68 lines
2.9 KiB
ReStructuredText
68 lines
2.9 KiB
ReStructuredText
================================
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Configure Compute service groups
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================================
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The Compute service must know the status of each compute node to effectively
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manage and use them. This can include events like a user launching a new VM,
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the scheduler sending a request to a live node, or a query to the ServiceGroup
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API to determine if a node is live.
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When a compute worker running the nova-compute daemon starts, it calls the join
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API to join the compute group. Any service (such as the scheduler) can query
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the group's membership and the status of its nodes. Internally, the
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ServiceGroup client driver automatically updates the compute worker status.
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.. _database-servicegroup-driver:
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Database ServiceGroup driver
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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By default, Compute uses the database driver to track if a node is live. In a
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compute worker, this driver periodically sends a ``db update`` command to the
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database, saying “I'm OK” with a timestamp. Compute uses a pre-defined
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timeout (``service_down_time``) to determine if a node is dead.
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The driver has limitations, which can be problematic depending on your
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environment. If a lot of compute worker nodes need to be checked, the database
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can be put under heavy load, which can cause the timeout to trigger, and a live
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node could incorrectly be considered dead. By default, the timeout is 60
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seconds. Reducing the timeout value can help in this situation, but you must
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also make the database update more frequently, which again increases the
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database workload.
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The database contains data that is both transient (such as whether the node is
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alive) and persistent (such as entries for VM owners). With the ServiceGroup
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abstraction, Compute can treat each type separately.
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.. _memcache-servicegroup-driver:
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Memcache ServiceGroup driver
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The memcache ServiceGroup driver uses memcached, a distributed memory object
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caching system that is used to increase site performance. For more details, see
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`memcached.org <http://memcached.org/>`_.
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To use the memcache driver, you must install memcached. You might already have
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it installed, as the same driver is also used for the OpenStack Object Storage
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and OpenStack dashboard. To install memcached, see the *Environment ->
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Memcached* section in the `Installation Tutorials and Guides
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<https://docs.openstack.org/project-install-guide/ocata>`_ depending on your
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distribution.
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These values in the ``/etc/nova/nova.conf`` file are required on every node for
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the memcache driver:
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.. code-block:: ini
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# Driver for the ServiceGroup service
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servicegroup_driver = "mc"
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# Memcached servers. Use either a list of memcached servers to use for caching (list value),
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# or "<None>" for in-process caching (default).
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memcached_servers = <None>
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# Timeout; maximum time since last check-in for up service (integer value).
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# Helps to define whether a node is dead
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service_down_time = 60
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