It's great that Lex makes it so easy to integrate our chatbot into Facebook, Slack, and Twilio, but we might also want to have our chatbot integrate into other services that don't have built-in integrations. For this, we can create an API endpoint for sending messages to our Lex chatbot.
With AWS, we are lucky that they let you create an API with Lambdas and API Gateway. This means that we don't need to run a server, which means less work for us.