Cluster Energy Saving system (CLUES) is an energy management system for High Performance Computing (HPC) Clusters and Cloud infrastructures that supports integration with OpenNebula. The main function of the system is to power off internal cluster nodes when they are not being used, and conversely to power them on when they are needed.

The energy saving results obtained depends on the usage of each specific infrastructure, the scheduling policies and the workload patterns. But it will obtain nice savings in case that some of the nodes are eventualy underused.

The CLUES scheduler is the main component, as it has to take decisions with respect to when to switch nodes on/off, or how many of them are switched on at a time, over-provision to prevent peaks on the demand, etc. The system is integrated with the specific infrastructure at two levels:

• The CLUES system is integrated with the cluster management middleware by means of different plug-ins. The resource manager connectors provide a uniform way to interact with different resource managers (e.g. Torque/PBS or OpenNebula). Each plug-in consists of two parts:

1. A monitoring system, used by the engine to obtain information on the state of each node.
2. A job interceptor, that comes into action whenever a new job is to be submitted to a resource manager: before the job is actually submitted, the plug-in requests the necessary resources to the CLUES scheduler.

• The integration with the physical infrastructure by means of different connectors, so that nodes can be powered on/off using the techniques which best suit each particular infrastructure. The method to switch nodes on and off can be tailored to the particularities of each cluster. CLUES is shipped with IPMI and Wake-on-Lan to power on the nodes, and SSH to power them off. It can also be integrated with most of the specific Power Device Units (PDU).

When CLUES is working, some parameters should be tuned (e.g. frequency of checking the state, time to consider that a node is idle, etc.) to coordinate the VM scheduling policies of the site and the energy saving techniques.

Both CLUES ant the OpenNebula plug-in are avaliable for download at the developer’s website and it is distributed as open source under the GPL v3.0 license.