Bob, this is fantastic, I really appreciate all the detail. A couple of questions ...
On Wed, Feb 05, at 2:16 am, Robert Kukura <rkuk...@redhat.com> wrote: > A couple of interrelated issues with the ML2 plugin's port binding have > been discussed over the past several months in the weekly ML2 meetings. > These effect drivers being implemented for icehouse, and therefore need > to be addressed in icehouse: > > * MechanismDrivers need detailed information about all binding changes, > including unbinding on port deletion > (https://bugs.launchpad.net/neutron/+bug/1276395) > * MechanismDrivers' bind_port() methods are currently called inside > transactions, but in some cases need to make remote calls to controllers > or devices (https://bugs.launchpad.net/neutron/+bug/1276391) > * Semantics of concurrent port binding need to be defined if binding is > moved outside the triggering transaction. > > I've taken the action of writing up a unified proposal for resolving > these issues, which follows... > > 1) An original_bound_segment property will be added to PortContext. When > the MechanismDriver update_port_precommit() and update_port_postcommit() > methods are called and a binding previously existed (whether its being > torn down or not), this property will provide access to the network > segment used by the old binding. In these same cases, the portbinding > extension attributes (such as binding:vif_type) for the old binding will > be available via the PortContext.original property. It may be helpful to > also add bound_driver and original_bound_driver properties to > PortContext that behave similarly to bound_segment and > original_bound_segment. > > 2) The MechanismDriver.bind_port() method will no longer be called from > within a transaction. This will allow drivers to make remote calls on > controllers or devices from within this method without holding a DB > transaction open during those calls. Drivers can manage their own > transactions within bind_port() if needed, but need to be aware that > these are independent from the transaction that triggered binding, and > concurrent changes to the port could be occurring. > > 3) Binding will only occur after the transaction that triggers it has > been completely processed and committed. That initial transaction will > unbind the port if necessary. Four cases for the initial transaction are > possible: > > 3a) In a port create operation, whether the binding:host_id is supplied > or not, all drivers' port_create_precommit() methods will be called, the > initial transaction will be committed, and all drivers' > port_create_postcommit() methods will be called. The drivers will see > this as creation of a new unbound port, with PortContext properties as > shown. If a value for binding:host_id was supplied, binding will occur > afterwards as described in 4 below. > > PortContext.original: None > PortContext.original_bound_segment: None > PortContext.original_bound_driver: None > PortContext.current['binding:host_id']: supplied value or None > PortContext.current['binding:vif_type']: 'unbound' > PortContext.bound_segment: None > PortContext.bound_driver: None > > 3b) Similarly, in a port update operation on a previously unbound port, > all drivers' port_update_precommit() and port_update_postcommit() > methods will be called, with PortContext properies as shown. If a value > for binding:host_id was supplied, binding will occur afterwards as > described in 4 below. > > PortContext.original['binding:host_id']: previous value or None > PortContext.original['binding:vif_type']: 'unbound' or 'binding_failed' > PortContext.original_bound_segment: None > PortContext.original_bound_driver: None > PortContext.current['binding:host_id']: current value or None > PortContext.current['binding:vif_type']: 'unbound' > PortContext.bound_segment: None > PortContext.bound_driver: None > > 3c) In a port update operation on a previously bound port that does not > trigger unbinding or rebinding, all drivers' update_port_precommit() and > update_port_postcommit() methods will be called with PortContext > properties reflecting unchanged binding states as shown. > > PortContext.original['binding:host_id']: previous value > PortContext.original['binding:vif_type']: previous value > PortContext.original_bound_segment: previous value > PortContext.original_bound_driver: previous value > PortContext.current['binding:host_id']: previous value > PortContext.current['binding:vif_type']: previous value > PortContext.bound_segment: previous value > PortContext.bound_driver: previous value > > 3d) In a the port update operation on a previously bound port that does > trigger unbinding or rebinding, all drivers' update_port_precommit() and > update_port_postcommit() methods will be called with PortContext > properties reflecting the previously bound and currently unbound binding > states as shown. If a value for binding:host_id was supplied, binding > will occur afterwards as described in 4 below. > > PortContext.original['binding:host_id']: previous value > PortContext.original['binding:vif_type']: previous value > PortContext.original_bound_segment: previous value > PortContext.original_bound_driver: previous value > PortContext.current['binding:host_id']: new or current value > PortContext.current['binding:vif_type']: 'unbound' > PortContext.bound_segment: None > PortContext.bound_driver: None > > 4) If a port create or update operation triggers binding or rebinding, > it is attempted after the initial transaction is processed and committed > as described in 3 above. The binding process itself is just as before, > except it happens after and outside the transaction. Since binding now > occurs outside the transaction, its possible that multiple threads or > processes could concurrently attempt to bind the same port, although > this is should be a rare occurrence. Rather than trying to prevent this > with some sort of distributed lock or complicated state machine, > concurrent attempts to bind are allowed to proceed in parallel. When a > thread completes its attempt to bind (either successfully or > unsuccessfully) it then performs a second transaction to update the DB > with the result of its binding attempt. When doing so, it checks to see > if some other thread has already committed relevant changes to the port > between the two transactions. There are three possible cases: > > 4a) If the thread's binding attempt succeeded, and no other thread has > committed either a new binding or changes that invalidate this thread's > new binding between the two transactions, the thread commits its own > binding results, calling all drivers' update_port_precommit() and > update_port_postcommit() methods with PortContext properties reflecting > the new binding as shown. It then returns the updated port dictionary to > the caller. > > PortContext.original['binding:host_id']: previous value > PortContext.original['binding:vif_type']: 'unbound' > PortContext.original_bound_segment: None > PortContext.original_bound_driver: None > PortContext.current['binding:host_id']: previous value Are you not expecting/allowing the host_id to change in this scenario? Why? > PortContext.current['binding:vif_type']: new value > PortContext.bound_segment: new value > PortContext.bound_driver: new value > > 4b) If the thread's binding attempt either succeeded or failed, but some > other thread has committed a new successful binding between the two > transactions, the thread returns a port dictionary with attributes based > on the DB state from the new transaction, including the other thread's > binding and any other port state changes. No further calls to mechanism > drivers are needed here since they are the responsibility of the other > thread that bound the port. > > 4c) If some other thread committed changes to the port's > binding-relevant state but has not committed a successful binding, then > this thread attempts to bind again using that updated state, repeating 4. > > 5) Port deletion no longer does anything special to unbind the port. All > drivers' delete_port_precommit() and delete_port_postcommit() methods > are called with PortContext properties reflecting the binding state > before deletion as shown. > > PortContext.original: None > PortContext.original_bound_segment: None > PortContext.original_bound_driver: None > PortContext.current['binding:host_id']: previous value or None > PortContext.current['binding:vif_type']: previous value > PortContext.bound_segment: previous value > PortContext.bound_driver: previous value Could this part of the port deletion also be done by port update? > > 6) In order to ensure successful bindings are created and returned > whenever possible, the get port and get ports operations also attempt to > bind the port as in 4 above when binding:host_id is available but there > is no existing successful binding in the DB. > > 7) We can either eliminate MechanismDriver.unbind_port(), or call it on > the previously bound driver within the transaction in 3d and 5 above. If > we do keep it, the old binding state must be consistently reflected in > the PortContext as either current or original state, TBD. Since all > drivers see unbinding as a port update where current_bound_segment is > None and original_bound_segment is not None, calling unbind_port() seems > redundant. > > 8) If bindings shouldn't spontaneously become invalid, maybe we can > eliminate MechanismDriver.validate_bound_port(). > > > I've provided a lot of details, and the above may seem complicated. But > I think its actually much more consistent and predictable than the > current port binding code, and implementation should be straightforward. > > -Bob _______________________________________________ OpenStack-dev mailing list OpenStack-dev@lists.openstack.org http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
