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Document the wonders of scale testing nova with the fake driver

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Devstack has some little known variables for running nova
with the fake compute driver and running several nova-compute
services on a single host, which can be useful for testing
move operations and scale testing of controller services like
nova-api and nova-scheduler.

This adds documentation about the fake virt driver and related
variables and scaling considerations when using them.

Change-Id: Ic89d463d0f3f180b323edd6e2c8ff0404638ef07
This commit is contained in:
Matt Riedemann 2019-02-28 17:30:47 -05:00
parent 72f632222f
commit 36773b262e
1 changed files with 66 additions and 0 deletions
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doc/source/guides/nova.rst
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@ -68,3 +68,69 @@ These config options are defined in `nova.conf.serial_console
For more information on OpenStack configuration see the `OpenStack
Compute Service Configuration Reference
<https://docs.openstack.org/nova/latest/admin/configuration/index.html>`_
Fake virt driver
================
Nova has a `fake virt driver`_ which can be used for scale testing the control
plane services or testing "move" operations between fake compute nodes, for
example cold/live migration, evacuate and unshelve.
The fake virt driver does not communicate with any hypervisor, it just reports
some fake resource inventory values and keeps track of the state of the
"guests" created, moved and deleted. It is not feature-complete with the
compute API but is good enough for most API testing, and is also used within
the nova functional tests themselves so is fairly robust.
.. _fake virt driver: http://git.openstack.org/cgit/openstack/nova/tree/nova/virt/fake.py
Configuration
-------------
Set the following in your devstack ``local.conf``:
.. code-block:: ini
[[local|localrc]]
VIRT_DRIVER=fake
NUMBER_FAKE_NOVA_COMPUTE=<number>
The ``NUMBER_FAKE_NOVA_COMPUTE`` variable controls the number of fake
``nova-compute`` services to run and defaults to 1.
When ``VIRT_DRIVER=fake`` is used, devstack will disable quota checking in
nova and neutron automatically. However, other services, like cinder, will
still enforce quota limits by default.
Scaling
-------
The actual value to use for ``NUMBER_FAKE_NOVA_COMPUTE`` depends on factors
such as:
* The size of the host (physical or virtualized) on which devstack is running.
* The number of API workers. By default, devstack will run ``max($nproc/2, 2)``
workers per API service. If you are running several fake compute services on
a single host, then consider setting ``API_WORKERS=1`` in ``local.conf``.
In addition, while quota will be disabled in neutron, there is no fake ML2
backend for neutron so creating fake VMs will still result in real ports being
created. To create servers without networking, you can specify ``--nic=none``
when creating the server, for example:
.. code-block:: shell
$ openstack --os-compute-api-version 2.37 server create --flavor cirros256 \
--image cirros-0.3.5-x86_64-disk --nic none --wait test-server
.. note:: ``--os-compute-api-version`` greater than or equal to 2.37 is
required to use ``--nic=none``.
To avoid overhead from other services which you may not need, disable them in
your ``local.conf``, for example:
.. code-block:: ini
disable_service horizon
disable_service tempest