Introduce per-user allocation of VMs to backends

Add BACKEND_PER_USER setting, a mapping from users to backends. This setting
can by used in order to bypass the default backend allocation process, and
allocate all the new VMs of a specific user to a specific Backend.

snf-cyclades-app/synnefo/api/servers.py

@@ -257,7 +257,7 @@ def create_server(request):
             raise faults.OverLimit("Server count limit exceeded for your account.")
 
         backend_allocator = BackendAllocator()
-        backend = backend_allocator.allocate(flavor)
+        backend = backend_allocator.allocate(request.user_uniq, flavor)
 
         if backend is None:
             log.error("No available backends for VM with flavor %s", flavor)

snf-cyclades-app/synnefo/app_settings/default/api.py

@@ -98,6 +98,10 @@ APPEND_SLASH = False
 #
 IGNORE_FLAVOR_DISK_SIZES = False
 
+# Fixed mapping of user VMs to a specific backend.
+# e.g. BACKEND_PER_USER = {'example@okeanos.grnet.gr': 2}
+BACKEND_PER_USER = {}
+
 # Quota
 #
 # Maximum number of VMs a user is allowed to have.

snf-cyclades-app/synnefo/logic/backend_allocator.py

@@ -31,7 +31,8 @@ import logging
 import datetime
 from django.utils import importlib
 
-from synnefo import settings
+from synnefo.settings import (BACKEND_ALLOCATOR_MODULE, BACKEND_REFRESH_MIN,
+                              BACKEND_PER_USER)
 from synnefo.db.models import Backend
 from synnefo.logic.backend import update_resources
 from synnefo.api.util import backend_public_networks
@@ -45,9 +46,9 @@ class BackendAllocator():
     """
     def __init__(self):
         self.strategy_mod =\
-            importlib.import_module(settings.BACKEND_ALLOCATOR_MODULE)
+            importlib.import_module(BACKEND_ALLOCATOR_MODULE)
 
-    def allocate(self, flavor):
+    def allocate(self, userid, flavor):
         """Allocate a vm of the specified flavor to a backend.
 
         Warning!!: An explicit commit is required after calling this function,
@@ -55,6 +56,12 @@ class BackendAllocator():
         function.
 
         """
+
+        backend = None
+        backend = get_backend_for_user(userid)
+        if backend:
+            return backend
+
         # Get the size of the vm
         disk = flavor_disk(flavor)
         ram = flavor.ram
@@ -138,9 +145,30 @@ def refresh_backends_stats(backends):
     """
 
     now = datetime.datetime.now()
-    delta = datetime.timedelta(minutes=settings.BACKEND_REFRESH_MIN)
+    delta = datetime.timedelta(minutes=BACKEND_REFRESH_MIN)
     for b in backends:
         if now > b.updated + delta:
             log.debug("Updating resources of backend %r. Last Updated %r",
                       b, b.updated)
             update_resources(b)
+
+
+def get_backend_for_user(userid):
+    """Find fixed Backend for user based on BACKEND_PER_USER setting."""
+
+    backend = BACKEND_PER_USER.get(userid)
+
+    if not backend:
+        return None
+
+    try:
+        try:
+            backend_id = int(backend)
+            return Backend.objects.get(id=backend_id)
+        except ValueError:
+            pass
+
+        backend_name = str(backend)
+        return Backend.objects.get(clustername=backend_name)
+    except Backend.DoesNotExist:
+        log.error("Invalid backend %s for user %s", backend, userid)