host_pool.get(request_entry.destination)])
-                    if host:
+                    try:
+                        get_suitable_host(vm_entry.specs, [host_pool.get(request_entry.destination)])
+                    except NoSuitableHostFound:
+                        logging.info("Requested destination host doesn't have enough capacity"
+                                     f"to hold {vm_entry.uuid}")
+                    else:
                         r = RequestEntry.from_scratch(type=RequestType.InitVMMigration,
                                                       uuid=request_entry.uuid,
                                                       destination=request_entry.destination)
                         request_pool.put(r)
-                    else:
-                        logging.info("Requested destination host doesn't have enough capacity"
-                                     f"to hold {vm_entry.uuid}")
+
+                # If the Request is about a VM that just want to get started/created
                 else:
                     # assign_host only returns None when we couldn't be able to assign
                     # a host to a VM because of resource constraints
-                    if assign_host(vm_entry) is None:
+                    try:
+                        assign_host(vm_entry)
+                    except NoSuitableHostFound:
                         vm_entry.log.append("Can't schedule VM. No Resource Left.")
                         vm_pool.put(vm_entry)