Pacemaker provider for Openstack services
Change-Id: I753cc4e1f7561df06fd6391c5c8b6a5fced759e8
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Bogdan Dobrelya
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specs/5.0.0/pacemaker-provider-for-openstack.rst
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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==========================================
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Pacemaker provider for Openstack services
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==========================================
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https://blueprints.launchpad.net/puppet-nova/+spec/pacemaker-provider-for-openstack
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It is a common practice to make services managed by Pacemaker in Linux HA clusters.
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Puppet modules for Openstack should be able to ensure both standard and Pacemaker
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providers for Openstack services as well.
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In order to achieve this as a transparent solution (w/o modifications to the core
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Puppet modules for Openstack) special wrapping classes should be created in
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puppet-openstack_extras. These wrappers should contain overrides for Openstack
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services as a Pacemaker service provider and ensure creation of corresponding
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Pacemaker resources as well.
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Problem description
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===================
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A detailed description of the problem:
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Puppet modules for Openstack configure services in a classic way, such as
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system service providers.
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For HA clusters, though, operators might have wanted to have an option
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to delegate Openstack services management for Pacemaker instead.
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Pacemaker OCF scripts provide very good options for cluster-wide resources
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management and Puppet should deliver this options as well.
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Proposed change
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===============
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A Pacemaker service provider and special wrapper class or classes, like
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``openstack_extras::pacemaker::heat`` or ``openstack_extras::pacemaker::nova``
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should be created as well as Resource Agents (OCF) scripts for related cluster
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resources management. Once a wrapper class is included in the Puppet catalog,
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it would override the default service provider of the corresponding Openstack
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service configured by its base core module. That will ensure a transparent way
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of HA configuration for Openstack services without any modifications to the
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base core modules, such as puppet-nova or puppet-heat and so on.
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For the first stage of implementation, there should be only a service provider
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for Pacemaker created and put into the openstack_extras. That will assume the
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deployers should use their own custom classes and Resource Agents (OCF) scripts
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for the cluster resources configuration.
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The second stage should be a creation of a basic HA wrapper class (or classes)
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shipped with a generic OCF scripts for the cluster resources definition which
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could benefit every developer. Of course, there should be a way for deployer
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to use his custom OCF scripts as well.
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Note, that Puppet modules for Openstack will not configure Openstack services
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in HA by default. Also, related infra services (such as MySQL or RabbitMQ)
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should not be configured by Puppet Openstack core modules, so we do not expect
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it for HA provider as well. But HA provider still could be used to do so,
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if user wants to override some basic service provider to HA one. By design,
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it should work transparently for whichever service in Puppet catalog.
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The module for Pacemaker and Corosync to be used with this HA provider is a
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puppetlabs/corosync.
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Alternatives
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------------
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The another option is to use puppet-openstacklibs instead of extras.
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There is also an option to switch to another module for Pacemaker and Corosync
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instead of puppetlabs/corosync. The former one does not support clones,
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location constraints, operates via pcs/crmsh CLI which are not good then cluster
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is being deoplyed in parallel. So, it could make sence to redesign it
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completely, or switch from it to another module, or provide an option to specify
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which module deployer wants to use.
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A completely another approach could be considered as well.
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Pacemaker provider configuration could be ensured as a simple pipe, i.e. we
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are passing a some external class name (and its params as a hash) into the
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corresponding Openstack classes. This approach resembles the one for
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``rabbitmq_class`` which uses ``rabbitmq::server`` as a default value but
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could be anything else. But for this case it should be some Pacemaker or
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Corosync related class instead.
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Each Openstack class providing the service should be as well extended then
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with the following parameters:
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* ``pacemaker_provider`` (or ``ha-mode``) type parameter. The default value
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should be ``false`` for backward compatibility reasons.
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* ``corosync_class`` or ``pacemaker_class`` reference to a some external
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class which should be used for Corosync (Pacemaker) resources definition.
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The default value should be ``false`` for backward compatibility reasons.
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* One for ``resource_hash`` parameters being passed into the aforementioned
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class above.
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Data model impact
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-----------------
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None
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Module API impact
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-----------------
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None
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End user impact
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---------------------
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The user will be able to configure Openstack services in a much
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more flexible and Highly available way.
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Performance Impact
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------------------
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There would be no performance impact, if default service provider for
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Openstack services is used. The performance of Pacemaker provider is
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deeply tight with the Pacemaker or Corosync Puppet module chosen by
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the user. Anyway, the cluster resources definition for services should
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be done only once, hence the performance impact will be the minimal in
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overall deployment process and near to none in later operations.
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Deployer impact
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---------------------
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The deployment behavior will not change at all for the case with wrapper
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classes in puppet-openstack_extras (openstacklibs).
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The only action required would be to include a wrapper classes for Openstack
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services in catalog in order to ensure Pacemaker provider for them.
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For the approach with an external class reference, the deployer would
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have to provide a valid Pacemaker or Corosync class reference for some
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external module in catalog and a valid hash of parameters for it.
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Developer impact
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----------------
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None
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Implementation
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==============
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Assignee(s)
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-----------
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Primary assignee:
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bogdando <bdobrelia@mirantis.com>
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Other contributors:
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idv1985 <dilyin@mirantis.com>
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Work Items
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----------
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* Create a service provider for Pacemaker (HA provider) as a part of the
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openstack_extras.
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* Create a basic HA wrapper classes shipped with a generic OCF scripts for
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the cluster resources definition and an option to specify a custom OCF
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scripts as well.
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* Describe in documentation how HA provider could be used with Puppet modules
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for Openstack to configure Openstack services in HA.
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* (optional) Describe in documentation how HA provider could be used to
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configure related services, such as RabbitMQ and MySQL in HA.
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Dependencies
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============
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None
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Testing
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=======
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The feature should be tested with the rspecs provided.
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Documentation Impact
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====================
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The feature should be described in the docs for puppet-openstack_extras
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(or openstacklibs) module or core Puppet modules for Openstack for the case
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with external Corosync (Pacemaker) classes.
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New wrapper classes should be described and usage examples provided.
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References
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==========
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None
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