openstack/openstack-manuals
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openstack-manuals/doc/ha-guide-draft/source/intro-os-ha-memcached.rst
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Change-Id: I39cabc18e40eee968309b63de3d74e3e828645d9
Signed-off-by: Doug Hellmann <doug@doughellmann.com>
2017-07-21 11:21:48 -04:00

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Memcached

Most OpenStack services can use Memcached to store ephemeral data such as tokens. Although Memcached does not support typical forms of redundancy such as clustering, OpenStack services can use almost any number of instances by configuring multiple hostnames or IP addresses.

The Memcached client implements hashing to balance objects among the instances. Failure of an instance only impacts a percentage of the objects, and the client automatically removes it from the list of instances.

Installation

To install and configure Memcached, read the official documentation.

Memory caching is managed by oslo.cache. This ensures consistency across all projects when using multiple Memcached servers. The following is an example configuration with three hosts:

Memcached_servers = controller1:11211,controller2:11211,controller3:11211

By default, controller1 handles the caching service. If the host goes down, controller2 or controller3 will complete the service.

For more information about Memcached installation, see the Environment -> Memcached section in the Installation Tutorials and Guides depending on your distribution.