Open Stack

Dear OpenStack devs,

A recent review [1] dragged into spotlight how damaging improper use of
external code inside migrations can be.

Basically in my mind the incident raises 2 issues that I think we should
look into:

1) How can we make reviewing changes with db migrations more robust

Since we use sqlalchemy-migrate to version our database, the package's
documentation [2] states how care needs to be taken when importing code
inside a db migration script. It seems like this can be taken care of
with a hacking rule that will fail the patch if anything outside a
subset of modules is imported and used. I might be missing an angle
where such an approach could cause issues, so feel free to comment in
replies. IIUC - this is something we might want to enforce even when/if
we move to using Alembic for migrations.

2) What are acceptable changes

The patch also raised the question of what is acceptable level of
changes. The only guidelines I could find are [3] and they seem fuzzy
enough that we might want to be more specific, or introduce stricter
testing guidelines.

All comments are more than welcome,

Thanks,

Nikola

[1] https://review.openstack.org/#/c/39929/
[2]
https://sqlalchemy-migrate.readthedocs.org/en/v0.7.2/versioning.html#edit-the-change-script
[3] https://wiki.openstack.org/wiki/DbMigrationChangeGuidelines