[openstack-dev] [neutron] [ipam] Migration to pluggable IPAM

Neil Jerram Neil.Jerram at metaswitch.com
Wed Mar 30 16:18:27 UTC 2016

On 30/03/16 16:08, Pavel Bondar wrote:

> We are now in early Newton, so it is good time to discuss plan for
> pluggable ipam for this release cycle.
> Kevin Benton commented on review page for current migration to pluggable
> approach [1]:
>> IMO this cannot be optional. It's going to be a nightmare to try to
>> support two IPAM systems that people may have switched between at
>> various points in time. I would much rather go all-in on the upgrade
>> by making it automatic with alembic and removing the option to use the
>> legacy IPAM code completely.
>> I've already been bitten by testing the new IPAM code with the config
>> option and switching back which resulted in undeletable subnets. Now
>> we can always yell at anyone that changes the config option like I
>> did, but it takes a lot of energy to yell at users and they don't care
>> for it much. :)
>> Even ignoring the support issue, consider schema changes. This
>> migration script will have to be constantly updated to work with
>> whatever the current state of the schema is on both sets of ipam
>> tables. Without constant in-tree testing enforcing that, we are one
>> schema change away from this script breaking.
>> So let's bite the bullet and make this a normal contract migration.
>> Either the new ipam system is stable enough for us to commit to
>> supporting it and fix whatever bugs it may have, or we need to remove
>> it from the tree. Supporting both systems is unsustainable.
> This sound reasonable to me. It simplify support and testing (testing
> both implementations in gate with full coverage is not easy).
>  From user prospective there should be no visible changes between
> pluggable ipam and non-pluggable.
> And making switch early in release cycle gives us enough time to fix any
> bug we will find in pluggable implementation.
> Right now we have some open bugs for pluggable code [2], but they are
> still possible to fix.
> Does it make sense to you?

Yes!  Kill the non-pluggable code already.  Neutron desperately needs to 
have less and simpler code in any area where it can possibly get it.


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