Rolling upgrades: online schema migration

[Grzegorz Grasza]

Future incompatible changes in sqlalchemy migrations, like removing, renaming columns and tables can break rolling upgrades (upgrades when multiple Keystone instances are run at different versions).

To address this, we can ban schema changes which cause incompatibilities, specifically drops and alters, like in Nova:

https://github.com/openstack/nova/blob/stable/liberty/nova/tests/unit/db/test_migrations.py#L224-L225

[Grzegorz Grasza (xek)]

I will be rebasing this against the "Move extensions to core" work

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/241603

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/241603
Committed: https://git.openstack.org/cgit/openstack/keystone/commit/?id=8234b92e5751c22e39d38eb4628c54c9b86d13de
Submitter: Jenkins
Branch: master

commit 8234b92e5751c22e39d38eb4628c54c9b86d13de
Author: Grzegorz Grasza <email address hidden>
Date: Wed Nov 4 14:41:53 2015 +0100

    Unit test for checking cross-version migrations compatibility

    Future incompatible changes in database schema, like removing,
    renaming columns and tables can break rolling upgrades (upgrades when
    Keystone services are run at different versions simultaneously). This
    patch bans schema changes which cause incompatibilities - specifically
    drops and alters. Note that it is not bullet-proof - some incompatible
    schema changes like adding incompatible constraints may still get through.

    Closes-Bug: #1509944
    Partially-Implements: bp online-schema-migration
    Change-Id: I080cba842adfd0be5d14a51a5ada1ae2ea62863b

[Thierry Carrez (ttx)]

This issue was fixed in the openstack/keystone 9.0.0.0b3 development milestone.