Instances of a same application execute on different respective hosts in a cloud computing environment. Instances of a monitor application are distributed to concurrently execute with each application instance on a host in the cloud environment, which provides user access to the application instances. The monitor application may be generated from a specification, which may define properties of the application/cloud to monitor and rules based on the properties. Each rule may have one or more conditions. Each monitor instance running on a host, monitors execution of the corresponding application instance on that host by obtaining from the host information regarding values of properties on the host per the application instance. Each monitor instance may evaluate the local host information or aggregate information collected from hosts running other instances of the monitor application, to repeatedly determine whether a rule condition has been violated. On violation, a user-specified handler is triggered.