Add nova cells appendix
Add an appendix detailing a nova cells deployment. Change-Id: Ic8373a59a93e86a97d4c1331e49a0024b86d499d
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Liam Young
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deploy-guide/source/app-nova-cells.rst
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deploy-guide/source/app-nova-cells.rst
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Appendix G: Additional Nova Cells
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=================================
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Overview
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++++++++
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Since Pike all OpenStack charm deployments have two cells: cell0 which is
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used to store instances which failed to get scheduled and cell1 which is an
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active compute cell. As of the 18.11 charm release multiple nova cells can be
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created when deploying a cloud or an existing deployment can be extended to
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add additional cells.
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Nova Cells v2 Topology
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++++++++++++++++++++++
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Nova cells v2 is entirely distinct from Nova cells v1. V1 has been deprecated
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and special care should be taken when reading nova documentation to ensure that
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it is v2 specific. Also, this is a *Nova* cell, other services such as
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.. note::
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This is a *Nova* cell, other services such as Neutron, Glance etc are not
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cell aware.
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The Super Conductor
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~~~~~~~~~~~~~~~~~~~
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For a deployment with multiple cells a dedicated conductor must be run for the
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API-level services. This conductor will have access to the API database and a
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dedicated message queue. This is called the super conductor to distinguish its
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place and purpose from the per-cell conductor nodes
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(See `Cells Layout <https://docs.openstack.org/nova/latest/user/cellsv2-layout.html#multiple-cells>`_.). The existing *nova-cloud-controller* charm already performs
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the role of the super conductor for the whole cloud and, in addition, acts as a
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cell conductor for cell1.
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nova-cell-controller charm
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~~~~~~~~~~~~~~~~~~~~~~~~~~
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A new *nova-cell-controller* charm has been created. This charm just runs the
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*nova-conductor* service and proxies some charm information, such as ssh keys,
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between the cell compute nodes and the super-conductor. An instance of
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*nova-cell-controller* is required per additional cell.
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Using application names to distinguish between cells
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Each cell requires the following charms:
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* nova-cell-controller
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* rabbitmq-server
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* percona-cluster
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* nova-compute
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To allow each application to be configured differently between cells and to
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be able to distinguish which instance of an application goes with which cell it
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is useful to add the cell name to the service name when deploying the
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components.
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.. code:: bash
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juju deploy nova-compute nova-compute-cell4
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Rabbit for Neutron
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~~~~~~~~~~~~~~~~~~
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One of the motivations for using cells is to help with scaling to a large
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number of compute nodes. While not a cells feature (nor a new feature) it is
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worth pointing out that the charms support breaking Neutron message traffic
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out onto a separate broker.
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.. code:: bash
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juju add-relation neutron-api:amqp rabbitmq-server-neutron:amqp
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juju add-relation neutron-gateway:amqp rabbitmq-server-neutron:amqp
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juju add-relation neutron-openvswitch:amqp rabbitmq-server-neutron:amqp
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juju add-relation ceilometer:amqp-listener rabbitmq-server-neutron:amqp
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Adding A New Cell to an Existing Deployment
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+++++++++++++++++++++++++++++++++++++++++++
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In an existing deployment cell1 already exists as do the services to support
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it. To add 'cell2' to this deployment the new cell applications need to be
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deployed and related to the existing applications.
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Add the four cell applications:
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.. code:: bash
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juju deploy cs:percona-cluster mysql-cell2
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juju deploy cs:rabbitmq-server rabbitmq-server-nova-cell2
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juju deploy cs:nova-compute nova-compute-cell2
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juju deploy cs:nova-cell-controller --config cell-name='cell2' nova-cell-controller-cell2
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Relate the new cell applications to each other:
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.. code:: bash
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juju add-relation nova-compute-cell2:amqp rabbitmq-server-nova-cell2:amqp
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juju add-relation nova-cell-controller-cell2:amqp rabbitmq-server-nova-cell2:amqp
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juju add-relation nova-cell-controller-cell2:shared-db mysql-cell2:shared-db
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juju add-relation nova-cell-controller-cell2:cloud-compute nova-compute-cell2:cloud-compute
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Relate the super conductor to the new cell:
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.. code:: bash
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juju add-relation nova-cloud-controller:nova-cell-api nova-cell-controller-cell2:nova-cell-compute
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juju add-relation nova-cloud-controller:amqp-cell rabbitmq-server-nova-cell2:amqp
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juju add-relation nova-cloud-controller:shared-db-cell mysql-cell2:shared-db
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Relate the new cell to network, image and identity services:
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.. code:: bash
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juju add-relation nova-compute-cell2:neutron-plugin neutron-openvswitch:neutron-plugin
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juju add-relation nova-compute-cell2:image-service glance:image-service
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juju add-relation nova-compute-cell2:cloud-credentials keystone:identity-credentials
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Relate the new cell to telemetry services.
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.. note::
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The ceilometer charm has an *amqp* and an *amqp-listerner* interface.
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ceilometer will listen and post messages to the broker related to the
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*amqp* interface. It will only listen to messages posted to the broker(s)
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related to the *amqp-listener*. Therefore services that consume messages
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from ceilometer, such as aodh, should be related to the broker associated
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with ceilometers *amqp* interface.
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.. code:: bash
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juju add-relation ceilometer:amqp-listener rabbitmq-server-nova-cell2:amqp
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juju add-relation ceilometer-agent:nova-ceilometer nova-compute-cell2:nova-ceilometer
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New Deployments
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+++++++++++++++
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For all cell deploymends ensure the following:
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* Application naming scheme such that the cell an application belongs to is
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clear.
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* Naming the central message broker such that its purpose is clear
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eg rabbitmq-server-general
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If cells is being used primarly to help with a large scale out of compute
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resources then in addition:
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* Do not relate compute nodes to the *nova-cloud-controller*
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* Have a separate message broker for Neutron.
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Below is an example of an overlay which can be used when doing a fresh deploy
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to add a second cell:
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.. code:: yaml
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applications:
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mysql-cell2:
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charm: cs:percona-cluster
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series: bionic
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num_units: 1
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options:
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max-connections: 1000
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nova-cell-controller-cell2:
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charm: cs:nova-cell-controller
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series: bionic
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num_units: 1
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options:
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cell-name: "cell2"
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nova-compute-cell2:
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charm: cs:nova-compute
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series: bionic
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num_units: 1
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constraints: mem=4G
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options:
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config-flags: default_ephemeral_format=ext4
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enable-live-migration: true
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enable-resize: true
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migration-auth-type: ssh
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rabbitmq-server-nova-cell2:
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charm: cs:rabbitmq-server
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num_units: 1
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relations:
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- - nova-compute-cell2:neutron-plugin
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- neutron-openvswitch:neutron-plugin
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- - nova-cloud-controller:amqp-cell
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- rabbitmq-server-nova-cell2:amqp
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- - ceilometer:amqp-listener
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- rabbitmq-server-nova-cell2
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- - ceilometer-agent
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- nova-compute-cell2
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- - nova-cloud-controller:nova-cell-api
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- nova-cell-controller-cell2:nova-cell-compute
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- - nova-cloud-controller:shared-db-cell
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- mysql-cell2:shared-db
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- - nova-cloud-controller:amqp-cell
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- rabbitmq-server-nova-cell2:amqp
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- - nova-compute-cell2:amqp
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- rabbitmq-server-nova-cell2:amqp
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- - nova-cell-controller-cell2:cloud-compute
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- nova-compute-cell2:cloud-compute
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- - nova-compute-cell2:image-service
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- glance:image-service
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- - nova-cell-controller-cell2:amqp
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- rabbitmq-server-nova-cell2:amqp
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- - nova-cell-controller-cell2:shared-db
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- mysql-cell2:shared-db
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- - nova-compute-cell2:cloud-credentials
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- keystone:identity-credentials
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Targeting instances at a cell
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Instances can be targetted at a specific cell by manually maintaining host
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aggregates and corresponding flavors which target those host aggregates. For
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example, assume *cell2* has one compute host *juju-250b86-prod-19*. Create a
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host aggregate for *cell2* and add the compute host into it.
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.. code:: bash
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openstack aggregate create --property cell=cell2 ag_cell2
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openstack aggregate add host ag_cell2 juju-250b86-prod-19
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Now create a flavor that targets that cell.
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.. code:: bash
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openstack flavor create --id 5 --ram 2048 --disk 10 --ephemeral 0 --vcpus 1 --public --property cell=cell2 m1.cell2.small
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Finally, enable the *AggregateInstanceExtraSpecsFilter*
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.. code:: bash
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FILTERS=$(juju config nova-cloud-controller scheduler-default-filters)
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juju config nova-cloud-controller scheduler-default-filters="${FILTERS},AggregateInstanceExtraSpecsFilter"
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Now instances that use the *m1.cell2.small* filter will land on cell2 compute
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hosts.
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.. note::
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These host aggregates need to be manually updated when compute nodes are
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added to the cell.
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@ -11,3 +11,4 @@ Appendices
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app-encryption-at-rest.rst
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app-certificate-management.rst
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app-series-upgrade.rst
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app-nova-cells.rst
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