LBaaS Driver Interface changes for new object model
Change-Id: I52ec8a7b6d7b562e151bd213eb82f701290063ba
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Doug Wiegley
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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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LBaaS Driver Interface changes for new Object Model
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===================================================
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Include the URL of your launchpad blueprint:
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https://blueprints.launchpad.net/neutron/+spec/lbaas-objmodel-driver-changes
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The upcoming LBaaS object model and API changes for Juno will require some
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driver interface changes, for new objects and backwards compatibility.
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New interfaces include create_load_balancer (and the rest of crud) and
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create_listener. Create_vip is going away, and will be supported in a shim
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layer for older drivers. M:N health monitor associations are also going away.
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The new object model and API blueprint:
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https://blueprints.launchpad.net/neutron/+spec/lbaas-api-and-objmodel-improvement
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This blueprint does not cover changes for the new TLS or L7 functionality.
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Problem description
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===================
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With the upcoming LBaaS object model and API changes, we will need new
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interfaces for the backend load balancing drivers, and a shim layer so that
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things continue to work with older drivers during a depcrecation period.
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Proposed change
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===============
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When loading the driver, neutron will determine if it is a new object model
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driver or an older legacy driver, and pick an appropriate implemenation/shim
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class depending on which.
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The new driver interface methods will be passed objects with attributes,
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instead of dictionaries as used in the icehouse drivers. For expediency's
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sake, initially these objects will be the standard neutron sqlalchemy objects,
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but full sqlalchemy functionality is not guaranteed in the future. Basic
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attributes and dependent object lookups will be supported long-term.
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The new driver interface will be made up of handler classes that implement
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create, update, and delete methods. Example, subject to change:
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sample_driver.py::
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class SampleDriver(LoadBalancerAbstractDriver):
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def __init__(self):
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self.load_balancer = MyLoadBalancerManager(self)
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self.listener = MyListener(self)
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self.member = ef.MemberHandler(self)
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self.stats = xyz.foo.StatsGatherer(self)
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self.health_monitor = HMHandler(self)
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class MyLoadBalancerManager(BaseManager):
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def __init__(self, driver):
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self.driver = driver
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def create(self, context, lb_obj):
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print("create")
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def update(self, context, lb_obj):
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print("update")
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def delete(self, context, lb_obj):
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print("delete")
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Supported driver handlers:
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* load_balancer
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* listener
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* pool
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* member
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* health_monitor
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* stats
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The following older driver methods will be translated/supported. Differences
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from existing behavior are noted next to each method.
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* create_vip - combination of one load_balancer and listener object from above.
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* update_vip
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* delete_vip
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* create_pool - first object created
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* update_pool
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* delete_pool
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* stats
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* create_member
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* update_member
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* delete_member
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* update_pool_health_monitor
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* create_pool_health_monitor
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* delete_pool_health_monitor
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Limitations of older driver shim:
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- Multiple listeners on a load balancer is not supported.
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- Multiple pools on a listener is not supported.
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- Many-to-many associations for health monitors is not supported.
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- Subnet id's on member objects are not supported.
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Driver breakage:
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- Some references to ldb.Vip will break until their maintainers update the
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relevant driver (embrane, radware). Tests for those drivers will be
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temporarily disabled until fixed.
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Alternatives
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------------
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One proposed alternative for the backwards compatibility shim layer for the
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drivers is to create a completely separate new LBaaS extension/plugin, with
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completely separate database tables, and let both exist. This would involve
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duplicate drivers and db tables. We decided not to use this approach, and
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the general implementation plan for the lbaas api/driver changes:
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* Create new LBaaS extension using database tables that have merged fields
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between old and new model.
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* Change front-end of old extension to "translate" into operations on new model.
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* Changer drivers to use new model.
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* Deprecate / delete unused old model fields from database.
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* Deprecate / delete old front-end.
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Data model impact
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-----------------
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None, refer to object model blueprint.
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REST API impact
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---------------
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None, refer to object model blueprint.
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Security impact
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---------------
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None, same impact as current driver implementations.
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Notifications impact
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--------------------
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None.
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Other end user impact
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---------------------
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None.
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Performance Impact
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------------------
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None, same impact as current driver implementations.
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Other deployer impact
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---------------------
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Upgrade to new LBaaS will involve a db migration; refer to object model
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blueprint. Older LBaaS drivers will continue to work, except that attempting
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to add multiple listeners to a load balancer will fail.
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Developer impact
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----------------
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Current LBaaS driver maintainers will need to eventually update their drivers
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to the new interface.
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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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https://launchpad.net/~brandon-logan
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https://launchpad.net/~dougwig
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Work Items
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----------
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- Modify layer above drivers to call new entry points.
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- Modify layer above drivers to call old driver interface methods for older
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drivers, translating the newer object model as needed.
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- New abstract_driver with new interfaces.
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Updating the reference haproxy driver will be in another blueprint.
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Dependencies
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============
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* https://blueprints.launchpad.net/neutron/+spec/lbaas-api-and-objmodel-improvement
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Testing
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=======
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- Existing tests against older drivers will continue to pass, unless testing
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the M:N health monitor relationship.
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- New tests will be added for new entry points will be added when the reference
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driver is updated.
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- Broken drivers, as specified in "Proposed change", will result in disabled
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tests until the drivers are fixed.
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Documentation Impact
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====================
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None.
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References
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==========
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* https://blueprints.launchpad.net/neutron/+spec/lbaas-api-and-objmodel-improvement
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* https://etherpad.openstack.org/p/1gsTm4GBdu
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* https://etherpad.openstack.org/p/juno-lbaas-mid-cycle-hackathon
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