On migrations to production systems

Migrations on production systems is one of the most complex thing there is in the field of software because it requires all-in-one system administration, database administration, software development and quality management, each at a high level of skill. We generally delegate  a certain level of quality management to the customer (because they're most qualified in telling us what's wrong) but all the other aspects have to be dealt with, without the smallest mistake, otherwise you don't get a running system in the end.