try making it as 2 apps, one for API only and one for UI, that way you can make changes independently and replace them with other technologies when needed. We h

try making it as 2 apps, one for API only and one for UI, that way you can make changes independently and replace them with other technologies when needed. We have build a few large applications this way. for api use rails-api and for web use any framework, you can use rails or if it is based on backbone.js or simple bootstrap, you can use sinatra for it. for scaling, identify the bottleneck and solve it. first bottleneck would be database, there are known solutions for it, cluster, sharding, read write seperations etc. do less per request, bring in a messaging queue to handle the parts. e.g.. incoming and outgoing email processing