Re: [netmod] [Teas] Key collision between configured and ephemeral list entries

["Rob Wilton (rwilton)" <[e-mail]>]

Hi Italo,

Using a prefix (which can also be configured by the user) for the system created objects to avoid name collisions seems reasonable to me.  I wouldn't use a symbol (like #), but instead would suggest a prefix string like "sys-".

But I think that it is appropriate to solve this within the specific data model rather that requiring a system wide solution.

Thanks,
Rob


> -----Original Message-----
> From: Italo Busi <[e-mail]>
> Sent: 19 June 2019 13:51
> To: Rob Wilton (rwilton) <[e-mail]>; Juergen Schoenwaelder
> <[e-mail]>
> Cc: [e-mail]; Tarek Saad <[e-mail]>; Andy Bierman
> <[e-mail]>; [e-mail]
> Subject: RE: [Teas] [netmod] Key collision between configured and
> ephemeral list entries
> 
> Hi Rob,
> 
> Thanks a lot for your comments
> 
> Your interpretation makes a lot of sense in case of an "intentional" name
> clash (e.g., when an entry is configured by the client in the <running> DS
> to configure some intended behavior, like admin status, for an entry
> injected by the system in the <operational> DS): in this case the same
> name/key value is used to indicate that the two DS entries are referring
> to the same entity
> 
> My concern is how to avoid "unintentional" name clashes (e.g., between an
> entry configured by the client in the <running> DS and another entry
> injected by the system in the <operational> DS) because in this situation
> the behavior described below is not desirable: the two DS entries are
> actually referring to two different entities which by accident got
> assigned the same name/key value
> 
> Italo
> 
> -----Original Message-----
> From: Rob Wilton (rwilton) [mailto:[e-mail]]
> Sent: mercoledì 19 giugno 2019 11:07
> To: Italo Busi <[e-mail]>; Juergen Schoenwaelder
> <[e-mail]>
> Cc: [e-mail]; Tarek Saad <[e-mail]>; Andy Bierman
> <[e-mail]>; [e-mail]
> Subject: RE: [Teas] [netmod] Key collision between configured and
> ephemeral list entries
> 
> Hi Italo,
> 
> My interpretation of the NMDA guidelines are thus:
> 
> - If multiple clients are writing the same values to <running> then the
> clients must coordinate between themselves to ensure that the correct
> values are written to <running>, otherwise the last verified change
> written to <running> wins.  Locks can be used to coordinate client writes
> to <running> if required.
> 
> - If multiple clients are writing to different datastores, e.g. one client
> is writing to <running> and another is writing to some form of ephemeral
> datastore, then the ephemeral datastore definition must specify what
> mechanism is used to resolve configuration conflicts between configuration
> datastores.  Naively, my starting point would be to say that configuration
> in an ephemeral datastore should override configuration that is in
> <running>.
> 
> - If the decision is from a data node configured in <running> and a data
> node injected by the system into <operational> then it is up to the device
> to decide how to resolve these (i.e. the system chooses which version of
> the data node to use, and the result of that decision is tagged in
> <operational> using the origin metadata).  Generally, I would expect an
> explicitly configured data node in <running> should take precedence over
> system generated config, but there might be cases where this doesn't make
> sense, and perhaps there might be cases where the data model recommends
> different behaviour.
> 
> - I would assume that there is only a single <operational> datastore.  I'm
> not sure whether NMDA explicitly requires this, but we couldn't think of
> any scenario where multiple operational datastores would be helpful.
> 
> Thanks,
> Rob
> 
> 
> > -----Original Message-----
> > From: Teas <[e-mail]> On Behalf Of Italo Busi
> > Sent: 18 June 2019 18:24
> > To: Juergen Schoenwaelder <[e-mail]>
> > Cc: [e-mail]; Tarek Saad <[e-mail]>; Andy Bierman
> > <[e-mail]>; [e-mail]
> > Subject: Re: [Teas] [netmod] Key collision between configured and
> > ephemeral list entries
> >
> > Hi Juergen,
> >
> > What is the DS architecture you have in mind with multiple client
> > creating entries?
> >
> > Are the two clients creating entries in the same <running> DS or in
> > two different <running> DS?
> >
> > In the latter case, the two clients could also rely on different
> > <operational> DS and therefore can assign the same name to different
> > entries (since they will be instantiated in different DS). There is no
> > need for them to avoid name clash
> >
> > In the former case, a name clash would cause one client to override
> > the configuration of another client
> >
> > Are the two clients aware of each other?
> >
> > I take the opportunity to clarify one point (not sure I have been
> > clear about it). I do not think we need to define any rule which is
> > enforced by the server to avoid name clashes since the server cannot
> > understand whether the name clash is intentional or not. I think we
> > just need to define some known/common/standard rules that allow the
> > client(s) to avoid creating unintended name clashes.
> >
> > Thanks, Italo
> >
> > -----Original Message-----
> > From: Juergen Schoenwaelder
> > [mailto:[e-mail]]
> > Sent: martedì 11 giugno 2019 20:37
> > To: Italo Busi <[e-mail]>
> > Cc: Andy Bierman <[e-mail]>; [e-mail]; Tarek Saad
> > <[e-mail]>; [e-mail]
> > Subject: Re: [netmod] [Teas] Key collision between configured and
> > ephemeral list entries
> >
> > On Tue, Jun 11, 2019 at 05:43:27PM +0000, Italo Busi wrote:
> >
> > > [Italo Busi] If the client knows the prefix used by the server, it
> > > can pick up a different prefix and use it to tag its own entries. I
> > > think this rule is not really complex and it seems much simpler than
> > > managing unintended name clashes
> >
> > A prefix only helps a little. Once you have multiple clients creating
> > entries, you will have to handle collisions again. Sometimes solving
> > the more general case leads to solutions that also work nicely in
> > simpler special cases.
> >
> > /js
> >
> > --
> > Juergen Schoenwaelder           Jacobs University Bremen gGmbH
> > Phone: [phone]         Campus Ring 1 | 28759 Bremen | Germany
> > Fax:   [phone]         <https://www.jacobs-university.de/>
> >
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