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: I00d6d0704e77bc3f8f19fb36933ac518b3372e8d

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
+
 # rsyslog_server_apt_repos:
 #   - { repo: "ppa:adiscon/v8-stable", state: "present" }
 

tasks/rsyslog_server_install.yml

@@ -26,14 +26,22 @@
   tags:
     - rsyslog-apt-repositories
 
-- 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:
+    - rsyslog-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}}" or
+    add_repos | changed
   tags:
     - rsyslog-apt-packages