Add support to cancel/force rollback a migration

[danzika]

In managed environments, like AWS RDS or GCP CloudSQL it is necessary to run the migration from a separate machine.
Then a network issue, ec2/vm failure or similar can happen causing the db connections to drop, failing the migration in turn.
This is likely to leave the migration in an inconsistent state, being unable to neither complete nor rollback, having to cleanup manually.
Please, add option abort/cancel/force rollback that wouldn't stop on consistency errors on only partially completed migration.

[exekias]

Thank you for opening this @danzika, do you have some logs of the errors you saw that you can share? It would be interesting to see those to diagnose the issue.

I agree overall it should be possible to recover from a failed start, either with the rollback command or something else

[danzika]

Actually I don't have logs for this. We just discussed this feature yesterday on a Meetup with @tsg.
So this is rather a feature request/enhancement than actual bug I have hit :)

[exekias]

Nice! thank you for opening. I believe as of today it's already possible to rollback a failed start. We make rollback operations idempotent so they can be run against intermediate states of start. Let's keep the issue open to double check this before closing it!

[danzika]

Amazing! Thanks for instant reaction. If already implemented it brings the tool one step closer to production readiness. Kudos