Serverless config with function support. https://github.com/DavidWells/configorama#usage

serverless-config.yml

service: my-service

custom:
  one: 'hello'
  two: 'there'
  together: ${merge(${custom.one}, ${custom.two})}
  # ^ resolves to 'hellothere'

provider:
  name: aws
  runtime: nodejs8.10

functions:
  currentTime:
    handler: handler.endpoint
    events:
      - http:
          path: ping
          method: get

serverless.js

/* Serverless framework reads this file */
const path = require('path')
const configorama = require('configorama')
const cliFlags = require('minimist')(process.argv.slice(2))

// Path to yaml/json/toml config
const myConfigFilePath = path.join(__dirname, 'serverless-config.yml')

// Configorama can take file paths or JS objects.
const serverlessConfig = configorama.sync(myConfigFilePath, {
  options: cliFlags
})

module.exports = serverlessConfig