e4f9185c54
This creates a new ha-guide-draft directory to allow developing the guide. Add infrastructure for: * The draft guide is not translated currently. * Build RST version (but not PDF yet) with each run. * Publish guide as draft * Update built index for it. Also updates the ToC to reflect the proposed changes. Implements: blueprint implement-ha-guide-todos Change-Id: If6f65646e02ac3eac08c288fd727ab9851cf9569
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1.9 KiB
ReStructuredText
53 lines
1.9 KiB
ReStructuredText
==================================
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Stateless versus stateful services
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==================================
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OpenStack components can be divided into three categories:
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- OpenStack APIs: APIs that are HTTP(s) stateless services written in python,
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easy to duplicate and mostly easy to load balance.
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- The SQL relational database server provides stateful type consumed by other
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components. Supported databases are MySQL, MariaDB, and PostgreSQL.
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Making the SQL database redundant is complex.
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- :term:`Advanced Message Queuing Protocol (AMQP)` provides OpenStack
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internal stateful communication service.
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.. to do: Ensure the difference between stateless and stateful services
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.. is clear
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Stateless services
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~~~~~~~~~~~~~~~~~~
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A service that provides a response after your request and then
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requires no further attention. To make a stateless service highly
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available, you need to provide redundant instances and load balance them.
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Stateless OpenStack services
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----------------------------
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OpenStack services that are stateless include ``nova-api``,
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``nova-conductor``, ``glance-api``, ``keystone-api``, ``neutron-api``,
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and ``nova-scheduler``.
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Stateful services
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~~~~~~~~~~~~~~~~~
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A service where subsequent requests to the service
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depend on the results of the first request.
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Stateful services are more difficult to manage because a single
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action typically involves more than one request. Providing
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additional instances and load balancing does not solve the problem.
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For example, if the horizon user interface reset itself every time
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you went to a new page, it would not be very useful.
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OpenStack services that are stateful include the OpenStack database
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and message queue.
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Making stateful services highly available can depend on whether you choose
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an active/passive or active/active configuration.
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Stateful OpenStack services
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----------------------------
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.. to do: create list of stateful services
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