title: Express 4 Sessions not persisting when restarting server
body: <p>I have an Express 4 app setup to have sessions.</p>
  
  <pre><code>// Sessions
  app.use(cookieParser());
  app.use(session({ secret: "some-secret" }));
  
  // Signup
  app.post("/signup", function (req, res) {
      create_user(req.body.user, function (err, user_id) {
          req.session.user_id = user_id;
          res.redirect("/admin");
      });
  });
  </code></pre>
  
  <p>When I submit the form, it saves the user_id to the req.session. However, when I restart the server, the session is gone.</p>
  
  <p>Why isn't it persisting? Am I missing some configuration?</p>