Methods, systems, and computer storage media for updating instances of a service application within nodes of a data center are provided. The system includes a state machine equipped for designating an earlier version of software running on some instances as a basement version and a newer version of software running on other instances as a latest version. The system also includes a compatibility mechanism responsible for allowing the basement version, the latest version, and other versions of the service application therebetween to interact using a data structure associated within the earlier version, or lowest common version of the service application. The compatibility mechanism is located apart from core logic of the service application. The activities of the state machine and the compatibility mechanism allow the instances to communicate with each other (using the lowest common version) while exposing just the validated version(s) of the service application to the client.