To answer the concerns raised in the comments: we are a real company and it took 2 weeks (while working on other features and bugfixes) to migrate to Docker. The plus is that now we have experience with the platform and we can streamline the process. Again: we are not using microservices or anything like that, simply Docker containers instead of EC2 instances, which makes life pretty damn easier (and cheaper).

And 25 and 75 are bogus numbers, what if we start running 10 instances?