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From James Dixson <dixs...@gmail.com>
Subject Re: naming service again...
Date Mon, 02 Feb 2009 18:12:20 GMT
I think in my mind I was thinking in terms of a very simple
policy/default-preference role in NameService, vs. a specific syntax.
The idea being that the minimum request of the NS should be for 'api'
and then everything else is essentially a query for a specific
instance of that api.

The URI

    etch:api   - any instance or scheme is acceptable

would defer to the nameserver the responsibility to selecting in
instance and scheme for the api. Whereas as URIs like

    Exactly 'foo' instance of 'api' using 'tcp' scheme
        etch:api/foo/tcp

    Exactly 'foo' instance of 'api', prefer 'tls' but will accept 'tcp'
        etch:api/foo/tls,tcp
        etch:api/foo/tls?altname=api/foo/tcp
        etch:api/foo?scheme=tls,tcp

    Any instance of 'api', but only accept 'tls' scheme
        etch:api?scheme=tls

constrains the nameserver response based on the preferences of the client.

I am not advocating policy enforcement etc, just trying to draw the
demarcation between the minimum request to the ns and then a
convention for a standard set of query params.



--
james


On Mon, Feb 2, 2009 at 11:42 AM, scott comer (sccomer)
<sccomer@cisco.com> wrote:
> agreed, there is a distinction between the format of a name and it's
> significance to the
> name server and how the api might use it. in fact, the name is just a
> string, it can have
> whatever significance we want. but when you specify a certain name, it has
> significance
> only to the target name service and none other.
>
> still, for compatibility between name services and to avoid confusion
> between users
> it seems like we ought to narrow it down slightly.
>
> i was thinking about the significance of scheme on the way in. i might
> reasonably have
> two schemes based on tls, one with different filters, for example. i think
> the scheme
> perhaps doesn't need to be one to one with an actual scheme, but perhaps
> just a
> qualifier on instance name.
>
> so let's suppose this format (though you could use any format that your ns
> supports):
>
> api[/inst[/qual]]
>
> where inst count be inst1[,inst2...]
>
> and qual could be qual1[,qual2...]
>
> in either case, what we are suggesting here is again the notion of search.
> shouldn't this
> be better specified some other way?
>
> consider this:
>
> api/foo,bar/tls,tcp
>
> it is a nice compact way to express this:
>
> api/foo/tls
> api/foo/tcp
> api/bar/tls
> api/bar/tcp
>
> though that is somewhat ambiguous. you might prefer this order:
>
> api/foo/tls
> api/bar/tls
> api/foo/tcp
> api/bar/tcp
>
> what might work better would be this:
>
> etch:api/foo/tls?altname=api/bar/tls,api/foo/tcp,api/bar/tcp
>
> this eliminates the idea that a name might have wildcarding, while still
> allowing for the
> idea of an alternate address. this already mirrors something i'd like to see
> with tcp
> scheme:
>
> tcp://foo:8090?alt=bar:8090
>
> how do you interpret this:
>
> etch://ns1:8090/api/foo/tls?altname=api/bar/tls,api/foo/tcp,api/bar/tcp?alt=ns2:8090
>
> contact ns1 to translate the names, if ns1 offline use ns2. hmmm. what
> scheme should
> we use for contacting the ns?
>
> how about this:
>
> etch:api/foo/tls?altname=api/bar/tls,api/foo/tcp,api/bar/tcp?ns=tcp://ns1:8090,tcp://ns2:8090
>
> scott out
>
> James Dixson wrote:
>>
>> What if I do not know/care about the instance name or connection
>> scheme at runtime. The URI:
>>
>>    etch://<name_service_ip:port>/<api>/<instance>/<scheme>
>>
>> Both the <instance> and <scheme> path elements seem as if they should
>> be both optional and, as suggested by 'tcp,tls", tuples. So a service
>> URI could be as simple as:
>>
>>    etch:<api>  (or maybe also etch:///<api> )  --
>>             etch:///etch.examples.perf.Perf
>>             etch:etch.examples.perf.Perf
>>
>>    etch:<api>/<instance> --
>>             etch:etch.examples.perf.Perf/foo
>>             etch.etch.examples.perf.Perf/foo,bar
>>
>>    etch:<api>/<instance>/<scheme> --
>>             etch:etch.examples.perf.Perf/foo/tcp
>>             etch:etch.examples.perf.Perf/foo,bar/tcp
>>             etch:etch.examples.perf.Perf/foo/tcp,tls
>>             etch:etch.examples.perf.Perf/foo,bar/tcp,tls
>>
>>
>>
>> --
>> james
>>
>>
>>
>> On Mon, Feb 2, 2009 at 8:52 AM, scott comer <sccomer@cisco.com> wrote:
>>
>>>
>>> it was pointed out to me by james that the name service was a bit
>>> confused
>>> in its roll by mixing up the idea of
>>> name translation with the ideas of failover, replication, clustering, and
>>> grouping of services. while those ideas
>>> are important in a distributed system, they deserve their own specific
>>> treatment and should not be part of the
>>> name service itself. (replication of name servers itself is needed, but
>>> subject to a different discussion.)
>>>
>>> manoj and i reviewed the proposal for name service and struck the
>>> requirements that were specifically not
>>> related to implementing a basic name service. while replication of a name
>>> service is still important, and
>>> ought to be present, we feel we could make a good first cut without the
>>> specific requirement and then see
>>> where we can go.
>>>
>>> so we adjusted the proposal and fiddled the wording a bit to account for
>>> the
>>> shift in focus:
>>>
>>> http://cwiki.apache.org/ETCH/etch-name-service.html
>>>
>>> here are the important design principles as we see them:
>>>
>>> 1) a service or application should not have be overtly aware of the name
>>> service. it should be possible to
>>> deploy a service or application with or without the name service, with no
>>> conditional code or changes
>>> to code. thus use of a name service is purely a deployment consideration
>>> and
>>> is not required.
>>>
>>> 2) the name service should be supportable in a variety of styles or modes
>>> without changing the
>>> fundamental functional interface. indeed, the basic contract should be
>>> very
>>> simple.
>>>
>>> we've not updated the ns.etch file to match yet. probably today.
>>>
>>> thoughts? ideas? over the next few days manoj and i will publish some
>>> call
>>> flows and code snips to
>>> illustrate these ideas.
>>>
>>> scott out
>>>
>>>
>>>
>>>
>

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