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

[Ludwig Krispenz]

On 05/28/2015 05:35 PM, Simo Sorce wrote:
> On Thu, 2015-05-28 at 17:18 +0200, Ludwig Krispenz wrote:
>> On 05/28/2015 05:03 PM, Martin Kosek wrote:
>>> On 05/28/2015 04:59 PM, Ludwig Krispenz wrote:
>>>> 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.
>>> Topology should not care about these settings at all, this is only for
>>> domainlevel API to validate if the level can be raised or not. Topology plugin
>>> should be only checking the effective Domain Level in cn=ipa,cn=etc,SUFFIX.
>> and then ? it reads domain level to be say 1, what is the trigger.
>> now I am confused, Simo say it should not compare it to the plugin
>> version, you say it should not compare to the server level,
>>
>> so what ? hard code on domain level 1?
> In the plugin you should have this variable as a global (for the plugin)
>
> int topology_min_domain_level = 1
>
> You *know* the plugin can activate only if domain_level is 1, it is ok
> to hard code it, once we release the code we will never change this.
> The plugin will be forever and ever enabled only if the global domain
> level you read from cn=ipa,cn=etc,SUFFIX is >= 1
this is ok, if we all agree
only this thread started suggesting that the plugin should only start 
when it is >= 2
and have level 1 for the DNS stuff - so, even if this wasn't valid, 
sometimes it could help to have a config value to compare to.

but I am fine with hard coding it in the plugin to 1
>
> It doesn't matter if in 2025 we are at topology plugin version 7.0 and
> the domain level supported are now 0 through 42, you will still enable
> the basic behavior at domain level >= 1
>
> Later on additional features may be conditional on other domain levels,
> and eventually we may even become incompatible with domain level 1 and
> require a higher level, but that will always be something you know
> statically in the code, you will never have a reason or a way to
> dynamically change domain level support within the plugin.
>
> Simo.
>