ansible bootstrap variables cannot be overridden once for multiple hosts at the same time

[Allain Legacy]

Brief Description
-----------------
The Ansible bootstrap playbook defines some variables in host_vars/default.yml. Currently, those variables can be overridden on a per-host basis in an inventory_hostname.yml file. For variables that are, by nature, host specific that mechanism is fine, but there are variables that an end user may want to override on a per-site basis for many hosts without needing to manage the same change for many hosts. For example, a site may have local requirements for "dns_servers" or "docker_registries" so it would be more convenient to override those variables once in a single file and have that change apply to multiple hosts.

The main bootstrap.yml can be modified to insert an additional "include_vars" task to take variables from a site local file. See the following example where a new line has been inserted *before* the inventory_hostname include_vars task.

  pre_tasks:
    - include_vars: "{{ override_files_dir }}/secret"
      failed_when: false
    - include_vars: "{{ override_files_dir }}/site.yml"
      failed_when: false
    - include_vars: "{{ override_files_dir }}/{{ inventory_hostname }}.yml"
      failed_when: false

This order is important to ensure that an end user can still apply a per-host override that eclipses a per-site override.

Severity
--------
Minor

Steps to Reproduce
------------------
n/a

Expected Behavior
------------------
It should be possible to override one or more variables on a per-site basis using a single statement per variable.

Actual Behavior
----------------
A variable must be overridden for each host in the host inventory file.

Reproducibility
---------------
100%

System Configuration
--------------------
Any

Branch/Pull Time/Commit
-----------------------
June 7 latest build.

Last Pass
---------
Unknown

Timestamp/Logs
--------------
N/A

Test Activity
-------------
Developer testing

[Ghada Khalil (gkhalil)]

Enhancement/Optimization for ansible deployment; useful for deploying multiple systems at once. Marking as release gating given the benefit and the small code change

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/664608
Committed: https://git.openstack.org/cgit/starlingx/config/commit/?id=2905fd8bc0c0c03b4f7676448e76c78e980cc39d
Submitter: Zuul
Branch: master

commit 2905fd8bc0c0c03b4f7676448e76c78e980cc39d
Author: Allain Legacy <email address hidden>
Date: Tue Jun 11 07:54:58 2019 -0500

    playbookconfig: add variable include for site overrides

    Some playbook variables are site specific rather than host specific. For
    example "dns_servers" versus "external_oam_unit_0_address". It is
    cumbersome for an end user to have to override site specific variable in
    N different host files when it applies to all hosts in a specific site.

    The main play of the playbook is being extended to add an additional
    include so that a "site.yml" file can be imported with variable
    overrides specific to an entire site.

    The new "include_vars" is performed ahead of the host level
    "include_vars" so that if an end user still wants to override a site
    specific variable on a per-host basis that is still possible.

    Change-Id: I0ac49e9311af24d88d29dc381168a60c38f642cf
    Closes-Bug: #1832045
    Signed-off-by: Allain Legacy <email address hidden>