Only update apt cache if necessary

Workarounding the upstream ansible apt module bug

documented here:

https://github.com/ansible/ansible-modules-core/pull/1517

For the next versions of ansible we'll be using, we should

check if the apt bug is fixed. When it's fixed, we could

abandon this change and use the standard apt module

with correct cache handling.

Change-Id: I900ea91ca60973fc72910d649ec1f994373fbe5f

defaults/main.yml

@@ -13,6 +13,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+## APT Cache Options
+cache_timeout: 600
+
 # Defines that the role will be deployed on a host machine
 is_metal: true
 

tasks/memcached_install.yml

@@ -13,14 +13,20 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-- name: Update apt sources
+#TODO(evrardjp): Replace the next 2 tasks by a standard apt with cache
+#when https://github.com/ansible/ansible-modules-core/pull/1517 is merged
+#in 1.9.x or we move to 2.0 (if tested working)
+- name: Check apt last update file
+  stat:
+    path: /var/cache/apt
+  register: apt_cache_stat
+  tags:
+    - memcached-apt-packages
+
+- name: Update apt if needed
   apt:
     update_cache: yes
-    cache_valid_time: 600
-  register: apt_update
-  until: apt_update|success
-  retries: 5
-  delay: 2
+  when: "ansible_date_time.epoch|float - apt_cache_stat.stat.mtime > {{cache_timeout}}"
   tags:
     - memcached-apt-packages