This Serverless plugin emulates AWS λ and API Gateway on your local machine to speed up your development cycles. To do so, it starts an HTTP server that handles the request's lifecycle like APIG does and invokes your handlers. Options passed on the command line override YAML options. List of available function names and their corresponding serverless.yml function keys are listed after the server starts. This is important if you use a custom naming scheme for your functions as serverless-offline will use your custom name. ...
...SockJS-client does require a server counterpart, such as SockJS-node, which is a SockJS server for Node.js. The API should follow HTML5 Websockets API as closely as possible. All the transports must support cross domain connections out of the box. It's possible and recommended to host a SockJS server on a different server than your main web site.