Abstract: A computer network monitoring controller for monitoring the performance of a plurality of virtual machines in a cloud computing environment, each virtual machine being a set of resources hosted on a hardware platform and arranged to appear as a real hardware to a client, the virtual machines being allocated and generated by a management system, the monitoring controller comprising: a plurality of interfaces, each one connected to a monitoring system having links to at least one of the virtual machines, and each monitoring system being arranged to capturing event messages relating to the status of the virtual machine and outputting these event messages in a monitoring system specific format; an data store for storing event messages received from each of the monitoring systems via the interfaces; a receiver for receiving monitoring requests from said management system, each request specifying monitoring requirements relating to at least one of the virtual machines; a converter for converting the messages from t