Isolate Single Service

During deployment and debugging it is helpful to run a single application or service or handle a sub-set of requests on 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:

To isolate a single AJAX service, for development or debugging, the MockServer can selectively forward specific requests to local instance of the 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": "simple-load-balancer",
  "version": "1.0.0",
  "main": "index.js",
  "dependencies": {
     "mockserver-node": "~1",
     "mockserver-client": "~1"
  }
}

Then create the index.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.*",
				        "headers": [
				            {
				                "name": "Host",
				                "values": "qa\\.environment\\.com.*"
				            }
				        ]
				    },
				    "httpForward": { // local machine Tomcat instance
				        "host": "127.0.0.1",
				        "port": 8080,
				        "scheme": "HTTP"
				    },
				    "times": {
				        "unlimited": true
				    }
				})
            	// forward all other request to QA environment
            	mockServerClient("localhost", HTTP_PORT).mockAnyResponse({
				    "httpRequest": {
				        "path": "/.*",
				        "headers": [
				            {
				                "name": "Host",
				                "values": "qa\\.environment\\.com.*"
				            }
				        ]
				    },
				    "httpForward": { // QA load balancer
				        "host": "192.168.50.10",
				        "port": 443,
				        "scheme": "HTTPS"
				    },
				    "times": {
				        "unlimited": true
				    }
				})
            });

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 install
node index.js