On 4.4.2016 13:39, Martin Basti wrote:
> 
> 
> On 31.03.2016 09:58, Petr Spacek wrote:
>> On 26.2.2016 15:37, Petr Spacek wrote:
>>> On 25.2.2016 16:46, Simo Sorce wrote:
>>>> On Thu, 2016-02-25 at 15:54 +0100, Petr Spacek wrote:
>>>>> On 25.2.2016 15:28, Simo Sorce wrote:
>>>>>> On Thu, 2016-02-25 at 14:45 +0100, Petr Spacek wrote:
>>>>>>> Variant C
>>>>>>> ---------
>>>>>>> An alternative is to be lazy and dumb. Maybe it would be enough for
>>>>>>> the first
>>>>>>> round ...
>>>>>>>
>>>>>>> We would retain
>>>>>>> [first step - no change from variant A]
>>>>>>> * create locations
>>>>>>> * assign 'main' (aka 'primary' aka 'home') servers to locations
>>>>>>> ++ specify weights for the 'main' servers in given location, i.e.
>>>>>>> manually
>>>>>>> input (server, weight) tuples
>>>>>>>
>>>>>>> Then, backups would be auto-generated set of all remaining servers
>>>>>>> from all
>>>>>>> other locations.
>>>>>>>
>>>>>>> Additional storage complexity: 0
>>>>>>>
>>>>>>> This covers the scenario "always prefer local servers and use remote
>>>>>>> only as
>>>>>>> fallback" easily. It does not cover any other scenario.
>>>>>>>
>>>>>>> This might be sufficient for the first run and would allow us to
>>>>>>> gather some
>>>>>>> feedback from the field.
>>>>>>>
>>>>>>> Now I'm inclined to this variant :-)
>>>>>> To be honest, this is all I always had in mind, for the first step.
>>>>>>
>>>>>> To recap:
>>>>>> - define a location with the list of servers (perhaps location is a
>>>>>> property of server objects so you can have only one location per server,
>>>>>> and if you remove the server it is automatically removed from the
>>>>>> location w/o additional work or referential integrity necessary), if
>>>>>> weight is not defined (default) then they all have the same weight.
>>>>> Agreed.
>>>>>
>>>>>
>>>>>> - Allow to specify backup locations in the location object, priorities
>>>>>> are calculated automatically and all backup locations have same weight.
>>>>> Hmm, weights have to be inherited form the original location in all
>>>>> cases. Did
>>>>> you mean that all backup locations have the same *priority*?
>>>> Yes, sorry.
>>>>
>>>>> Anyway, explicit configuration of backup locations is introducing API and
>>>>> schema for variant A and that is what I'm questioning above. It is hard to
>>>>> make it extensible so we do not have headache in future when somebody
>>>>> decides
>>>>> that more flexibility is needed OR that link-based approach is better.
>>>> I think no matter we do we'll need to allow admins to override backup
>>>> locations, in future if we can calculate them automatically admins will
>>>> simply not set any backup location explicitly (or set some special value
>>>> like "autogenerate" and the system will do it for them.
>>>>
>>>> Forcing admins to mentally calculate weights to force the system to
>>>> autogenerate the configuration they want would be a bad experience, I
>>>> personally would find it very annoying.
>>>>
>>>>> In other words, for doing what you propose above we would have to design
>>>>> complete schema and API for variant A anyway to make sure we do not lock
>>>>> ourselves, so we are not getting any saving by doing so.
>>>> A seemed much more complicated to me, as you wanted to define a ful
>>>> matrix for weights of servers when they are served as backups and all
>>>> that.
>>>>
>>>>>> - Define a *default* location, which is the backup for any other
>>>>>> location but always with lower priority to any other explicitly defined
>>>>>> backup locations.
>>>>> I would rather *always* use the default location as backup for all other
>>>>> locations. It does not require any API or schema (as it equals to "all
>>>>> servers" except "servers in this location" which can be easily calculated
>>>>> on fly).
>>>> We can start with this, but it works well only in a stellar topology
>>>> where you have a central location all other location connect to.
>>>> As soon as you have a super-stellar topology where you have hub location
>>>> to which regional locations connect to, then this is wasteful.
>>>>
>>>>> This can be later on extended in whatever direction we want without any
>>>>> upgrade/migration problem.
>>>>>
>>>>> More importantly, all the schema and API will be common for all other
>>>>> variants
>>>>> anyway so we can start doing so and see how much time is left when it is
>>>>> done.
>>>> I am ok with this for the first step.
>>>> After all location is mostly about the "normal" case where clients want
>>>> to reach the local servers, the backup part is only an additional
>>>> feature we can keep simple for now. It's a degraded mode of operation
>>>> anyway so it is probably ok to have just one default backup location as
>>>> a starting point.
>>> Okay, now we are in agreement. I will think about minimal schema and API 
>>> over
>>> the weekend.
>> Well, it took longer than one weekend.
>>
>> There was couple of changes in the design document:
>> * ‎Feature Management: CLI proposal
>> * ‎Feature Management: web UI - idea with topology graph replaced original
>> complicated table
>> * Feature Management: described necessary configuration outside of IPA DNS
>> * Version 1 parts which were moved into separate document:
>> V4/DNS_Location_Mechanism_with_per_client_override
>> * ‎Assumptions: removed misleading reference to DHCP, clarified role of DNS
>> views
>> * Assumptions: removed misleading mention of 'different networks' and added
>> summary explaining how Location is defined
>> * Implementation: high-level outline added
>>
>> Current version:
>> http://www.freeipa.org/page/V4/DNS_Location_Mechanism
>>
>> Full diff:
>> http://www.freeipa.org/index.php?title=V4%2FDNS_Location_Mechanism&diff=12603&oldid=12514
>>
>>
>> Practical usage is described in section How to test:
>> http://www.freeipa.org/page/V4/DNS_Location_Mechanism#How_to_Test
>>
>>
>> I will think about LDAP schema after we agree on CLI.
>>
>> Petr^2 Spacek
>>
>>
>>> Petr^2 Spacek
>>>
>>>
>>>>>> - Weights for backup location servers are the same as the weight defined
>>>>>> within the backup location itself, so no additional weights are defined
>>>>>> for backups.
>>>>> Yes, that was somehow implied in the variant A. Sorry for not mentioning 
>>>>> it.
>>>>> Weight is always relative number for servers inside one location.
>>>> Ok it looked a lot more complex from your description.
>>>>
>>>> Simo.
> 
> Design review:
> 
> 1)
> You missed warning when there is no backup DNS server in location

Thanks, added.


> 2)
> "Number of IPA DNS servers <= number of configured IPA locations" I dont
> understand
> 
> You need at least one DNS server per location, thus  DNS servers >= locations

Good catch, fixed.


> 3)
> Design (Version 1: DNAME per client)  Link to design doesn't work for me

Oh, my wiki-fu was weak. Fixed.


> CLI looks good to me. Maybe we should explicitly write in design that
> priorities of the SRV records will be set statically (What values? 0 - servers
> in location, 100 - backup?)

I've added a note about static priorities. Particular values are just an
implementation detail so I would not clutter feature management section with 
that.

-- 
Petr^2 Spacek

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