When openflow plugin device connect to all the three controllers in cluster, instance for which instantiateServiceInstance() is called will send the MASTER role request to the device. But there is no way for other two instances to know when to send the SLAVE role, because closeServiceInstance() won't be call for those and that make sense looking at the purpose of the API. Also there is no API for candidates to enquire if is there any existing instance that is active for the register service entity, so it can assume that it's a non-active/non-owner instance and it can send the slave role to the device. In the current implementation of openflowplugin we are using timeout task to check if the the service entity is owner or not, and in my opinion it's very bad approach. I think Singleton service should either provide an API to enquire the ownership status of the service entity or it should call the closeServiceInstance() if it's not an active instance.