Moving .rst format files to main admin-guide-cloud folder
This change moves the .rst files into the main adming-guide-cloud folder now conversion is complete. changes to the project config and to the openstack manuals to stop sync of .xml files are also needed. Change-Id: I498e8d6ac3cb80da413e23b14a0959abd58e7d79 Implements: blueprint reorganise-user-guides
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Joseph Robinson
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Andreas Jaeger
Andreas Jaeger
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doc/admin-guide-cloud/source/compute-service-groups.rst
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doc/admin-guide-cloud/source/compute-service-groups.rst
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.. _configuring-compute-service-groups:
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================================
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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
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effectively manage and use them. This can include events like a user
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launching a new VM, the scheduler sending a request to a live node, or a
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query to the ServiceGroup API to determine if a node is live.
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When a compute worker running the nova-compute daemon starts, it calls
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the join API to join the compute group. Any service (such as the
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scheduler) can query the group's membership and the status of its nodes.
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Internally, the ServiceGroup client driver automatically updates the
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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.
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In a compute worker, this driver periodically sends a ``db update``
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command to the database, saying “I'm OK” with a timestamp. Compute uses
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a pre-defined timeout (``service_down_time``) to determine if a node is
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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
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database can be put under heavy load, which can cause the timeout to
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trigger, and a live node could incorrectly be considered dead. By
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default, the timeout is 60 seconds. Reducing the timeout value can help
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in this situation, but you must also make the database update more
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frequently, which again increases the database workload.
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The database contains data that is both transient (such as whether the
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node is alive) and persistent (such as entries for VM owners). With the
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ServiceGroup abstraction, Compute can treat each type separately.
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.. _zookeeper-servicegroup-driver:
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ZooKeeper ServiceGroup driver
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-----------------------------
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The ZooKeeper ServiceGroup driver works by using ZooKeeper ephemeral
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nodes. ZooKeeper, unlike databases, is a distributed system, with its
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load divided among several servers. On a compute worker node, the driver
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can establish a ZooKeeper session, then create an ephemeral znode in the
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group directory. Ephemeral znodes have the same lifespan as the session.
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If the worker node or the nova-compute daemon crashes, or a network
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partition is in place between the worker and the ZooKeeper server
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quorums, the ephemeral znodes are removed automatically. The driver
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can be given group membership by running the :command:`ls` command in the
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group directory.
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The ZooKeeper driver requires the ZooKeeper servers and client
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libraries. Setting up ZooKeeper servers is outside the scope of this
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guide (for more information, see `Apache Zookeeper <http://zookeeper.apache.org/>`_). These client-side
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Python libraries must be installed on every compute node:
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**python-zookeeper**
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The official Zookeeper Python binding
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**evzookeeper**
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This library makes the binding work with the eventlet threading model.
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This example assumes the ZooKeeper server addresses and ports are
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``192.168.2.1:2181``, ``192.168.2.2:2181``, and ``192.168.2.3:2181``.
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These values in the :file:`/etc/nova/nova.conf` file are required on every
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node for the ZooKeeper driver:
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.. code:: ini
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# Driver for the ServiceGroup service
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servicegroup_driver="zk"
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[zookeeper]
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address="192.168.2.1:2181,192.168.2.2:2181,192.168.2.3:2181"
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For Compute Service groups customization options, see the `OpenStack
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Configuration Reference Guide <http://docs.openstack.org/kilo/config-reference/
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content/list-of-compute-config-options.html#config_table_nova_zookeeper>`_.
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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
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object caching system that is used to increase site performance. For
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more details, see `memcached.org <http://memcached.org/>`_.
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To use the memcache driver, you must install memcached. You might
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already have it installed, as the same driver is also used for the
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OpenStack Object Storage and OpenStack dashboard. If you need to install
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memcached, see the instructions in the `OpenStack Installation Guide <http://docs.openstack.org/>`_.
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These values in the :file:`/etc/nova/nova.conf` file are required on every
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node for the memcache driver:
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.. code:: 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
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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
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(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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