1. A method for placing objects on hosts in an online service, comprising: determining, using a processor, when to place an object on one of a plurality of hosts in the online service, wherein the online service comprises databases, virtual machines (VMs) and physical machines, wherein the physical machines are arranged in farms that perform roles in a network; obtaining placement constraints for the object that comprise hard constraints and soft constraints, wherein application of a hard constraint eliminates one or more of the hosts from being selected on which to place the object, and wherein soft constraints determine which hosts are more suitable than other hosts; applying the hard constraints against hosts within the network that results in a pool of remaining hosts, wherein the hard constraints include high availability constraints, wherein applying the high availability constraints eliminates one or more hosts to ensure that objects having redundant roles within the network are placed on different hosts; applying the soft constraints against the pool of remaining hosts that results in a pool of selection hosts; automatically selecting a host on which to place the object from the pool of selection hosts; and automatically deploying the object on the selected host.