[Cthulhu_]

How is a .js file with a basic implementation of

  exports.handler = (event) => ({
    statusCode: 200,
    body: "Hello world: " + event.body
  })

vendor lock-in? You can hang this in an Express server yourself at any time. You can spin up your own three billion nodeJS servers yourself with this. The only thing Amazon does is hardware / instance management, load balancing and of course billing, which I don't see as vendor lock-in.