Virtual Machine Monitor Rejuvenation Research Articles

A Model for Availability and Security Risk Evaluation for Systems With VMM Rejuvenation Enabled by VM Migration Scheduling

Most companies and organizations rely nowadays on virtualized environments to host and run their applications. Some of these applications have stringent availability and security requirements. An important challenge for high availability in virtualized systems is software aging, which can lead the system to hangs or other types of failures. Software rejuvenation is applied to cope with software aging problems, whereas previous research suggests the use of Virtual Machine (VM) migration to reduce the downtime related to Virtual Machine Monitor (VMM) software rejuvenation. However, there is still a gap regarding the security implications of applying VM migration scheduling as support for VMM software rejuvenation. In this paper, we propose a security evaluation approach based on an availability model for virtualized systems with VM migration for VMM rejuvenation. The goal is to find the proper rejuvenation scheduling to reach the desired levels (or at least to avoid the undesired levels) of security risk and availability. We present three case studies comprising major security threats, namely Man-in-the-middle and Denial of Service attacks. Results provide insightful information regarding the tradeoff between availability and security risk when applying VM migration scheduling for rejuvenation purposes.

Models for availability and power consumption evaluation of a private cloud with VMM rejuvenation enabled by VM Live Migration

Software aging affects the availability of Virtual Machine Monitor (VMM), one of the main components of virtualized environments. Software aging causes internal software degradation due to bugs activation and accumulation during its execution. Software rejuvenation implemented through Virtual Machine (VM) Live Migration may be applied to cope with software aging effects on cloud computing system. Another relevant problem is the power consumption of using software rejuvenation techniques in the virtualized environments. This paper presents availability models based on Stochastic Petri Nets to evaluate two VM Live Migration approaches. These approaches are based on the redundancy schemes: Warm-Standby and Cold-Standby. In the Cold-Standby migration, the migration target machine is started only before the VM Live Migration. In the Warm-Standby Migration, the migration target machine runs along with the source migration machine. Results show that VM Live Migration causes a significant improvement in system availability. Scenarios with a heavy workload present an annual downtime reduction of 164 h. The availability comparison between two approaches reveals that the Cold-Standby approach has a slightly better result due to the decrease in the total number of VM Live Migrations. The power consumption results show that Cold-Standby approach is more efficient in power consumption. In all the observed scenarios, the costs savings by using Cold-Standby approach exceed 40%. The highlights of this paper are: i) a comprehensive model for availability evaluation of cloud computing with VMM rejuvenation through VM migration scheduling; ii) sensitivity analysis to define proper rejuvenation scheduling to maximize system availability and iii) power consumption comparison of the two adopted migration approaches.

Optimised Migrate Virtual Machine Rejuvenation

Server virtualization is an essential component in virtualized software infrastructure such as cloud computing. Virtual machines are generated through a software called virtual machine monitor (VMM) running on physical servers. The risks of software aging caused by aging-related bugs affect both VM and VMM. As a result, service reliability degrades may generate huge financial losses to companies. This paper presents an analytic model using stochastic reward nets for timebased rejuvenation techniques of VMM and VM. We propose to manipulate the VM behavior while the VMM rejuvenation is according to the load on the system. Using a previous Petri net model of virtualized server, we performed an algorithm in order to optimize rejuvenation technique and achieve high availability. So we perform Migrate-VM rejuvenation or Warm-VM rejuvenation while there are current jobs in the system. Although Migrate-VM rejuvenation is better than Warm-VM rejuvenation in steady state availability, it can’t be always performed as it depends on the capacity of the other host. When the queue is empty and the virtual machine has no current jobs to serve, we propose to combine both VMM rejuvenation and VM rejuvenation. We show that the proposed technique can enhance the availability of VMs.

Job completion time on a virtualized server with software rejuvenation

This article analyzes the completion time of a job running on a virtualized server subject to software aging and rejuvenation in a virtual machine monitor (VMM). A job running on the server may be interrupted by virtual machine (VM) failure, VMM failure or VMM rejuvenation. The job interruption is categorized as either preemptive-repeat ( prt ), in which case the interrupted job needs to restart from the beginning, or preemptive-resume ( prs ), in which case the job resumes execution from the point of interruption. Using a semi-Markov process (SMP) to model the server behavior, the steady-state server availability is computed and the theory developed in Kulkarni et al. [1987] is used to obtain the Laplace-Stieltjes transform (LST) of the job completion time. In the numerical experiments, we introduce four types of aging behavior of VMM. The effectiveness of VMM rejuvenation on job completion time is discussed in association with the type of interruption it causes and the VMM aging type. With our parameter settings, VMM rejuvenation with prs job interruption improves the performance of job execution regardless of the aging type, with performance degradation is taken into account.

Availability Modeling and Analysis of a Single-Server Virtualized System with Rejuvenation

Availability of business-critical application servers is an issue of paramount importance that has received special attention from the industry and academia in the last decade. This paper presents two stochastic reward net based availability models for a single-server virtualized system. The similarity in both models is that software rejuvenation is applied at not only virtual machine monitor (VMM) level using a time-base policy but also at virtual machines (VMs) using a prediction-based policy. The key difference is that the passive software replication and the active software replication are respectively adopted at the VM level of both models. We compare these models in terms of steady-state system availability by numerical analysis. Results show steady-state system availability with the active replication style gets a bit better than that of the passive one. Further, we study the impact of two critical parameters, the VMM rejuvenation interval and the VM aging detection probability, on downtime and on the number of transaction lost by sensitivity analysis.

Workload-Based Software Rejuvenation in Cloud Systems

Cloud computing is a promising paradigm able to rationalize the use of hardware resources by means of virtualization. Virtualization allows to instantiate one or more virtual machines (VMs) on top of a single physical machine managed by a virtual machine monitor (VMM). Similarly to any other software, a VMM experiences aging and failures. Software rejuvenation is a proactive fault management technique that involves terminating an application, cleaning up the system internal state, and restarting it to prevent the occurrence of future failures. In this work, we propose a technique to model and evaluate the VMM aging process and to investigate the optimal rejuvenation policy that maximizes the VMM availability under variable workload conditions. Starting from dynamic reliability theory and adopting symbolic algebraic techniques, we investigate and compare existing time-based VMM rejuvenation policies. We also propose a time-based policy that adapts the rejuvenation timer to the VMM workload condition improving the system availability. The effectiveness of the proposed modeling technique is demonstrated through a numerical example based on a case study taken from the literature.

Modeling and analysis of software rejuvenation in a server virtualized system with live VM migration

As server virtualization is used in a number of IT systems, the unavailability of virtual machines (VM) on server virtualized systems becomes a significant concern. Software rejuvenation is a promising technique for improving the availability of server virtualized systems as it can postpone or prevent failures caused by software aging in both the VM and the underlying virtual machine monitor (VMM). In this paper, we study the effectiveness of a combination of VMM rejuvenation and live VM migration. When a VMM needs to be rejuvenated, the hosted VMs running on the VMM can be moved to another host using live VM migration and continue the execution even during the VMM rejuvenation. We call this technique Migrate-VM rejuvenation and construct an availability model in the stochastic reward net for evaluating it in comparison with the conventional approaches; Cold-VM rejuvenation and Warm-VM rejuvenation. The designed model enables us to find the optimum combinations of rejuvenation trigger intervals that maximize the availability of VM. In terms of the maximum VM availability, Migrate-VM rejuvenation is potentially the best approach. However, the advantage of Migrate-VM rejuvenation depends on the type of live VM migration (stop-and-copy or pre-copy) and the policy for migration back to the original host after VMM rejuvenation (return-back or stay-on). Through numerical examples, we show that “pre-copy” live VM migration is encouraged rather than pure “stop-and-copy” migration and it is better to return back VM to the original host soon after the VMM rejuvenation (i.e., “return-back” rather than “stay-on” policy) for high-availability. The effect of the VMM rejuvenation technique on the expected number of transactions lost is also studied by combining the availability model with an M/M/1/n queueing model.