[Freeipa-devel] Domain level for topology plugin = 2

[Ludwig Krispenz]

On 05/28/2015 04:46 PM, Simo Sorce wrote:
> On Thu, 2015-05-28 at 15:54 +0200, Ludwig Krispenz wrote:
>> On 05/28/2015 03:26 PM, Simo Sorce wrote:
>>> On Thu, 2015-05-28 at 14:11 +0200, Petr Spacek wrote:
>>>> On 28.5.2015 10:49, Martin Kosek wrote:
>>>>> On 05/28/2015 09:05 AM, Petr Spacek wrote:
>>>>>> On 28.5.2015 08:55, Jan Cholasta wrote:
>>>>>>> Dne 26.5.2015 v 16:32 Petr Spacek napsal(a):
>>>>>>>> On 26.5.2015 16:16, Martin Kosek wrote:
>>>>>>>>> On 05/26/2015 04:13 PM, thierry bordaz wrote:
>>>>>>>>>> On 05/26/2015 02:12 PM, Petr Spacek wrote:
>>>>>>>>>>> Hello,
>>>>>>>>>>>
>>>>>>>>>>> it came to my mind that domain level for topology plugin should actually be
>>>>>>>>>>> number 2, not 1.
>>>>>>>>>>>
>>>>>>>>>>> We already used number 1 for incompatible changes in DNS tree and I believe
>>>>>>>>>>> that it is not a good idea to have two places which say 'version 1' but and
>>>>>>>>>>> actually mean two different things. (DNS tree version 1 + domain level 1)
>>>>>>>>>>>
>>>>>>>>>>> Patch is attached.
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>> Hello,
>>>>>>>>>> The fix looks good but that seems strange to have to set the initial
>>>>>>>>>> version of
>>>>>>>>>> the topology plugin to 2.0. (IIUC That is the version that will be written in
>>>>>>>>>> dse.ldif)
>>>>>>>>>> I would rather expects that topology plugin 1.0, would activate itself if the
>>>>>>>>>> DomainLevel is 2.0 or more.
>>>>>>>>>> If topology plugin 1.0 sets an internal DomainLevel_trigger=2.0 then activate
>>>>>>>>>> itself if DomainLevel >= DomainLevel_trigger.
>>>>>>>>>>
>>>>>>>>>> Let's wait for Ludwig feedback.
>>>>>>>>>>
>>>>>>>>>> thanks
>>>>>>>>>> thierry
>>>>>>>>> My personal opinion on this is to start with Domain Level 1 regardless. We
>>>>>>>>> already "solved" the DNS forwarders otherwise, with docs, async updates etc. I
>>>>>>>>> do not think we will be returning to implementing proper Domain Level support
>>>>>>>>> for that anyway.
>>>>>>>>>
>>>>>>>>> So I rather think that all the "Domain Level starts with 0, 1 is unused, 2 is
>>>>>>>>> the top one" will cause unforeseen issues I would rather like to avoid.
>>>>>>>> I'm more worried about confusion in future. To to me it simply seems easier to
>>>>>>>> bump one integer now than to document and explain (to users & new developers)
>>>>>>>> why we have two "ones" which mean something else.
>>>>>>>>
>>>>>>>> Code-wise it is just an integer.
>>>>>>>>
>>>>>>>> Also, it can simplify logic in future when we decide to do another
>>>>>>>> incompatible change in DNS tree because we will have only one integer to test
>>>>>>>> (instead of checking two separate version attribute in DNS tree & domain
>>>>>>>> level).
>>>>>>> +1, but I think the minimum supported domain level should be 1, not 0, because
>>>>>>> 0 means the server uses the old DNS schema, which we do not support anymore,
>>>>>>> right?
>>>>>> Good point!
>>>>>>
>>>>> It may be a good point, but it does not make the situation easier. You still
>>>>> have RHEL/CentOS 6.x IPA out there, where some of them already support the new
>>>>> DNS forwarders and some don't - and neither of them support Domain Levels -
>>>>> i.e. have Domain Level 0.
>>>>>
>>>>> As I said, I still see more complications with this proposals than benefits...
>>>> I would argue that it actually helps.
>>>>
>>>> If domain level = 1 then we can be *sure* that all replicas support the new
>>>> DNS semantics.
>>>>
>>>> If domain level = 0 then we know nothing (because of patched RHEL 6) and it is
>>>> a warning sign for diagnostic tools and also us when it comes to debugging.
>>> First of all  a domain level is something we change *RARELY*, and it is
>>> a whole number and it is an all or nothing thing.
>>>
>>> I do not understand why plugin versions matter at all, plugin version
>>> have nothing to do with domain levels. Each plugin *whatever* the
>>> version MUST always support at least 2 levels, because every domain you
>>> have will have to go through a domain_level transition when a new domain
>>> level comes out.
>>>
>>> Finally no single developer should be allowed to decide on  anew domain
>>> level, this must be a well ponder team decision as all plugins that need
>>> to change behavior based on domain level will be affected so a thorough
>>> review of what changes are needed across all plugins must be done every
>>> time someone propose a change that requires a domain level bump.
>>>
>>> Last but not least we should consider domain levels as something that
>>> changes *very* slowly, because otherwise you'll have to support many
>>> domain levels within any plugins that have to change behavior according
>>> to the domain level.
>>> I would say that the domain level should not change more frequently than
>>> once a year or so. It would be too much code churn to do otherwise.
>>>
>>> So for now domain_level should be set to 0. And the topology plugin will
>>> be enabled only when we turn it to 1. However we shouldn't turn it to 1
>>> until we have the replica promotion code at least, because only then we
>>> can make full use of the topology plugins.
>>>
>>> The DNS mess is unfixable, unless Petr you volunteer to backport code to
>>> change the behavior of the DNS based on the domain level, if that's the
>>> case then you can tie old behavior to level 0 and new behavior to level
>>>> = 1, but I do not think you want to do that given we already have
>>> "level 0" servers that sport the new code and changed the data in the
>>> directory, so let's just ignore DNS for the purpose of this discussion,
>>> except for nothing that once we finally switch to level 1 then all
>>> servers must be running with the newer DNS schema and older is not
>>> supported.
>>>
>>> Ah, I almost forgot, there is no "domain level for XYZ plugin", the
>>> domain level is one for the whole server, I want to make it very clear,
>>> because the title and part of the discussion seem to imply that you have
>>> per-plugin domain levels. If anything like that actually exist in the
>>> topology plugin code it must be ripped out now, plugin version and
>>> domain level are completely disjointed things and no correlation should
>>> or can exist, the only thing that can exist is whether the server, as a
>>> whole, supports a specific domain level or not.
>>>
>>> So once we decide domain level X comes to existence we basically freeze
>>> what it means and any new development that may require a domain level
>>> bump risk being delayed until we are ready for a new domain level bump,
>>> which should not happen very often.
>>>
>>> So let's make it very clear what level 1 means because the next release
>>> will then support only 0 and 1, and once a new version will come out
>>> with support for "level 2" we want be able to use any of the features
>>> tied to level 2 until all servers in the next release have been
>>> upgraded, and that may be a years long process, so we can't just churn
>>> domain level numbers as we need to support working on older levels for
>>> extended periods.
>> Hi Simo,
>>
>> you say the topology plugin should only activate itself if the domain
>> level is >= 1, at the moment this is done
>> by checking if plugin_version (1.0) >= domain_level (1).
> I do not understand what this means
>
>> If you want a different method/fields for decision, how do you want it
>> handled ?
> I do not see why you need to check for the topology plugin version, what
> you need is a "min_domain_level" version for now and just check:
> if domain_level >= min_domain_level:
>     do stuff
but right now installation sets
ipaMinDomainLevel: 0
ipaMaxDomainLevel: 1

in the master entry, so we would always do stuff.
>
> In the future we may grow more complex requirements and activate 'parts'
> of the plugin based on the domain level, so you could have something
> like:
>
> if domain_level >= min_domain_level:
>     do basic stuff
>     if domain_level >= feature_X_min_domain_level:
>         enable feature X
>
>
> So a general topology plugin version is not really interesting, the code
> above may still be there in version 5.0 of the topology plugin.
> We need a general minimum domain level version and then in future
> per-feature minimum domain level checks.
>
> Simo.
>
>