The execution of a distributed algorithm by a fixed size subset of nodes instead of the entire network is a strategy to build a scalable distributed network. For applications like blockchain, the selection protocol of this subset need to meet decentralization criteria by promoting the diversity of nodes in order to avoid the emergence of a third-thrust party. This paper introduces metrics to measure the decentralization of this selection protocol (based on standard deviation and the Gini index). In a second step and somewhat orthogonally, selecting closed nodes could reduce the execution latency of the algorithm. Thus, this paper proposes a new selection protocol that selects in real time closed nodes in the network whose results are verifiable and ensure high decentralization although the network may vary. Such a protocol is interesting to increase the number of validators in a blockchain with a hybrid based Byzantin Fault Tolerant consensus.