Open Stack

On 19 January 2015 at 05:13, Angus Salkeld <asalkeld at mirantis.com> wrote:

> On Fri, Jan 16, 2015 at 11:10 PM, Sergey Kraynev <skraynev at mirantis.com>
> wrote:
>
>> Steve, Thanks for the feedback.
>>
>> On 16 January 2015 at 15:09, Steven Hardy <shardy at redhat.com> wrote:
>>
>>> On Thu, Dec 25, 2014 at 01:52:43PM +0400, Sergey Kraynev wrote:
>>> >    Hi all.
>>> >    In the last time we got on review several patches, which removes old
>>> >    deprecation properties [1],A
>>> >    and one mine [2].
>>> >    The aim is to delete deprecated code and redundant tests. It looks
>>> simple,
>>> >    but the main problem, which we met, is backward compatibility.
>>> >    F.e. user has created resource (FIP) with old property schema, i.e.
>>> using
>>> >    SUBNET_ID instead of SUBNET. On first look nothing bad will not
>>> happen,
>>> >    because:
>>>
>>> FWIW I think it's too soon to remove the Neutron subnet_id/network_id
>>> properties, they were only deprecated in Juno [1], and it's evident that
>>> users are still using them on icehouse [2]
>>>
>>> I thought the normal deprecation cycle was at least two releases, but I
>>> can't recall where I read that.  Considering the overhead of maintaining
>>> these is small, I'd favour leaning towards giving more time for users to
>>> update their templates, rather then breaking them via very aggresive
>>> removal of deprecated interfaces.
>>>
>>
>> Honestly I thought, that we use 1 release cycle, but I have not any
>> objections to do it after two releases.
>> Will  be glad to know what is desired deprecation period.
>>
>>
>>>
>>> I'd suggest some or all of the following:
>>>
>>> - Add a "planned for removal in $release" to the SupportStatus string
>>>   associated with the deprecation, so we can document the planned
>>> removal.
>>> - Wait for at least two releases between deprecation and removal, and
>>>   announce the interfaces which will be removed in the release notes for
>>>   the release before removal e.g:
>>>     - Deprecated in Juno
>>>     - Announce planned removal in Kilo release notes
>>>     - Remove in "J"
>>
>>
>> I like this idea, IMO it will make our deprecation process clear.
>>
>>
>>>
>>
>>
>>> [1] https://review.openstack.org/#/c/82853/
>>> [2]
>>> http://lists.openstack.org/pipermail/openstack/2015-January/011156.html
>>>
>>> >    1. handle_delete use resource_id and any changes in property schema
>>> does
>>> >    not affect other actions.
>>> >    2. If user want to use old template, he will get adequate error
>>> message,
>>> >    that this property is not presented in schema. After that he just
>>> should
>>> >    switch to new property and update stack using this new property.
>>> >    In the same time we have one big issues for shadow dependencies,
>>> which is
>>> >    actual for neutron resources. The simplest approach will not be
>>> worked
>>> >    [3], due to old properties was deleted from property_schema.
>>> >    Why is it bad ?
>>> >    - we will get again all bugs related with such dependencies.
>>> >    - how to make sure:A
>>> >    A  A  - create stack with old property (my template [4])
>>> >    A  A  - open horizon, and look on topology
>>> >    A  A  - download patch [2] and restart engine
>>> >    A  A  - reload horizon page with topology
>>> >    A  A  - as result it will be different
>>> >    A
>>> >    I have some ideas about how to solve this, but none of them is not
>>> enough
>>> >    good for me:
>>> >    A - getting such information from self.properties.data is bad,
>>> because we
>>> >    will skip all validations mentioned in properties.__getitem__
>>> >    A - renaming old key in data to new or creating copy with new key
>>> is not
>>> >    correct for me, because in this case we actually change properties
>>> >    (resource representation) invisibly from user.
>>> >    A - as possible we may leave old deprecated property and mark it
>>> something
>>> >    like (removed), which will have similar behavior such as for
>>> >    implemented=False. I do not like it, because it means, that we never
>>> >    remove this "support code", because wants to be compatible with old
>>> >    resources. (User may be not very lazy to do simple update or
>>> something
>>> >    else ...)
>>> >    - last way, which I have not tried yet, is usingA
>>> _stored_properties_data
>>> >    forA extraction necessary information.
>>> >    So now I have the questions:
>>> >    Should we support such case with backward compatibility?A
>>> >    If yes, how will be better to do it for us and user?
>>> >    May be we should create some strategy forA removingA A deprecated
>>> >    properties ?
>>>
>>> Yeah, other than the process issues I mentioned above, Angus has pointed
>>> out some technical challenges which may mean property removal breaks
>>> existing stacks.  IMHO this is something we *cannot* do - folks must be
>>> able to upgrade heat over multiple versions without breaking their
>>> stacks.
>>>
>>> As you say, delete may work, but it's likely several scenarios around
>>> update will break if the stored stack definition doesn't match the schema
>>> of the resource, and maintaining the internal references to removed or
>>> obsolete properties doesn't seem like a good plan long term.
>>>
>>> Could we provide some sort of migration tool, which re-writes the
>>> definition of existing stacks (via a special patch stack update maybe?)
>>> before upgrading heat?
>>>
>>
>> Yeah, I thought about it. Probably it's good solution for upgrading.
>> However one thing stops me to start doing it right now:
>> If we "upgrade"  old resources and stored templates we will come
>> to situation, when user's template and stored are different.
>> And in this case user's template looks like invalid and can not be used
>> without updating wrong properties.
>> If we deal with it, I look forward to make this solution work.
>>
>
> Can't we change the property definition to be a migration function?
> - It would not be visible to users (once deprecated)
> - On loading the template, it would run the migration function that could
>   do a migration.
>
> The question is it even possible to achieve technically? But it would be
> nice in
> that we could stay compatible for ever.
>
> -Angus
>
>
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>
Angus, I think, that it should be possibly.
Also your suggestion gave me a idea. We can roll up all old/deprecated
properties.
F.e. add option:

property_schema = {
    subnet:
      ....
      old_names (or something like that) = subnet_id
}

So during creation we will define two properties in template with the same
values.
IMO, it should work well, because all deprecated properties now is just
renamed properties.

Also, as you suggested above, we may migrate this "deprecation key" and say
user, that he should change his template.

Regards,
Sergey.
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