I cannot say why Heroku sends TERM signals, but here's why I would do it if I were designing a a PaaS: * You want to instill the right culture in your customer

I cannot say why Heroku sends TERM signals, but here's why I would do it if I were designing a a PaaS: * You want to instill the right culture in your customers code, that everything can fail, often, and they have to build software with that in mind. That's because stuff will fail always, and your customers will have to handle failures anyway, otherwise they will blame you. * It's easier and cheaper to manage your fleet if all you have to care is that ninetysomething percent of your hosts are healthy. * You can also detect broken machines more easily if you can remove it from the cluster as soon as you suspect it, knowing that no customers will be hurt. Where "broken" can mean anything, sometimes some instances will just run slowly, have bad IO, slow network, whatever, you don't care, you know you can just kill and respawn the containers as long as the total number of dynos meets the requirements and you don't exceed some predetermined rate of churn, which would affect the customer. * You need to perform maintenance on machines where your run your customers containers/VMs. You can implement live migration, but it has a cost (implementation, management, storage etc), even more true a few years ago. * You need to perform maintenance within the customers containers themselves; live migration won't help you with that. You don't want to bother your customers with maintenance windows. * It's easy and cheap to "move" around containers across machines in order to balance load, spread an application across power domains.