Support for fine-grained distro-related defaults

Currently, we specify defaults for the RedHat and Ubuntu
distribution families, and perform adjustments to these
in the playbooks based on checks for OS version, etc.
This is awkward. Instead, import defaults files in increasing
order of specificity to tune the install for each distribution
and version without extra playbook items.

Change-Id: I60b5a1f1c1f63fe4c742599a5a8a12a80cd15652

playbooks/roles/bifrost-ironic-install/README.md

@@ -77,6 +77,29 @@ mainly limited to settings which are unlikely to be modified, unless a user
 has a custom Ironic Python Agent image, or needs to modify where the httpboot
 folder is set to.
 
+This role has several variables that can vary between OS families,
+distributions, and their specific versions. These are specified in the
+required_defaults_* files.  They are imported in a particular
+order. For example, for Ubuntu 15.04, the role will attempt to import
+the following files:
+
+- required_defaults_Debian.yml
+- required_defaults_Ubuntu.yml
+- required_defaults_Ubuntu_15.04.yml
+
+Not all of the possible files for a given distribution/version combination
+need to exist. The recommended approach for adding a new variable is:
+
+- Put the variable in the most generic set of defaults to which it applies:
+  for example, if a given variable is applicable to all Debian-family OSes,
+  put it in required_defaults_Debian.yml
+
+- Variables specified in the more specific files will be used to override
+  values in the more generic defaults files.
+
+- If a given default applies to multiple versions of a distribution, that
+  variable needs to be specified for each version which it affects.
+
 Dependencies
 ------------
 

playbooks/roles/bifrost-ironic-install/defaults/dummy-defaults.yml

@@ -0,0 +1,3 @@
+---
+# NOTE(cinerama) This file is intentionally left blank - do not
+# add variables here.

playbooks/roles/bifrost-ironic-install/defaults/required_defaults_Fedora_22.yml

@@ -0,0 +1,5 @@
+---
+# NOTE(cinerama): On Fedora 22, ansible 1.9, ansible_pkg_mgr
+# defaults to yum, which may not be installed. This can be safely
+# removed when we start using an ansible release which prefers dnf.
+ansible_pkg_mgr: "dnf"

playbooks/roles/bifrost-ironic-install/defaults/required_defaults_Ubuntu_15.04.yml

@@ -0,0 +1,4 @@
+---
+init_template: systemd_template.j2
+init_dest_dir: /lib/systemd/system/
+init_ext: .service

playbooks/roles/bifrost-ironic-install/tasks/main.yml

@@ -13,24 +13,27 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 ---
-- name: Include OS-specific packages variables.
+# NOTE(cinerama) dummy-defaults.yml is an empty defaults file. We use it
+# here to ensure that with_first_found won't fail should we not have
+# defaults for a particular distribution, version, etc.
+- name: Include OS family-specific defaults
+  include_vars: "{{ item }}"
+  with_first_found:
+    - "../defaults/required_defaults_{{ ansible_os_family }}_family.yml"
+    - "../defaults/dummy-defaults.yml"
+- name: Include OS distribution-specific defaults
   include_vars: "{{ item }}"
   with_first_found:
     - "../defaults/required_defaults_{{ ansible_distribution }}.yml"
-    - "../defaults/required_defaults_{{ ansible_os_family }}.yml"
+    - "../defaults/dummy-defaults.yml"
+- name: Include OS version-specific defaults
+  include_vars: "{{ item }}"
+  with_first_found:
+    - "../defaults/required_defaults_{{ ansible_distribution }}_{{ ansible_distribution_version }}.yml"
+    - "../defaults/dummy-defaults.yml"
 - name: "Update Package Cache"
   apt: update_cache=yes
   when: ansible_os_family == 'Debian'
-# NOTE(cinerama): On Fedora 22, ansible 1.9, ansible_pkg_mgr
-# defaults to yum, which may not be installed. This can be safely
-# removed when we start using an ansible release which prefers dnf.
-- name: "Check for dnf"
-  stat: path=/usr/bin/dnf
-  register: test_dnf
-- name: "Adjust ansible_pkg_mgr if dnf exists"
-  set_fact:
-    ansible_pkg_mgr: "dnf"
-  when: ansible_distribution == 'Fedora' and "{{ test_dnf.stat.exists|bool }}"
 - name: "Install packages"
   action: "{{ ansible_pkg_mgr }} name={{ item }}"
   with_items: required_packages
@@ -146,12 +149,6 @@
 - name: "Creating authorized_keys file for ironic user"
   command: cp -p /home/ironic/.ssh/id_rsa.pub /home/ironic/.ssh/authorized_keys
   when: testing == true
-- name: "Adjust init vars for Ubuntu >= 15.04, which is systemd"
-  set_fact:
-    init_template: systemd_template.j2
-    init_dest_dir: /lib/systemd/system/
-    init_ext: .service
-  when: ansible_distribution_version|version_compare('15.04', '>=') and ansible_distribution == 'Ubuntu'
 - name: "Placing services"
   template: src={{ init_template }} dest={{ init_dest_dir }}{{item.service_name}}{{ init_ext }} owner=root group=root
   with_items: