Smarter updating of apt index during playbook execution

We can register changes when adding repositories and keys and then
update the apt package index conditionally. This should make it be
more consistent between initial host setup and subsequent re-runs.

roles/common/tasks/tarsnap.yml

@@ -1,12 +1,21 @@
 ---
 - name: Add Tarsnap apt mirror
   template: src=tarsnap_sources.list.j2 dest=/etc/apt/sources.list.d/tarsnap.list owner=root group=root mode=0644
+  register: add_tarsnap_apt_repository
   when: ansible_architecture != 'armv7l'
 
 - name: Add GPG key for Tarsnap
   apt_key: id=0x70BD6C50E82A9D99 url=https://pkg.tarsnap.com/tarsnap-deb-packaging-key.asc state=present
+  register: add_tarsnap_apt_key
   ignore_errors: yes
 
+- name: Update apt cache
+  apt:
+    update_cache: yes
+  when:
+    add_tarsnap_apt_key is changed or
+    add_tarsnap_apt_repository is changed
+
 - name: Install tarsnap
   apt: pkg=tarsnap update_cache=yes
 

roles/mariadb/tasks/main.yml

@@ -1,12 +1,21 @@
 ---
 - name: Add GPG key for MariaDB repo
   apt_key: id=0x177F4010FE56CA3336300305F1656F24C74CD1D8 url=https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x177F4010FE56CA3336300305F1656F24C74CD1D8
+  register: add_mariadb_apt_key
   tags: mariadb, packages
 
 - name: Add MariaDB 10.3 repo
   template: src=mariadb.list.j2 dest=/etc/apt/sources.list.d/mariadb.list owner=root group=root mode=0644
+  register: add_mariadb_apt_repository
   tags: mariadb, packages
 
+- name: Update apt cache
+  apt:
+    update_cache: yes
+  when:
+    add_mariadb_apt_key is changed or
+    add_mariadb_apt_repository is changed
+
 - name: Install mariadb-server
   apt: name={{ item }} state=present update_cache=yes
   loop:

roles/nginx/tasks/main.yml

@@ -1,12 +1,21 @@
 ---
 - name: Add nginx.org apt signing key
   apt_key: id=0x573BFD6B3D8FBC641079A6ABABF5BD827BD9BF62 url=https://nginx.org/keys/nginx_signing.key state=present
+  register: add_nginx_apt_key
   tags: nginx, packages
 
 - name: Add nginx.org repo
   template: src=nginx_org_sources.list.j2 dest=/etc/apt/sources.list.d/nginx_org_sources.list owner=root group=root mode=0644
+  register: add_nginx_apt_repository
   tags: nginx, packages
 
+- name: Update apt cache
+  apt:
+    update_cache: yes
+  when:
+    add_nginx_apt_key is changed or
+    add_nginx_apt_repository is changed
+
 - name: Install nginx
   apt: pkg=nginx update_cache=yes state=present
   tags: nginx, packages