openstack/openstack-manuals
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openstack-manuals/doc/ha-guide/source/environment-memcached.rst
KATO Tomoyuki d1fe08b4a7 [ha-guide] Reorganize basic services content 
To sync with installation guides.

Change-Id: Ia4df2bdb1f058bb3d8bcf035160463134d115384
Implements: blueprint improve-ha-guide
2016-05-24 07:17:39 +09:00

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Install memcached

[TODO: Verify that Oslo supports hash synchronization; if so, this should not take more than load balancing.]

[TODO: This hands off to two different docs for install information. We should choose one or explain the specific purpose of each.]

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.

To install and configure memcached, read the official documentation.

Memory caching is managed by oslo.cache so the way to use multiple memcached servers is the same for all projects.

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 does the job. For more information about memcached installation, see the OpenStack Administrator Guide.