The keyword phrase here is “certain legacy applications.” Docker learned while developing MTA that when it comes to migrating to containers, not all legacy apps are created equally. Some can make the transition fairly easily, others not so much. The good news is that through its experimentation, Docker has come up with a checklist to predict how successfully an app can be containerized, and it’s so accurate that the company can guarantee a successful move within a specified time period, as well as the cost of the move, for applications that meet the criteria.