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From "scott comer (sccomer)" <scco...@cisco.com>
Subject Re: naming service again...
Date Mon, 02 Feb 2009 17:42:33 GMT
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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