During deployment and debugging it can be helpful to run a single application or service or handle a sub-set of requests on a local machine in debug mode. Using MockServer it is easy to selectively forward requests to a local process running in debug mode, all other request can be forwarded to the real services for example running in a QA or UAT environment.

For example a single page application may load static resources such as HTML, CSS and JavaScript from a web server and also make AJAX calls to one or more separate services, as follows:

Single Page Application

To isolate a single AJAX service, for development or debugging, the MockServer can selectively forward specific requests to a local instance of the service:

Isolating Single Service

One of the simplest ways to do this is using Node.js. In the example below all requests matching path "/rest.*" (i.e. starting with /rest) will go to the local machine on port 8080 whereas all other requests will go to a remote machine (i.e. a load balancer or remote server) on ip 192.168.50.10 and port 443.

First create a package.json file as follows:

{
  "name": "mockserver_as_reverse_proxy",
  "version": "1.0.0",
  "main": "server.js",
  "dependencies": {
    "mockserver-node": "5.4.1",
    "mockserver-client": "5.4.1"
  }
}<

Then create the server.js file that starts MockServer and sets up the forwarding rules as different expectations, as follows:

var mockserver = require('mockserver-node');
var mockServerClient = require('mockserver-client').mockServerClient;
var HTTP_PORT = 1080;

mockserver
    .start_mockserver({
        serverPort: HTTP_PORT
    })
    .then(function () {
        // forward backend REST API request to local machine
        mockServerClient("localhost", HTTP_PORT)
            .mockAnyResponse({
                "httpRequest": {
                    "path": "/rest.*"
                },
                "httpForward": { // local machine Tomcat instance
                    "host": "127.0.0.1",
                    "port": 8080,
                    "scheme": "HTTP"
                },
                "times": {
                    "unlimited": true
                }
            })
            .then(
                function () {
                    // forward all other request to QA environment
                    mockServerClient("localhost", HTTP_PORT)
                        .mockAnyResponse({
                            "httpRequest": {
                                "path": "/.*"
                            },
                            "httpForward": { // QA environment load balancer
                                "host": "192.168.50.10",
                                "port": 443,
                                "scheme": "HTTPS"
                            },
                            "times": {
                                "unlimited": true
                            }
                        })
                        .then(
                            function () {
                                console.log("created expectations");
                            },
                            function (error) {
                                console.log(error);
                            }
                        );
                },
                function (error) {
                    console.log(error);
                }
            );
    });

console.log("started on port: " + HTTP_PORT);

// stop MockServer if Node exist abnormally
process.on('uncaughtException', function (err) {
    console.log('uncaught exception - stopping node server: ' + JSON.stringify(err));
    mockserver.stop_mockserver();
    throw err;
});

// stop MockServer if Node exits normally
process.on('exit', function () {
    console.log('exit - stopping node server');
    mockserver.stop_mockserver();
});

// stop MockServer when Ctrl-C is used
process.on('SIGINT', function () {
    console.log('SIGINT - stopping node server');
    mockserver.stop_mockserver();
    process.exit(0);
});

// stop MockServer when a kill shell command is used
process.on('SIGTERM', function () {
    console.log('SIGTERM - stopping node server');
    mockserver.stop_mockserver();
    process.exit(0);
});

To start the process install the npm module and launch Node.js, as follows:

npm i
node server.js