> From: John Garbutt [mailto:j...@johngarbutt.com] > Sent: November 24, 2015 16:09 > On 24 November 2015 at 15:00, Balázs Gibizer <balazs.gibi...@ericsson.com> > wrote: > >> From: Andrew Laski [mailto:and...@lascii.com] > >> Sent: November 24, 2015 15:35 > >> On 11/24/15 at 10:26am, Balázs Gibizer wrote: > >> >> From: Ryan Rossiter [mailto:rlros...@linux.vnet.ibm.com] > >> >> Sent: November 23, 2015 22:33 > >> >> On 11/23/2015 2:23 PM, Andrew Laski wrote: > >> >> > On 11/23/15 at 04:43pm, Balázs Gibizer wrote: > >> >> >>> From: Andrew Laski [mailto:and...@lascii.com] > >> >> >>> Sent: November 23, 2015 17:03 > >> >> >>> > >> >> >>> On 11/23/15 at 08:54am, Ryan Rossiter wrote: > >> >> >>> > > >> >> >>> > > >> >> >>> >On 11/23/2015 5:33 AM, John Garbutt wrote: > >> >> >>> >>On 20 November 2015 at 09:37, Balázs Gibizer > >> >> >>> >><balazs.gibi...@ericsson.com> wrote: > >> >> >>> >>><snip> > >> >> >>> >>><snip> > >> >> >> >> > >> >> >>> >>There is a bit I am conflicted/worried about, and thats when > >> >> >>> >>we start including verbatim, DB objects into the > >> >> >>> >>notifications. At least you can now quickly detect if that > >> >> >>> >>blob is something compatible with your current parsing code. > >> >> >>> >>My preference is really to keep the Notifications as a > >> >> >>> >>totally separate object tree, but I am sure there are many > >> >> >>> >>cases where that ends up being seemingly stupid duplicate > >> >> >>> >>work. I am not expressing this well in text form :( > >> >> >>> >Are you saying we don't want to be willy-nilly tossing DB > >> >> >>> >objects across the wire? Yeah that was part of the > >> >> >>> >rug-pulling of just having the payload contain an object. > >> >> >>> >We're automatically tossing everything with the object then, > >> >> >>> >whether or not some of that was supposed to be a secret. We > >> >> >>> >could add some sort of property to the field like > >> >> >>> >dont_put_me_on_the_wire=True (or I guess a > >> >> >>> >notification_ready() function that helps an object sanitize > >> >> >>> >itself?) that the notifications will look at to know if it > >> >> >>> >puts that on the wire-serialized dict, but that's adding a > >> >> >>> >lot more complexity and work to a pile that's already growing > rapidly. > >> >> >>> > >> >> >>> I don't want to be tossing db objects across the wire. But I > >> >> >>> also am not convinced that we should be tossing the current > >> >> >>> objects over the wire either. > >> >> >>> You make the point that there may be things in the object that > >> >> >>> shouldn't be exposed, and I think object version bumps is > >> >> >>> another thing to watch out for. > >> >> >>> So far the only object that has been bumped is Instance but in > >> >> >>> doing so no notifications needed to change. I think if we > >> >> >>> just put objects into notifications we're coupling the > >> >> >>> notification versions to db or RPC changes unnecessarily. > >> >> >>> Some times they'll move together but other times, like moving > >> >> >>> flavor into instance_extra, there's no reason to bump > notifications. > >> >> >> > >> >> >> > >> >> >> Sanitizing existing versioned objects before putting them to > >> >> >> the wire is not hard to do. > >> >> >> You can see an example of doing it in > >> >> >> https://review.openstack.org/#/c/245678/8/nova/objects/service. > >> >> >> py, > >> >> >> cm > >> >> >> L382. > >> >> >> We don't need extra effort to take care of minor version bumps > >> >> >> because that does not break a well written consumer. We do have > >> >> >> to take care of the major version bumps but that is a rare > >> >> >> event and therefore can be handled one by one in a way John > >> >> >> suggested, by keep sending the previous major version for a while > too. > >> >> > > >> >> > That review is doing much of what I was suggesting. There is a > >> >> > separate notification and payload object. The issue I have is > >> >> > that within the ServiceStatusPayload the raw Service object and > >> >> > version is being dumped, with the filter you point out. But I > >> >> > don't think that consumers really care about tracking Service > >> >> > object versions and dealing with compatibility there, it would > >> >> > be easier for them to track the ServiceStatusPayload version > >> >> > which can remain relatively stable even if Service is changing to > >> >> > adapt > to db/RPC changes. > >> >> Not only do they not really care about tracking the Service object > >> >> versions, they probably also don't care about what's in that filter > >> >> list. > >> >> > >> >> But I think you're getting on the right track as to where this > >> >> needs to go. We can integrate the filtering into the versioning of the > payload. > >> >> But instead of a blacklist, we turn the filter into a white list. > >> >> If the underlying object adds a new field that we don't want/care > >> >> if people know about, the payload version doesn't have to change. > >> >> But if we add something (or if we're changing the existing fields) > >> >> that we want to expose, we then assert that we need to update the > >> >> version of the payload, so the consumer can look at the payload > >> >> and say "oh, in 1.x, now I get _______" and can add the appropriate > checks/compat. > >> >> Granted with this you can get into rebase nightmares ([1] still > >> >> haunts me in my sleep), but I don't see us frantically changing > >> >> the exposed fields all too often. This way gives us some form of > >> >> pseudo-pinning of the subobject. Heck, in this method, we could > >> >> even pass the whitelist on the wire right? That way we tell the > >> >> consumer > >> explicitly what's available to them (kinda like a fake schema). > >> > > >> >I think see your point, and it seems like a good way forward. Let's > >> >turn the black list to a white list. Now I'm thinking about creating > >> >a new Field type something like WhiteListedObjectField which get a > >> >type name (as the ObjectField) but also get a white_list that > >> >describes which > >> fields needs to be used from the original type. > >> >Then this new field serializes only the white listed fields from the > >> >original type and only forces a version bump on the parent object if > >> >one of the white_listed field changed or a new field added to the > >> white_list. > >> >What it does not solve out of the box is the transitive dependency. > >> >If today we Have an o.vo object having a filed to another o.vo > >> >object and we want to put the first object into a notification > >> >payload but want to white_list fields from the second o.vo then our > >> >white list needs to be able to handle not just first level fields > >> >but subfields too. I guess this is doable but I'm wondering if we > >> >can avoid inventing a syntax > >> expressing something like 'field.subfield.subsubfield' > >> >in the white list. > >> > >> Rather than a whitelist/blacklist why not just define the schema of > >> the notification within the notification object and then have the > >> object code handle pulling the appropriate fields, converting formats > >> if necessary, from contained objects. Something like: > >> > >> class ServicePayloadObject(NovaObject): > >> SCHEMA = {'host': ('service', 'host'), > >> 'binary': ('service', 'binary'), > >> 'compute_node_foo': ('compute_node', 'foo'), > >> } > >> > >> fields = { > >> 'service': fields.ObjectField('Service'), > >> 'compute_node': fields.ObjectField('ComputeNode'), > >> } > >> > >> def populate_schema(self): > >> self.compute_node = self.service.compute_node > >> notification = {} > >> for key, (obj, field) in schema.iteritems(): > >> notification[key] = getattr(getattr(self, obj), field) > >> > >> Then object changes have no effect on the notifications unless > >> there's a major version bump in which case a SCHEMA_VNEXT could be > >> defined if necessary. > > > > Nice idea I will try it. Thanks! It is seems to avoid the sub object > > field white lists problem as the needed notification field can always be > pulled directly from an object field. > > +1 > This is my preference, specific notification objects that are independently > versioned. > It feels like time saving to re-use existing objects, but it breaks the > interface > really.
I implemented the suggestion [1], it seems to work with basic tests [2] but there are some technicalities in the _populate_schema() you might want to check and comment. There will be notification sub-team meeting today [3] where we can discuss the idea further. Cheers, Gibi [1] https://review.openstack.org/#/c/247024/6/nova/objects/notification.py,cm [2] https://review.openstack.org/#/c/247024/6/nova/tests/unit/objects/test_notification.py,cm [3] https://wiki.openstack.org/wiki/Meetings/NovaNotification > > Thanks, > johnthetubaguy > > __________________________________________________________ > ________________ > OpenStack Development Mailing List (not for usage questions) > Unsubscribe: OpenStack-dev- > requ...@lists.openstack.org?subject:unsubscribe > http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev __________________________________________________________________________ OpenStack Development Mailing List (not for usage questions) Unsubscribe: openstack-dev-requ...@lists.openstack.org?subject:unsubscribe http://lists.openstack.org/cgi-bin/mailman/listinfo/openstack-dev
