Juju is available on the command line as well as with an easy to install web user interface. The ecosystem provides a large number of charms (packages defining the services and their configuration as well as runtime hooks) and can be used from testing with local LXC containers up to Amazon, OpenStack, Azure, and more.
Sometimes the command line commands are a bit inconsistent and complex cloud solutions still remain complex (but definitely more simple than doing it by hand or with many other tools).
Try the demo to see how simple it can be used.
Any type of cloud based environments needing dynamic scalability (up and down).