docs: Add documentation on server groups
That's one giant hole in our docs. Whoops. Change-Id: I8ac6f204dd3ebe424dfe4335a491b8c9df7d0cc4 Signed-off-by: Stephen Finucane <stephenfin@redhat.com>
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@ -747,6 +747,8 @@ For example, when using the :command:`openstack server create` command, use the
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$ openstack server create --image IMAGE_ID --flavor 1 \
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$ openstack server create --image IMAGE_ID --flavor 1 \
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--hint group=SERVER_GROUP_UUID server-1
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--hint group=SERVER_GROUP_UUID server-1
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For more information on server groups, refer to :doc:`/user/server-groups`.
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.. _ServerGroupAntiAffinityFilter:
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.. _ServerGroupAntiAffinityFilter:
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@ -767,6 +769,8 @@ For example, when using the :command:`openstack server create` command, use the
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$ openstack server create --image IMAGE_ID --flavor 1 \
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$ openstack server create --image IMAGE_ID --flavor 1 \
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--hint group=SERVER_GROUP_UUID server-1
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--hint group=SERVER_GROUP_UUID server-1
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For more information on server groups, refer to :doc:`/user/server-groups`.
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``SimpleCIDRAffinityFilter``
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``SimpleCIDRAffinityFilter``
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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@ -15,6 +15,12 @@ zone feature. However, the implementation of these features differs vastly
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between these different services. Consult the documentation for these other
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between these different services. Consult the documentation for these other
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services for more information on their implementation of this feature.
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services for more information on their implementation of this feature.
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.. tip::
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Server Groups provide another mechanism for configuring the colocation of
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instances during scheduling. For more information, refer to
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:doc:`/user/server-groups`.
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Usage
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Usage
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-----
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-----
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@ -19,6 +19,7 @@ End user guide
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availability-zones
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availability-zones
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launch-instances
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launch-instances
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server-groups
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metadata
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metadata
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manage-ip-addresses
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manage-ip-addresses
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certificate-validation
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certificate-validation
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79
doc/source/user/server-groups.rst
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79
doc/source/user/server-groups.rst
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@ -0,0 +1,79 @@
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=============
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Server Groups
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=============
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Server groups provide a mechanism for indicating the locality of servers
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relative to other servers. They allow you to indicate whether servers should
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run on the same host (affinity) or different hosts (anti-affinity). Affinity is
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advantageous if you wish to minimise network latency, while anti-affinity can
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improve fault-tolerance and load distribution.
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.. note::
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Server groups are useful for separating or grouping workloads but should
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not generally be relied on to provide HA. Instead, consider using
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availability zones. Unlike server groups, availability zones can only be
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configured by admins but they are often used to model failure domains,
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particularly in larger deployments. For more information, refer to
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:doc:`/user/availability-zones`.
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Server groups can be configured with a policy and rules. There are currently
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four policies supported:
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``affinity``
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Restricts instances belonging to the server group to the same host.
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``anti-affinity``
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Restricts instances belonging to the server group to separate hosts.
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``soft-affinity``
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Attempts to restrict instances belonging to the server group to the same
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host. Where it is not possible to schedule all instances on one host,
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they will be scheduled together on as few hosts as possible.
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.. note::
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Requires API microversion 2.15 or later.
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``soft-anti-affinity``
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Attempts to restrict instances belonging to the server group to separate
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hosts. Where it is not possible to schedule all instances to separate hosts,
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they will be scheduled on as many separate hosts as possible.
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.. note::
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Requires API microversion 2.15 or later.
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There is currently one rule supported:
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``max_server_per_host``
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Indicates the max number of instances that can be scheduled to any given
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host when using the ``anti-affinity`` policy. This rule is not compatible
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with other policies.
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.. note::
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Requires API microversion 2.64 or later.
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Usage
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-----
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Server groups can be configured and used by end-users. For example:
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.. code-block:: console
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$ openstack --os-compute-api-version 2.64 server group create \
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--policy POLICY --rule RULE NAME
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Once a server group has been created, you can use it when creating a server.
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This is achieved using the ``--hint`` option. For example:
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.. code-block:: console
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$ openstack server create \
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--hint group=SERVER_GROUP_UUID ... NAME
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Once created, a server group cannot be modified. In addition, a server cannot
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move between server groups. In both cases, this is because doing so would
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require potentially moving the server to satisfy the server group policy.
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