On-demand
At any time that someone wants or needs something done or happening whenever somebody asks, when needed or asked for, as in
She's always ready to sing on demand, or Nowadays infants are generally fed on demand [Dictionary.com].
This usage broadens this phrase's meaning in finance, that is, “payable on being requested or presented,” as this note is payable on demand.
On-demand service, in the context of IT, is an excellent facility and feature of cloud computing services, which allows users to provision raw cloud resources at run time, when and where needed. On-demand service allows end users to use cloud computing, storage, software, and other resources instantly and often without limits. This addition of resources is generally performed in live environments through a transition process that doesn’t affect current operations [Techopedia].
On-demand definition & meaning. Dictionary.com. Retrieved from: https://www.dictionary.com/browse/on--demand
What is on-demand service?. Techopedia. Retrieved from: https://www.techopedia.com/definition/26711/on-demand-service