Added gc_threshold overrides to sysctl.conf

When clouds have a large number of hosts, the default size of the ARP
cache is too small. The cache can overflow, which means that the
system has no way to reach some ip addresses.

Setting the threshold limits higher addresses the situation, in a
reasonably safe way (the maximum impact is 5MB or so of additional RAM
used). Docs on ARP at http://man7.org/linux/man-pages/man7/arp.7.html,
and more discussion of the issue in the bug.

Change-Id: Iaf8382ee0b42e1444cfea589bb05a687cd0c23fa
Closes-Bug: 1780348

config.yaml

@@ -379,7 +379,16 @@ options:
   # Other config
   sysctl:
     type: string
-    default:
+    default: |
+      { vm.swappiness : 1,
+        net.ipv4.neigh.default.gc_thresh1 : 128,
+        net.ipv4.neigh.default.gc_thresh2 : 28672,
+        net.ipv4.neigh.default.gc_thresh3 : 32768,
+        net.ipv6.neigh.default.gc_thresh1 : 128,
+        net.ipv6.neigh.default.gc_thresh2 : 28672,
+        net.ipv6.neigh.default.gc_thresh3 : 32768,
+        net.nf_conntrack_max : 1000000,
+        net.netfilter.nf_conntrack_max : 1000000 }
     description: |
       YAML formatted associative array of sysctl values, e.g.:
       '{ kernel.pid_max : 4194303 }'

hooks/nova_compute_hooks.py

@@ -19,13 +19,11 @@ import json
 import platform
 import sys
 import uuid
-import yaml
 import os
 import subprocess
 import grp
 import shutil
 
-
 import charmhelpers.core.unitdata as unitdata
 
 from charmhelpers.core.hookenv import (
@@ -184,10 +182,7 @@ def config_changed():
 
     sysctl_settings = config('sysctl')
     if sysctl_settings:
-        sysctl_dict = yaml.safe_load(sysctl_settings)
-        sysctl_dict['vm.swappiness'] = sysctl_dict.get('vm.swappiness', 1)
-        create_sysctl(yaml.dump(sysctl_dict),
-                      '/etc/sysctl.d/50-nova-compute.conf')
+        create_sysctl(sysctl_settings, '/etc/sysctl.d/50-nova-compute.conf')
 
     remove_libvirt_network('default')
 

unit_tests/test_nova_compute_hooks.py

@@ -215,21 +215,11 @@ class NovaComputeRelationsTests(CharmTestCase):
         self.migration_enabled.return_value = False
         self.test_config.set(
             'sysctl',
-            '{ kernel.max_pid : "1337", vm.swappiness : 10 }')
+            '{foo : bar}'
+        )
         hooks.config_changed()
         self.create_sysctl.assert_called_with(
-            "{kernel.max_pid: '1337', vm.swappiness: 10}\n",
-            '/etc/sysctl.d/50-nova-compute.conf')
-
-    @patch.object(hooks, 'compute_joined')
-    def test_config_changed_with_sysctl_swappy_default(self, compute_joined):
-        self.test_config.set(
-            'sysctl',
-            '{ kernel.max_pid : "1337" }')
-        self.migration_enabled.return_value = False
-        hooks.config_changed()
-        self.create_sysctl.assert_called_with(
-            "{kernel.max_pid: '1337', vm.swappiness: 1}\n",
+            '{foo : bar}',
             '/etc/sysctl.d/50-nova-compute.conf')
 
     @patch.object(hooks, 'compute_joined')