conntrack: set sane sysctl defaults

swift-storage is often deployed alongside nova-compute where it
inherits some sane defaults for sysctl values, specifically around
conntrack configuration.

If its deployed standalone it does not recieve the same tuning,
but its very much applicable as access between swift-storage nodes
for rsync traffic is firewall limited so makes a high demand
on conntrack on the server.

Lift and shift the defaults from the nova-compute charm.

Change-Id: Iedd27a51ff93fd1670a418e1434c94875fe21643
Closes-Bug: 1879121

config.yaml

@@ -191,7 +191,16 @@ options:
       to run. Supported modules currently include os, ssh, apache and mysql.
   sysctl:
     type: string
-    default:
+    default: |
+      { 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_buckets : 204800,
+        net.netfilter.nf_conntrack_max : 1000000 }
     description: |
       YAML formatted associative array of sysctl values, e.g.:
       '{ kernel.pid_max : 4194303 }'

unit_tests/test_swift_storage_relations.py

@@ -67,6 +67,7 @@ TO_PATCH = [
     'setup_ufw',
     'revoke_access',
     'kv',
+    'create_sysctl',
 ]