Update documentation on overriding config files

The main motivation here is to document a mechanism which can be
used to configure Nova cells on a per-cell basis without introducing
a myriad of additional locations to put config files. The
following changes are made:

- Remove the note about only ini files being supported because
  merge_yaml is now used
- Expand on supported config file locations
- Add a section on using conditionals in the config file

Partially Implements: blueprint support-nova-cells
Change-Id: I92599e501506fdacaf3adb94cc6fffcf6fea2af3
This commit is contained in:
Doug Szumski 2019-09-10 17:35:28 +01:00
parent 651b983bdb
commit 98bed6c2bf

@ -157,10 +157,6 @@ in the ``/etc/kolla/certificates/`` directory.
OpenStack Service Configuration in Kolla
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.. note::
As of now kolla only supports config overrides for ini based configs.
An operator can change the location where custom config files are read from by
editing ``/etc/kolla/globals.yml`` and adding the following line.
@ -170,10 +166,29 @@ editing ``/etc/kolla/globals.yml`` and adding the following line.
node_custom_config: "/etc/kolla/config"
Kolla allows the operator to override configuration of services. Kolla will
look for a file in ``/etc/kolla/config/<< service name >>/<< config file >>``.
This can be done per-project, per-service or per-service-on-specified-host.
For example to override scheduler_max_attempts in nova scheduler, the operator
needs to create ``/etc/kolla/config/nova/nova-scheduler.conf`` with content:
generally look for a file in ``/etc/kolla/config/<< config file >>``,
``/etc/kolla/config/<< service name >>/<< config file >>`` or
``/etc/kolla/config/<< service name >>/<< hostname >>/<< config file >>``,
but these locations sometimes vary and you should check the config task in
the appropriate Ansible role for a full list of supported locations. For
example, in the case of ``nova.conf`` the following locations are supported,
assuming that you have services using ``nova.conf`` running on hosts
called ``controller-0001``, ``controller-0002`` and ``controller-0003``:
* ``/etc/kolla/config/nova.conf``
* ``/etc/kolla/config/nova/nova.conf``
* ``/etc/kolla/config/nova/controller-0001/nova.conf``
* ``/etc/kolla/config/nova/controller-0002/nova.conf``
* ``/etc/kolla/config/nova/controller-0003/nova.conf``
* ``/etc/kolla/config/nova/nova-scheduler.conf``
Using this mechansim, overrides can be configured per-project,
per-project-service or per-project-service-on-specified-host.
Overriding an option is as simple as setting the option under the relevant
section. For example, to set ``override scheduler_max_attempts`` in nova
scheduler, the operator could create
``/etc/kolla/config/nova/nova-scheduler.conf`` with content:
.. path /etc/kolla/config/nova/nova-scheduler.conf
.. code-block:: ini
@ -192,6 +207,40 @@ on host myhost, the operator needs to create file
cpu_allocation_ratio = 16.0
ram_allocation_ratio = 5.0
This method of merging configuration sections is supported for all services
using Oslo Config, which includes the vast majority of OpenStack services,
and in some cases for services using YAML configuration. Since the INI format
is an informal standard, not all INI files can be merged in this way. In
these cases Kolla supports overriding the entire config file.
Additional flexibility can be introduced by using Jinja conditionals in the
config files. For example, you may create Nova cells which are homogeneous
with respect to the hypervisor model. In each cell, you may wish to configure
the hypervisors differently, for example the following override shows one way
of setting the ``bandwidth_poll_interval`` variable as a function of the cell:
.. path /etc/kolla/config/nova.conf
.. code-block:: ini
[DEFAULT]
{% if 'cell0001' in group_names %}
bandwidth_poll_interval = 100
{% elif 'cell0002' in group_names %}
bandwidth_poll_interval = -1
{% else %}
bandwidth_poll_interval = 300
{% endif %}
An alternative to Jinja conditionals would be to define a variable for the
``bandwidth_poll_interval`` and set it in according to your requirements
in the inventory group or host vars:
.. path /etc/kolla/config/nova.conf
.. code-block:: ini
[DEFAULT]
bandwidth_poll_interval = {{ bandwidth_poll_interval }}
Kolla allows the operator to override configuration globally for all services.
It will look for a file called ``/etc/kolla/config/global.conf``.