This looks like a very nice concept, I've been exploring something similar but didn't get quite as far into the engines. What I've been doing is have 1 rails app that does the stuff rails is good at and have smaller Sinatra apps mount into the config.ru for the parts like APIs and the parts that handles web hooks from external services. It's not as clean as your solution though as there is still model sharing.
It's very tempting to do model sharing because it just makes things so easy but I can definitely see having to rewrite models when the time comes to scale out the parts of the app that is getting more hits. With your approach I wouldn't have to worry about that because it's modular from the start.
Would love to give this approach a try! Thx for the article.
We had a very similar path at TaskRabbit. As we made all those other Rails and/or sinatra and/or node apps, we ran into the issues noted in the "Versus Many Apps" section. Basically: testing, coordination, and deployment were an order of magnitude more complicated. We obviously are now at this engine situation.
It's very tempting to do model sharing because it just makes things so easy but I can definitely see having to rewrite models when the time comes to scale out the parts of the app that is getting more hits. With your approach I wouldn't have to worry about that because it's modular from the start.
Would love to give this approach a try! Thx for the article.