On-demand web-server execution instance for website hosting with custom back-end functionality

An online website building system includes: an online database configured to store a library of website building elements for configuring a front-end of a webpage, the webpage having been built on a platform including at least common server code; and store rules for accessing code associated with the website building elements; and at least one processor configured to enable the user to edit code associated with a webpage, and to provide a programmable event for activating the resultant user-editable code, wherein the user-editable code is configured to provide dynamic customized back-end functionality associated with the webpage; store the edited user-editable code in a code storage system in communication with the online database; receive a request to access the webpage, and in response to the request and before the request times out, provide access to a virtualized execution instance comprising at least the common server code and the edited user-editable code.