First half of OpenTok NodeJS server

opentok-session.js

var fs = require('fs');
var server = express();
var OpenTok = require('opentok');

//Replace this with your OpenTok API key and OpenTok Secret
var opentok = new OpenTok('API_KEY', 'SECRET');

var SESSION_ID;
var QUALITY_SESSION_ID;

// Before starting server we need two OpenTok session id's
// one for quality testing and one for our call
console.log('Creating OpenTok quality session...');
opentok.createSession({mediaMode:"routed"}, function(error, result) {
  if (error) {
    console.log("Error creating quality session:", error);
    process.exit(1);
  } else {
    QUALITY_SESSION_ID = result.sessionId;
    console.log('Quality session created...');
  }
});
console.log('Creating OpenTok session...');
opentok.createSession({mediaMode:"relayed"}, function(error, result) {
  if (error) {
    console.log("Error creating session:", error);
    process.exit(1);
  } else {
    SESSION_ID = result.sessionId;
    fs.writeFile('last_session.id', SESSION_ID, function (err) {
      if (err){
        console.log("Error creating session:", err);
        process.exit(1);
      }
      
      // Session creation was successful,
      // now we start the server
      console.log('Session created...');
      start_server();
    });
  }
});