How to migrate a modular Sinatra app to AWS Lambda

Question

I have a modular Sinatra app that runs fine under rackup, that is with a config.ru that has three 'use' statements and one run statement. I am trying to get my head around how to port the application to AWS lambda where API_gateway will provide web server services and just call my app.

I am using the recommended lambda.rb script from https://github.com/aws-samples/serverless-sinatra-sample/blob/master/lambda.rb as my entrypoint. What I don't get is how, in the AWS Lambda micro-clime, do I assemble the modules/layers of my application without rackup and config.ru?

I assume that my noob brain is just missing something really basic in spite of the fact that I have read every blog post, bit of Sinatra and Rack documentation I know of, and the great "Sinatra Up and Running" book. What am I missing?

barnard barnard · Accepted Answer · 2021-01-05T01:44:14

Upon re-reading the book, "Sinatra: Up and Running" again, it seems that there is a fairly elegant solution. If I set up my lambda.handler entrypoint to point to a simple Sinatra router, then it will be the router that composes the individual controllers into a 'system' which will handle all of my end points. the example from the book:

Example 4-32. Using Sinatra as router
require 'sinatra/base'

class Foo < Sinatra::Base
  get('/foo') { 'foo' }
end

class Bar < Sinatra::Base
  get('/bar') { 'bar' }
end

class Routes < Sinatra::Base
  get('/foo') { Foo.call(env) }
  get('/bar') { Bar.call(env) }
end

run Routes

Of course, in my case, I won't need the 'run Routes' line. I will just have my lambda.handler call Routes, as in Routes.call. This seems very doable!

How to migrate a modular Sinatra app to AWS Lambda

1 Answers