Abstract-The article deals with the issues of the security of distributed and scalable computer systems based on the risk-based approach. The main existing methods for predicting the consequences of the dangerous actions of the intrusion agents are described. There is shown a generalized structural scheme of job manager in the context of a risk-based approach. Suggested analytical assessments for the security risk level in the distributed computer systems allow performing the critical t ime values forecast for the situation analysis and decisionmaking for the current configuration o f a distributed computer system. These assessments are based on the number of used nodes and data links channels, the number of act ive security and monitoring mechanisms at the current period, as well as on the intensity of the security threats realization and on the activation intensity of the intrusion prevention mechanis ms. The proposed comprehensive analytical risks assessments allow analyzing the dynamics of intrusions processes, the dynamics of the security level recovery and the corresponding dynamics of the risks level in the distributed computer system. Index Terms-Distributed computer systems, Security analysis, Risk-based approach. NOMENCLATURE α -the average intensity of the security threats for the distributed computer systems resources x1 and x2; β -the average intensity of the security mechanis ms from the group x3 and x4 activation; R 0 -the initial security risk; R(t) -security risks in the distributed computer systems, changing at time t;x 1 -the number of nodes in the distributed computer system;x 2 -the number of data link channels;x 3 -the number of the active security mechanisms; x 4 -the number of the security monitoring tools in the distributed computer systems;x 1max -the maximu m nodes number in a distributed computer system; x 2max -the maximu m number of data link channels; x 3max -the maximu m nu mber of the active security mechanisms;x 4max -the maximu m nu mber o f the security monitoring tools in the distributed computer systems.

In this paper, we present the development of a decentralized mechanism for the resources control in a distributed computer system based on a network-centric approach. Intially, the network-centric approach was proposed for the military purposes, and now its principles are successfully introduced in the other applications of the complex systems control. Due to the features of control systems based on the network-centric approach, namely adding the horizontal links between components of the same level, adding the general knowledge control in the system, etc., there are new properties and characteristics. The concept of implementing of resource control module for a distributed computer system based on a network-centric approach is proposed in this study. We, basing on this concept, realized the resource control module and perform the analysis of its operation parameters in compare with resource control modules implemented on the hierarchical approach and on the decentralized approach with the creation of the communities of the computing resources. The experiments showed the advantages of the proposed mechanism for resources control in compare with the control mechanisms based on the hierarchical and decentralized approaches.One of the main components of resource control system (RCS) of DCS is a scheduler which coordinates the solution of the tasks that arrive for processing to the distributed system by placing them on available computing resources [7]. It is important to meet the requirements of the user and to avoid the idles for the computational resources [8]. In [7] there are identified the following key characteristics of the DCS scheduler: the run time of the task, DCS performance and the response time of the system.In recent years, there was devoted much attention to the study of decentralized resource control techniques for the distributed computer systems to improve the performance of the DCS in the context of its scalability and reliability [9]. In [9] are described the comparative analysis of the existing decentralized distributed computer systems and the mechanisms that are used for resource control. This study contains a comparative analysis of mechanisms of resource control of DCS in different contexts.Additionally, [10,11,12] presents more recent developments of DCS resources control systems, that are implemented on a decentralized basis.The development in [11] uses the exchanges of network messages between DCS compute nodes for the organization of distributed computing. The messages of several types come, each of which provides a specific functions of the algorithm for the resources allocation. This planning framework supports several heuristic algorithms and it also provides the load balancing for the DCS nodes.In [12] there is considered the DCS, which consists of heterogeneous computing elements (CE), which are interconnected by a computer network. In addition to CE, the system has passive nodes, the so-called "Bulletin boards", which are used to allocate users tasks and to collect some service in...

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