Disclosed embodiments relate to on-demand assignment of a web-server execution instance for a website server. Operations include storing generic website server code for hosting websites; storing website specific code unique to each of the websites; controlling a plurality of web-server execution instances, at least some of the instances running website specific code unique to at least one of the websites, and at least others of the web-server execution instances running the generic website server code devoid of the specific unique code for any one website; receiving a request to access a specific website; determining whether the specific website is already hosted, and if not, directing the request to a first one of the plurality of web-server execution instances and injecting into the first one of the plurality of web-server execution instances running the generic website server code, additional website specific code unique to the requested website.