Addning handler for Nginx config validation:

Although the 'validate' param was added for the deployment of
/etc/nginx.conf - this validation process will only be triggered upon
changes.
So, if a vhost config is updated, but the main config isn't, the
collective config will not be verified.

I've added a new handler 'validate nginx configuration' and added this
to the 'notify' param as a first list item for vhost config changes.

Unfortunately, this will not protect against the deployment of malformed
configuration, however it will prevent the restart of Nginx in such a
situation (as the 'validate nginx configuration' handler should error
out before the 'restart nginx' handler is called).

handlers/main.yml

@@ -1,3 +1,7 @@
 ---
 - name: restart nginx
   service: name=nginx state=restarted
+
+- name: validate nginx configuration
+  command: nginx -t -c /etc/nginx.conf
+  changed_when: False

tasks/vhosts.yml

@@ -12,11 +12,16 @@
     dest: "{{ nginx_vhost_path }}/vhosts.conf"
     mode: 0644
   when: nginx_vhosts|length > 0
-  notify: restart nginx
+  notify:
+    - validate nginx configuration
+    - restart nginx
 
 - name: Remove managed vhost config file (if no vhosts are configured).
   file:
     path: "{{ nginx_vhost_path }}/vhosts.conf"
     state: absent
   when: nginx_vhosts|length == 0
-  notify: restart nginx
+  notify:
+    - validate nginx configuration
+    - restart nginx
+