By default express and ejs are installed on the server. To use express there is a global variable named app. Do not create a new instance of express but use this global variable instead.
If you are using a different template engine such as jade. This module will likely be referenced from your cloud > node_modules folder. However at runtime, node.js will not be able resolve the jade module under your cloud > node_modules folder. To solve this, navigate to app actions > environment variables and set the variable name "NODE_PATH" and the variable value "/bundle/cloud/node_modules". When the "NODE_PATH" variable is set, node.js will resolve the jade dependency under your cloud > node_modules folder.