You create a Slider application package, deploy it to a YARN cluster and manage it. From the management perspective it is primarily flexing. Based on needs (and the architecture of the application) you grow or shrink specific components of your long running application from time to time. Of course you can set some constraints like affinity, anti-affinity, and strict placement (for data locality or other reasons). Some of these are handled very well by Slider, others are best efforts.
However long running applications have an inherent need to be auto (or even self) managed. This can be achieved by a custom management tool, interacting with Slider client based on constant feedback on the health of the application (metrics, alerts, etc.). This is primarily reactive management.
There is also proactive management, where the application owner is aware of the usage pattern of the application over time. For example, a financial application usage peaks between 8am to 4pm Mon to Sat (local time), and slows down at other times. A tax application usage peaks for a few months prior to April 15 and then slows down for several months. Certain healthcare applications peak during flu season. You get the point!
It should be possible to declaratively define such an application usage skyline, which can be fed to Slider and put an application on cruise control. The specification can be modified dynamically and Slider should honor the modified version for (reasonably acceptable) future state of the application.
This kind of feature would need support from YARN. There should be a way for Slider to provide details to YARN for guaranteed future capacity planning.
Note: It is the negotiation that Slider will do with YARN, to ensure the guaranteed (or best effort) future capacity planning to maintain the skyline is what makes this pro-active management useful. Nothing stops an application owner to write pro-active tools to manage a skyline.