Configurable memcached connections limit & threads

Increasing memcached_connections may require ulimit to be raised so
that will be done if necessary.

Increasing memcached_threads is not strongly recommended but is
available if needed.

Change-Id: I4b58d59f647e6f843fc33561dea75be67c0f78c4
Closes-Bug: #1438498

playbooks/roles/memcached_server/defaults/main.yml

@@ -26,6 +26,8 @@ memcached_port: 11211
 memcached_user: memcache
 memcached_listen: "127.0.0.1"
 memcached_log: /var/log/memcached.log
+memcached_connections: 1024
+memcached_threads: 4
 
 memcached_apt_packages:
   - memcached

playbooks/roles/memcached_server/tasks/memcached_config.yml

@@ -13,7 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-- name: Drop memcached config
+- name: Apply memcached config
   template:
     src: "memcached.conf"
     dest: "/etc/memcached.conf"
@@ -23,3 +23,16 @@
   notify: Restart memcached
   tags:
     - memcached-config
+
+- name: Apply resource limits
+  template:
+    src: "memcached.j2"
+    dest: "/etc/default/memcached"
+    owner: "root"
+    group: "root"
+    mode: "0644"
+  when: >
+    memcached_connections > 1024
+  notify: Restart memcached
+  tags:
+    - memcached-config

playbooks/roles/memcached_server/templates/memcached.conf

@@ -6,3 +6,5 @@ logfile {{ memcached_log }}
 -p {{ memcached_port }}
 -u {{ memcached_user }}
 -l {{ memcached_listen }}
+-c {{ memcached_connections }}
+-t {{ memcached_threads }}

playbooks/roles/memcached_server/templates/memcached.j2

@@ -0,0 +1,6 @@
+# {{ ansible_managed }}
+# Any other value will disable memcached.
+ENABLE_MEMCACHED=yes
+
+ulimit -Hn {{ memcached_connections }}
+ulimit -n {{ memcached_connections }}