On 18.4.2016 16:42, Martin Basti wrote:
> On 18.04.2016 15:22, Petr Spacek wrote:
>> On 6.4.2016 10:57, Petr Spacek wrote:
>>> On 6.4.2016 10:50, Jan Cholasta wrote:
>>>> On 4.4.2016 13:51, Petr Spacek wrote:
>>>>> 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.
>>>> If server can be only in one location, why bother with
>>>> location-{add,mod,remove}-member and not use server-mod:
>>>>      server-mod <FQDN> --location=<NAME> [--location-weight=0..65535]
>>>> ? This is the natural way to model one-to-many relationships in the API,
>>>> consistent with existing stuff.
>>> I originally wanted to have location-add-member command so (external) DNS
>>> servers and IPA servers can be assigned to a location using the same 
>>> command:
>>> location-add-member     LOCATION_NAME --ipa-server=<FQDN>
>>> location-add-member     LOCATION_NAME --advertising-server=<server/view ID>
>>> Should I split this between
>>> server-mod <FQDN> --location=<NAME> [--location-weight=0..65535]
>>> and
>>> dnsserver-mod <server/view ID> --type=external --advertise-location=...
>>> I do not like splitting server-to-location assignment management between two
>>> commands very much. Current proposal in design page was inspired by
>>> group-add-member command which has --users and --groups options which seemed
>>> philosophically similar to me.
>>> Anyway, I'm open to suggestions how to handle this.
>> Honza and me are playing with idea that Server Roles can be re-used for
>> Locations, too.
>> The rough idea is that 'the advertising' server will have a role like 'DNS
>> Location XYZ DNS server' and that the member server will have role like 'IPA
>> master in location XYZ'.
>> (Pick your own names, these are just examples.)
>> Obvious advantage is consistency in the user interface, which is something we
>> really need.
>> The question is how where to put equivalent of --weight option.
>> This would make location-add-member command unnecessary.
> Today I found out that I misunderstood how non-IPA SRV records will work with
> the DNS locations feature.
> I expected that other SRV record stored in IPA domain will be copied unchanged
> to locations, only for IPA services SRV records will be altered with 
> priorities.
> However, DNS locations *will not* handle other SRV than IPA ones, what
> effectively means that custom user SRV records will disappear on hosts thats
> belong to a location.

Yes, thank you for pointing this out explicitly.

I've tried to capture all I know about this to the design page:

Copy follows so we can discuss it quickly:

=== Interaction with hand-made records ===
Side-effect of DNAME-redirecting <tt>_udp</tt> and <tt>_tcp</tt> subdomains is
that all original names under these subdomains will become occluded/invisible
to clients (see [https://tools.ietf.org/html/rfc6672#section-2.4 RFC 6672
section 2.4]).

This effectively means that hand-made records in the IPA DNS domain will
become invisible. E.g. following record will disappear when DNS locations are
configured and enabled on IPA domain <tt>ipa.example</tt>:

 _userservice._udp.ipa.example.  SRV record: 0 100 123

This behavior is in fact necessary for seamless upgrade of replicas which do
not understand the new template LDAP entries in DNS tree. Old replicas will
ignore the template entries and use original sub-tree (and ignore
<tt>_locations</tt> sub-tree). New replicas will understand the entry,
generate DNAME records and thus occlude old names and use only new ones (in
<tt>_locations</tt> sub-tree).

Note: This would be unnecessary if IPA used standard DNS update protocol
against standard DNS server with non-replicated zones because we would not
need to play DNAME tricks. In that case we could instead update records on
each server separately. With current LDAP schema we cannot do that without
adding non-replicated part of LDAP tree to each DNS server.
* If we added non-replicated sub-tree to each IPA DNS server we would have
another set of problems because hand-made entries would not be replicated
among IPA servers.

Handling of hand-made records adds some interesting questions:
* How to find hand-made records?
** Blacklist on name-level or record-data level? What record fields should we
* How to handle collisions with IPA-generated records?
** Ignore hand-made records?
** Add hand-made records?
** Replace IPA generated ones with hand-made ones?
* What triggers hand-made record synchronization?
** Should the user or IPA framework call ''ipa dnslocation-fix-records'' after
each hand-made change to DNS records?
** How is this synchronization supposed to work with DNS update protocol?
Currently we do not have means to trigger an action when a records is changed
in LDAP.
* How it affects interaction with older IPA DNS servers (see above)?

There are several options:
{{clarify|reason=What to do with hand-made records?}}
* For first version, document that enabling DNS location will hide hand-made
records in IPA domain.
* Add non-replicated sub-trees for IPA records and somehow solve replication
of hand-made records.
** What is the proper granularity? Create 20 backends so we can filter on
* Do 'something' which prevents replication of IPA-generated DNS records among
servers while still using one LDAP suffix.
** With this in place we can mark IPA-generated records as non-replicable
while still replicating hand-made records as usual. (An object class like
<tt>idnsRecordDoNotReplicate</tt>?) This would mean that we can drop whole
<tt>_locations</tt> sub-tree and each server will hold only its own copy of
DNS records.
* Find, filter and copy hand-made records from main tree into the
<tt>_locations</tt> sub-trees. This means that every hand-made record needs to
be copied and synchronized N-times where N = number of IPA locations.

My favorite option for the first version is 'document that enabling DNS
location will hide hand-made records in IPA domain.'

The feature is disabled by default and needs additional configuration anyway
so simply upgrading should not break anything.

I'm eager to hear opinions and answers to questions above.

Petr^2 Spacek

> Example:
> domain: ipa.test
> server: server.ipa.test
> custom SRV record in IPA domain: _userservice._udp  SRV record: 0 100 123
> server.ipa.test.
> The record above will not be accessible from clients that connect to server
> with enabled locations. I think that users may have own services on IPA server
> with custom SRV records, and I don't consider this behavior as user-friendly
> and blocker for deployment of this feature.
> NACK to design from me. We should fix this.

Petr^2 Spacek

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