manager: Configurable scheduler method

Added a variable in settings. It gets the value from an environment variable. The scheduler choose the method using this value.

circle/circle/settings/base.py

@@ -576,6 +576,8 @@ SESSION_COOKIE_NAME = "csessid%x" % (((getnode() // 139) ^
 MAX_NODE_RAM = get_env_variable("MAX_NODE_RAM", 1024)
 MAX_NODE_CPU_CORE = get_env_variable("MAX_NODE_CPU_CORE", 10)
 
+SCHEDULER_METHOD = get_env_variable("SCHEDULER_METHOD", 'random')
+
 # Url to download the client: (e.g. http://circlecloud.org/client/download/)
 CLIENT_DOWNLOAD_URL = get_env_variable('CLIENT_DOWNLOAD_URL', 'http://circlecloud.org/client/download/')
 

circle/manager/scheduler.py

@@ -21,6 +21,10 @@ from django.utils.translation import ugettext_noop
 
 from common.models import HumanReadableException
 
+from circle.settings.base import SCHEDULER_METHOD
+
+import random
+
 logger = getLogger(__name__)
 
 
@@ -50,9 +54,7 @@ class TraitsUnsatisfiableException(SchedulerError):
         "new virtual machine currently.")
 
 
-def select_node(instance, nodes):
-    ''' Select a node for hosting an instance based on its requirements.
-    '''
+def common_select(instance, nodes):
     # check required traits
     nodes = [n for n in nodes
              if n.schedule_enabled and n.online and
@@ -70,8 +72,32 @@ def select_node(instance, nodes):
     # sort nodes first by processor usage, then priority
     nodes.sort(key=lambda n: n.priority, reverse=True)
     nodes.sort(key=free_cpu_time, reverse=True)
+    return nodes
+
+
+def common_evenly(instance, nodes):
+    nodes = common_select(instance, nodes)
     result = nodes[0]
+    return result
 
+
+def common_random(instance, nodes):
+    nodes = common_select(instance, nodes)
+    result = random.choice(nodes)
+    return result
+
+
+def select_node(instance, nodes):
+    ''' Select a node for hosting an instance based on its requirements.
+    '''
+    if SCHEDULER_METHOD == 'evenly':
+        result = common_evenly(instance, nodes)
+    elif SCHEDULER_METHOD == 'random':
+        result = common_random(instance, nodes)
+    else:  # Default method is the random
+        result = common_random(instance, nodes)
+
+    logger.info('Scheduler method: %s selected', unicode(SCHEDULER_METHOD))
     logger.info('select_node: %s for %s', unicode(result), unicode(instance))
     return result