They run on Heroku using puma
We run on Heroku using Puma because several years ago I was pulling my hair out trying to get my Rails server working and found Heroku and got everything set up in about ten minutes.
Haven't looked back since. Others in the industry have caught up to Heroku in this regard, so I can't say I'm hooked for life, but I've defaulted to them ever since. So when this was a solo project I just went with what I knew.
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