title: process.env.PORT is undefined (in LinuxCloud environment)
body: <p>I've been developing a nodejs app on C9 for some time and now I'm trying to make a copy of it on my remote host. So far, in the new environment <code>node app.js</code> works in the console but I am unable to view the website in my browser.</p>
  
  <p>It seems that it is a port issue.
  My app.js file goes like this :</p>
  
  <pre><code>var express     = require("express"),
      app         = express();
  (...)
  app.listen(process.env.PORT, process.env.IP, function(){
     console.log(process.env.PORT);
     console.log("The YelpCamp Server Has Started!");
  });
  </code></pre>
  
  <p>In the C9 environment, the log tells me that process.env.PORT is 8080. But in the new environment, the log tells me that process.env.PORT is undefined.</p>
  
  <p>How can I fix this ?</p>
  
  <p>This is similar to this older <a href="https://stackoverflow.com/questions/45550262/process-env-port-is-undefined">question</a> except that my remote OS is Linux not Windows. The answer to this question says that one should "modify the web.config file", but I couldn't find it on my remote host and I'm not sure it works the same way under Linux and under Windows.</p>