Nova Server Group anti-affinity policy validation tool

This script checks a given Nova Server Group for any instances that fall
foul of invalid anti-affinity rules, i.e there are multiple instances
running on the same hypervisor in a Server Group where the anti-affinity
policy has been set.

Example usage:

./antiaffinitycheck.py --check c353197c-5fbb-410f-a7b3-843452a55276

Anti-affinity rules violated in Server Group: c353197c-5fbb-410f-a7b3-843452a55276
+--------------------------------------+-----------+--------------+
| Instance ID                          | Instance  | Hypervisor   |
+--------------------------------------+-----------+--------------+
| 4c38cf7f-2073-4d96-b377-d2bd29595d8a | app-db-12 | compute2.dev |
| 5c40b1e9-8b38-4978-98b2-391e53e65418 | app-db-11 | compute2.dev |
+--------------------------------------+-----------+--------------+

Change-Id: I2fee4c5eaa1aa0b511c6912f6d7cc35f736621a8

nova/antiaffinitycheck.py

@@ -0,0 +1,97 @@
+#!/usr/bin/env python
+""" Utility to check validity of anti-affinity rules """
+
+import os
+import sys
+import argparse
+from collections import defaultdict, Counter
+from keystoneclient import session
+from keystoneclient.auth.identity import v2
+from keystoneclient.v2_0 import client as ksclient
+from novaclient import client as nclient
+import prettytable
+
+def get_credentials():
+    """ Build dictionary of Keystone credentials from environment """
+    keystone_credentials = {}
+    keystone_credentials['auth_url'] = os.environ['OS_AUTH_URL']
+    keystone_credentials['username'] = os.environ['OS_USERNAME']
+    keystone_credentials['password'] = os.environ['OS_PASSWORD']
+    keystone_credentials['tenant_name'] = os.environ['OS_TENANT_NAME']
+    return keystone_credentials
+
+def get_args():
+    """ Get commandline arguments """
+    parser = argparse.ArgumentParser(description='Nova Server Group anti-affinity rule checker')
+    parser.add_argument('--check', type=str, help='Validate the specified Server Group')
+    parser.add_argument('--list', type=str, help='List instances and their hypervisors for a given Server Group')
+    return parser.parse_args()
+
+def get_server(serverid):
+    """ Return Server object """
+    return nova.servers.get(serverid)
+
+def get_group_members(server_group_id):
+    """ Return list of instance UUIDs present in a Server Group """
+    server_group = nova.server_groups.get(server_group_id)
+    if 'anti-affinity' in server_group.policies:
+        return server_group.members
+    else:
+        return False
+
+def create_table(fields):
+    """ Boilerplate for PrettyTable """
+    table = prettytable.PrettyTable(fields, caching=False)
+    table.align = 'l'
+    return table
+
+def print_group_members(server_group_id):
+    """ Print a table detailing Server Group instances and their hypervisors """
+    group_members = get_group_members(server_group_id)
+    if group_members:
+        table = create_table(['Instance ID', 'Instance', 'Hypervisor'])
+        for server in get_group_members(server_group_id):
+            instance = get_server(server)
+            hypervisor = getattr(instance, 'OS-EXT-SRV-ATTR:hypervisor_hostname'.split('.')[0])
+            table.add_row([instance.id, instance.name, hypervisor])
+        print table
+    else:
+        print "Server Group", server_group_id, "empty or does not have an anti-affinity policy set."
+
+def print_group_duplicates(server_group_id):
+    """ Evaluate whether any instances in a SG have been scheduled to the same hypervisor """
+    group_members = get_group_members(server_group_id)
+    if group_members:
+        hypervisors = []
+        instances = defaultdict(list)
+        for instance in get_group_members(server_group_id):
+            i = get_server(instance)
+            hypervisor = getattr(i, 'OS-EXT-SRV-ATTR:hypervisor_hostname')
+            instances[instance].append(i.name)
+            instances[instance].append(hypervisor)
+            hypervisors.append(hypervisor)
+        dupes = [k for k, v in Counter(hypervisors).items() if v > 1]
+        if dupes:
+            print "Anti-affinity rules violated in Server Group:", server_group_id
+            table = create_table(['Instance ID', 'Instance', 'Hypervisor'])
+            [table.add_row([instance_id, instance_name, hypervisor])
+             for instance_id, [instance_name, hypervisor] in instances.items()
+             if hypervisor in dupes]
+            print table
+        else:
+            print "No anti-affinity rules violated for Server Group:", server_group_id
+    else:
+        print "Server Group", server_group_id, "empty or does not have an anti-affinity policy set."
+
+if __name__ == '__main__':
+    credentials = get_credentials()
+    keystone = ksclient.Client(**credentials)
+    auth = v2.Password(**credentials)
+    sess = session.Session(auth=auth)
+    nova = nclient.Client(2, session=sess)
+    args = get_args()
+    group = sys.argv[2]
+    if args.check:
+        print_group_duplicates(group)
+    if args.list:
+        print_group_members(group)