There are many bad things which can happen during the infrastructure upgrade. Sometimes it is caused by a sysadmin mistake, sometimes it may be a software bug, but it really does not matter what the main reason is. You must fix it. Nowadays we have much easier job than – for instance – twenty years ago. Now we have Google, lots of blogs and other pages with millions of information. However, we should follow the way created on our own. Take a look on this scenario: