310 lines
12 KiB
ReStructuredText
310 lines
12 KiB
ReStructuredText
==================================================
|
||
Customizing the OpenStack Compute (nova) Scheduler
|
||
==================================================
|
||
|
||
Many OpenStack projects allow for customization of specific features
|
||
using a driver architecture. You can write a driver that conforms to a
|
||
particular interface and plug it in through configuration. For example,
|
||
you can easily plug in a new scheduler for Compute. The existing
|
||
schedulers for Compute are feature full and well documented at `Scheduling
|
||
<https://docs.openstack.org/ocata/config-reference/compute/schedulers.html>`_.
|
||
However, depending on your user's use cases, the existing schedulers
|
||
might not meet your requirements. You might need to create a new scheduler.
|
||
|
||
To create a scheduler, you must inherit from the class
|
||
``nova.scheduler.driver.Scheduler``. Of the five methods that you can
|
||
override, you *must* override the two methods marked with an asterisk
|
||
(\*) below:
|
||
|
||
- ``update_service_capabilities``
|
||
|
||
- ``hosts_up``
|
||
|
||
- ``group_hosts``
|
||
|
||
- \* ``schedule_run_instance``
|
||
|
||
- \* ``select_destinations``
|
||
|
||
To demonstrate customizing OpenStack, we'll create an example of a
|
||
Compute scheduler that randomly places an instance on a subset of hosts,
|
||
depending on the originating IP address of the request and the prefix of
|
||
the hostname. Such an example could be useful when you have a group of
|
||
users on a subnet and you want all of their instances to start within
|
||
some subset of your hosts.
|
||
|
||
.. warning::
|
||
|
||
This example is for illustrative purposes only. It should not be
|
||
used as a scheduler for Compute without further development and
|
||
testing.
|
||
|
||
When you join the screen session that ``stack.sh`` starts with
|
||
``screen -r stack``, you are greeted with many screen windows:
|
||
|
||
.. code-block:: console
|
||
|
||
0$ shell* 1$ key 2$ horizon ... 9$ n-api ... 14$ n-sch ...
|
||
|
||
|
||
``shell``
|
||
A shell where you can get some work done
|
||
|
||
``key``
|
||
The keystone service
|
||
|
||
``horizon``
|
||
The horizon dashboard web application
|
||
|
||
``n-{name}``
|
||
The nova services
|
||
|
||
``n-sch``
|
||
The nova scheduler service
|
||
|
||
**To create the scheduler and plug it in through configuration**
|
||
|
||
#. The code for OpenStack lives in ``/opt/stack``, so go to the ``nova``
|
||
directory and edit your scheduler module. Change to the directory where
|
||
``nova`` is installed:
|
||
|
||
.. code-block:: console
|
||
|
||
$ cd /opt/stack/nova
|
||
|
||
#. Create the ``ip_scheduler.py`` Python source code file:
|
||
|
||
.. code-block:: console
|
||
|
||
$ vim nova/scheduler/ip_scheduler.py
|
||
|
||
#. The code shown below is a driver that will
|
||
schedule servers to hosts based on IP address as explained at the
|
||
beginning of the section. Copy the code into ``ip_scheduler.py``. When
|
||
you are done, save and close the file.
|
||
|
||
.. code-block:: python
|
||
|
||
# vim: tabstop=4 shiftwidth=4 softtabstop=4
|
||
# Copyright (c) 2014 OpenStack Foundation
|
||
# All Rights Reserved.
|
||
#
|
||
# Licensed under the Apache License, Version 2.0 (the "License"); you may
|
||
# not use this file except in compliance with the License. You may obtain
|
||
# a copy of the License at
|
||
#
|
||
# http://www.apache.org/licenses/LICENSE-2.0
|
||
#
|
||
# Unless required by applicable law or agreed to in writing, software
|
||
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
|
||
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
|
||
# License for the specific language governing permissions and limitations
|
||
# under the License.
|
||
|
||
"""
|
||
IP Scheduler implementation
|
||
"""
|
||
|
||
import random
|
||
|
||
from oslo_config import cfg
|
||
|
||
from nova.compute import rpcapi as compute_rpcapi
|
||
from nova import exception
|
||
from nova.openstack.common import log as logging
|
||
from nova.openstack.common.gettextutils import _
|
||
from nova.scheduler import driver
|
||
|
||
CONF = cfg.CONF
|
||
CONF.import_opt('compute_topic', 'nova.compute.rpcapi')
|
||
LOG = logging.getLogger(__name__)
|
||
|
||
class IPScheduler(driver.Scheduler):
|
||
"""
|
||
Implements Scheduler as a random node selector based on
|
||
IP address and hostname prefix.
|
||
"""
|
||
|
||
def __init__(self, *args, **kwargs):
|
||
super(IPScheduler, self).__init__(*args, **kwargs)
|
||
self.compute_rpcapi = compute_rpcapi.ComputeAPI()
|
||
|
||
def _filter_hosts(self, request_spec, hosts, filter_properties,
|
||
hostname_prefix):
|
||
"""Filter a list of hosts based on hostname prefix."""
|
||
|
||
hosts = [host for host in hosts if host.startswith(hostname_prefix)]
|
||
return hosts
|
||
|
||
def _schedule(self, context, topic, request_spec, filter_properties):
|
||
"""Picks a host that is up at random."""
|
||
|
||
elevated = context.elevated()
|
||
hosts = self.hosts_up(elevated, topic)
|
||
if not hosts:
|
||
msg = _("Is the appropriate service running?")
|
||
raise exception.NoValidHost(reason=msg)
|
||
|
||
remote_ip = context.remote_address
|
||
|
||
if remote_ip.startswith('10.1'):
|
||
hostname_prefix = 'doc'
|
||
elif remote_ip.startswith('10.2'):
|
||
hostname_prefix = 'ops'
|
||
else:
|
||
hostname_prefix = 'dev'
|
||
|
||
hosts = self._filter_hosts(request_spec, hosts, filter_properties,
|
||
hostname_prefix)
|
||
if not hosts:
|
||
msg = _("Could not find another compute")
|
||
raise exception.NoValidHost(reason=msg)
|
||
|
||
host = random.choice(hosts)
|
||
LOG.debug("Request from %(remote_ip)s scheduled to %(host)s" % locals())
|
||
|
||
return host
|
||
|
||
def select_destinations(self, context, request_spec, filter_properties):
|
||
"""Selects random destinations."""
|
||
num_instances = request_spec['num_instances']
|
||
# NOTE(timello): Returns a list of dicts with 'host', 'nodename' and
|
||
# 'limits' as keys for compatibility with filter_scheduler.
|
||
dests = []
|
||
for i in range(num_instances):
|
||
host = self._schedule(context, CONF.compute_topic,
|
||
request_spec, filter_properties)
|
||
host_state = dict(host=host, nodename=None, limits=None)
|
||
dests.append(host_state)
|
||
|
||
if len(dests) < num_instances:
|
||
raise exception.NoValidHost(reason='')
|
||
return dests
|
||
|
||
def schedule_run_instance(self, context, request_spec,
|
||
admin_password, injected_files,
|
||
requested_networks, is_first_time,
|
||
filter_properties, legacy_bdm_in_spec):
|
||
"""Create and run an instance or instances."""
|
||
instance_uuids = request_spec.get('instance_uuids')
|
||
for num, instance_uuid in enumerate(instance_uuids):
|
||
request_spec['instance_properties']['launch_index'] = num
|
||
try:
|
||
host = self._schedule(context, CONF.compute_topic,
|
||
request_spec, filter_properties)
|
||
updated_instance = driver.instance_update_db(context,
|
||
instance_uuid)
|
||
self.compute_rpcapi.run_instance(context,
|
||
instance=updated_instance, host=host,
|
||
requested_networks=requested_networks,
|
||
injected_files=injected_files,
|
||
admin_password=admin_password,
|
||
is_first_time=is_first_time,
|
||
request_spec=request_spec,
|
||
filter_properties=filter_properties,
|
||
legacy_bdm_in_spec=legacy_bdm_in_spec)
|
||
except Exception as ex:
|
||
# NOTE(vish): we don't reraise the exception here to make sure
|
||
# that all instances in the request get set to
|
||
# error properly
|
||
driver.handle_schedule_error(context, ex, instance_uuid,
|
||
request_spec)
|
||
|
||
There is a lot of useful information in ``context``, ``request_spec``,
|
||
and ``filter_properties`` that you can use to decide where to schedule
|
||
the instance. To find out more about what properties are available, you
|
||
can insert the following log statements into the
|
||
``schedule_run_instance`` method of the scheduler above:
|
||
|
||
.. code-block:: python
|
||
|
||
LOG.debug("context = %(context)s" % {'context': context.__dict__})
|
||
LOG.debug("request_spec = %(request_spec)s" % locals())
|
||
LOG.debug("filter_properties = %(filter_properties)s" % locals())
|
||
|
||
#. To plug this scheduler into nova, edit one configuration file,
|
||
``/etc/nova/nova.conf``:
|
||
|
||
.. code-block:: console
|
||
|
||
$ vim /etc/nova/nova.conf
|
||
|
||
#. Find the ``scheduler_driver`` config and change it like so:
|
||
|
||
.. code-block:: ini
|
||
|
||
scheduler_driver=nova.scheduler.ip_scheduler.IPScheduler
|
||
|
||
#. Restart the nova scheduler service to make nova use your scheduler.
|
||
Start by switching to the ``n-sch`` screen:
|
||
|
||
#. Press **Ctrl+A** followed by **9**.
|
||
|
||
#. Press **Ctrl+A** followed by **N** until you reach the ``n-sch`` screen.
|
||
|
||
#. Press **Ctrl+C** to kill the service.
|
||
|
||
#. Press **Up Arrow** to bring up the last command.
|
||
|
||
#. Press **Enter** to run it.
|
||
|
||
#. Test your scheduler with the nova CLI. Start by switching to the
|
||
``shell`` screen and finish by switching back to the ``n-sch`` screen to
|
||
check the log output:
|
||
|
||
#. Press **Ctrl+A** followed by **0**.
|
||
|
||
#. Make sure you are in the ``devstack`` directory:
|
||
|
||
.. code-block:: console
|
||
|
||
$ cd /root/devstack
|
||
|
||
#. Source ``openrc`` to set up your environment variables for the CLI:
|
||
|
||
.. code-block:: console
|
||
|
||
$ . openrc
|
||
|
||
#. Put the image ID for the only installed image into an environment
|
||
variable:
|
||
|
||
.. code-block:: console
|
||
|
||
$ IMAGE_ID=`openstack image list | egrep cirros | egrep -v "kernel|ramdisk" | awk '{print $2}'`
|
||
|
||
#. Boot a test server:
|
||
|
||
.. code-block:: console
|
||
|
||
$ openstack server create --flavor 1 --image $IMAGE_ID scheduler-test
|
||
|
||
#. Switch back to the ``n-sch`` screen. Among the log statements, you'll
|
||
see the line:
|
||
|
||
.. code-block:: console
|
||
|
||
2014-01-23 19:57:47.262 DEBUG nova.scheduler.ip_scheduler
|
||
[req-... demo demo] Request from xx.xx.xx.xx scheduled to devstack-havana
|
||
_schedule /opt/stack/nova/nova/scheduler/ip_scheduler.py:76
|
||
|
||
.. warning::
|
||
|
||
Functional testing like this is not a replacement for proper unit
|
||
and integration testing, but it serves to get you started.
|
||
|
||
A similar pattern can be followed in other projects that use the driver
|
||
architecture. Simply create a module and class that conform to the
|
||
driver interface and plug it in through configuration. Your code runs
|
||
when that feature is used and can call out to other services as
|
||
necessary. No project core code is touched. Look for a "driver" value in
|
||
the project's ``.conf`` configuration files in ``/etc/<project>`` to
|
||
identify projects that use a driver architecture.
|
||
|
||
When your scheduler is done, we encourage you to open source it and let
|
||
the community know on the OpenStack mailing list. Perhaps others need
|
||
the same functionality. They can use your code, provide feedback, and
|
||
possibly contribute. If enough support exists for it, perhaps you can
|
||
propose that it be added to the official Compute
|
||
`schedulers <https://git.openstack.org/cgit/openstack/nova/tree/nova/scheduler>`_.
|