Prevent keystone from serving requests when schema or data migrations are not up to date

[Dolph Mathews]

There are three scenarios during a rolling upgrade process where we could prevent operators from doing the "wrong thing" (doing things out of order):

1) Operators running code from the next release before `keystone-manage db_sync --expand` has been run: If you run the next release before --expand is run, then you'll surely end up with fatal query errors as columns and tables won't exist that the app thinks should exist.

2) (the scary one) Operators running code from the next release before `keystone-manage db_sync --migrate` has been run: If you run the next release before --migrate is run, then any number of different types of failures are possible due to unpopulated columns & tables, including a risk of data loss as the new release tries to update records that it perceives to be unpopulated, which might propagate to the legacy schema during UPDATE operations, for example.

3) Operators running code from the previous release after `keystone-manage db_sync --contract` has been run: As in case (1), this may result in fatal query errors, but also presents a risk of introducing data inconsistency, as the legacy schema might not have a "full understanding" of the new schema, as would be the case with additive schema changes. The legacy application would no longer have triggers to rely on, so consequences would mostly be dependent on the default values of columns, constraints, etc.

The second case worries me, as it's the most likely scenario where operators might not realize what's going on until it's too late.

To prevent all of these scenarios, I think the application should check at startup to ensure that the expand and data migration repositories both match a minimum value (specifically, the most recent migration in the application's respective repositories).

Doing the same sort of check at startup for the contract repo would be more difficult, as it'd be entirely dependent on when you last upgraded (whether it be last stable/* release or master at any point), so I'd like to leave that out of scope here.

[Steve Martinelli (stevemar)]

No patch yet, we're running out of time for patches going into RC, so removing rc-potential

[Lance Bragstad (lbragstad)]

This seems related to a conversation I was just having with Jesse about:

https://bugs.launchpad.net/keystone/+bug/1642212

[Morgan Fainberg (mdrnstm)]

This is in violation of the rolling upgrade plans. Marking as "wont fix"

[Morgan Fainberg (mdrnstm)]

My mistake on previous comment. This is more: Keystone will have massive errors due to not having the columns expected if db_sync is not run. I don't think preventing serving data explicitly is a needed feature.