Increase default metadata_workers, backlog to 4096

While deployment tools might want to change the number of workers
to match the number of cores (Or some fraction of it), any default
other than 1 should be outright better.

Inspired from 19:34:
https://www.youtube.com/watch?v=AF9r_VQrcJ0

DocImpact
Closes-Bug: #1323005
Change-Id: Ie90000183ae67ff391a23ca3213fd23aef5f4dc5

etc/metadata_agent.ini

@@ -45,11 +45,12 @@ admin_password = %SERVICE_PASSWORD%
 # Location of Metadata Proxy UNIX domain socket
 # metadata_proxy_socket = $state_path/metadata_proxy
 
-# Number of separate worker processes for metadata server
-# metadata_workers = 0
+# Number of separate worker processes for metadata server. Defaults to
+# half the number of CPU cores
+# metadata_workers =
 
 # Number of backlog requests to configure the metadata server socket with
-# metadata_backlog = 128
+# metadata_backlog = 4096
 
 # URL to connect to the cache backend.
 # default_ttl=0 parameter will cause cache entries to never expire.

neutron/agent/metadata/agent.py

@@ -306,11 +306,11 @@ class UnixDomainMetadataProxy(object):
                    default='$state_path/metadata_proxy',
                    help=_('Location for Metadata Proxy UNIX domain socket')),
         cfg.IntOpt('metadata_workers',
-                   default=0,
+                   default=utils.cpu_count() // 2,
                    help=_('Number of separate worker processes for metadata '
                           'server')),
         cfg.IntOpt('metadata_backlog',
-                   default=128,
+                   default=4096,
                    help=_('Number of backlog requests to configure the '
                           'metadata server socket with'))
     ]

neutron/common/utils.py

@@ -22,6 +22,7 @@ import datetime
 import functools
 import hashlib
 import logging as std_logging
+import multiprocessing
 import os
 import random
 import signal
@@ -291,3 +292,10 @@ def get_dhcp_agent_device_id(network_id, host):
     local_hostname = host.split('.')[0]
     host_uuid = uuid.uuid5(uuid.NAMESPACE_DNS, str(local_hostname))
     return 'dhcp%s-%s' % (host_uuid, network_id)
+
+
+def cpu_count():
+    try:
+        return multiprocessing.cpu_count()
+    except NotImplementedError:
+        return 1