What this, and other recent failures at other airlines, shows is a lack of professionalism in their IT departments.
More a lack of professionalism in the budgeting department.
Looks to me like their mainframe went down.
All tracking of Planes, Passengers, Baggage, Freight, Meals, Maintenance, Flight Planning and on and on and on will be down.
CIA, NSA, MIA, KGB, bla bla bla take a dim view of Flights leaving without prior notification of browsing history, credit card details and so on of each person on board.
Mainframes generally take many hours to get up and running again once the problem is identified and resolved. Many hundreds of subsystems need to be individually started in the right sequence and verified for proper operation.
You being unable to purchase a ticket is the last of anybody's worries.
Last outage I saw (other BIG player in Europe) cost more than €10 million, previous outage more then 14 years ago. Cost of parallel backup system: €40 million just to set up.
You do the math ....