Download - Resource Allocation using Virtual Machine Migration: A Survey

Poster Paper

© 2013 ACEEEDOI: 03.LSCS.2013.2.

Proc. of Int. Conf. on Advances in Information Technology and Mobile Communication 2013

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Resource Allocation using Virtual Machine Migration:A Survey

Ts‘epo Mofolo1, R. Suchithra2, N. Rajkumar3

1,2MS (IT) Department Jain University, Bangalore, India{mofolotc, suchithra.suriya}@gmail.com

3Department of Software Engineering Ramakrishna College of Engineering, Coimbatore, [email protected]

Abstract- As virtualization is proving to be dominant inenterprise and organizational networks there is a need foroperators and administrators to pay more attention to livemigration of virtual machines (VMs) with the main objectiveof workload balancing, monitoring, fault management, low-level system maintenance and good performance with minimalservice downtimes. It is also a crucial aspect of cloud computingthat offers strategies to implement the dynamic allocation ofresources. Virtualization also enables virtual machinemigration to eliminate hotspots in data centers .However thesecurity associated with VMs live migration has not receivedthorough analysis. Further, the negative impact on servicelevels of running applications is likely to occur during thelive VM migration hence a better understanding of itsimplications on the system performance is highly required.In this survey we explore the security issues involved in livemigration of VMs and demonstrate the importance of securityduring the migration process. A model which demonstratesthe cost incurred in reconfiguring a cloud-based environmentin response to the workload variations is studied. It is alsoproved that migration cost is acceptable but should not beneglected, particularly in systems where service availabilityand response times are imposed by stringent Service LevelAgreements (SLAs). A system that provides automation ofmonitoring and detection of hotspots and determination ofthe new mapping of physical to virtual resources and finallyinitiates the required migrations based on its observations isalso studied. These are experimented using Xen VirtualMachine Manager. Migration based resource Managers forvirtualized environments are presented by comparing anddiscussing several types of underlying algorithms fromalgorithmistic issues point of view.

Keywords: Virtualization, Migration, Virtual Machines,allocation, resources.

I. INTRODUCTION

Live migration of virtual machines (VMs), the process ofmirroring a VM from one Virtual Machine Manager (VMM)to another without stopping the execution of a guest operatingsystem, often between different physical hosts has resultedin new opportunities in traditional computing as well CloudComputing. Live migration is of great importance in achievingfactors such as high-availability of services, transparentmobility, consolidated mobility and workload balancing. [1,6, 7]

Virtualized infrastructures have proved to be a keycomponent to drive the emerging Cloud Computing paradigm.Migration of VMs aims at improving the manageability,

performance and fault tolerance of systems. Reasons thatjustify VM migration in a production system include: theneed for a balanced system workload, which can be achievedvia migrating VMs out of overloaded or overheated serversand the need to power off servers for maintenance aftermigrating their workload other servers. Hypervisors such asXen and VMWare allow the migration of a VM while it stillcontinues to provide services to various applications [4, 8, 9,12].

The greatest advantage of live migration is the possibilityto migrate a VM with near-zero downtime, a crucial featurewhen applications are being served. [4]Clouds have aremarkable advantage over traditional data centers inproviding elasticity as well as attaining high resourceutilization. A customer has the ability and flexibility ofincreasing and decreasing the amount of resources it requiresfor itself. For a cloud provider, elasticity is the ability totransparently exchange resources from one customer toanother in response to variations in demand thus enablingthe cloud to operate at high resource utilization. [2]Thefollowing benefits are provided by live migration in multipleVM-based environments: [10, 11] Load balancing, onlinemaintenance and proactive fault tolerance and powermanagement.

Live migration introduces some significant securitychallenges. A VMM that facilitates a vulnerableimplementation may lead to the exposure of both the guestand host operating system attacks and hence result inabsolute system integrity compromise. Reconfigurations(dynamic allocation) in a cloud may result in performanceissues from hosted applications. It consumes resources andmay result in resource contention for applications. Hence itis of utmost importance to have a thorough understandingof the following aspects:(i) The frequency of reconfigurations in typical cloudenvironment(ii) The impact of certain reconfigurations on the hostedapplications [2]

The dynamic resource allocation requirements of aworkload can be satisfied by changing the capacity of a virtualmachine at runtime. The pre-copy algorithm [3, 12] addressesthe issue of downtime by reducing it to the magnitude ofmilliseconds. There are other issues which remain unresolvedthough:

When the rate at which pages are dirtied is faster thanthat of pre-copy process, all pre-copy work will be ineffi

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cient. This would mean memory-intensive applications wouldnot benefit from pre-copy algorithm and the downtime mayincrease to several seconds. This drawback makes the algo-rithm applicable in high speed LANs. A novel live migrationis proposed. The main objective is to minimize the migrationdowntime and network bandwidth consumption and this isimplemented based on full-system trace and replay system-Revirt. [13] Checkpointing/recovery and trace/replay tech-nology is adopted to provide fast, transparent VM migrationin both LAN and WAN environments. A trace daemon isdeployed and continuously keeps logs of the non-determin-istic events of the VM while sacrificing very little perfor-mance. The execution trace file logged at the original host isiteratively mirrored to the target host and used to synchro-nize the migrated VM’s execution state. [10]Other factors tobe considered include the total migration during which stateon both the source and target hosts is synchronized andhence may affect system reliability. Further, it has to be en-sured that migration does not interfere with active servicesthrough resource contention for instance CPU and networkbandwidth with the migrating OS.

This can be achieved through pre-copy algorithm in whichpages of memory are mirrored iteratively from the source hostto the target host, all without stopping the execution of thevirtual machine being migrated. The final stage pauses theVM, mirrors only remaining pages to the target host andrestarts execution there as explained Clark et al. General livemigration process based management system is presented inthis paper. [5]Impact of reconfiguration in a cloud setting hasbeen studied and a model presented to characterize it.

II. GENERAL LIVE MIGRATION PROCESS USING RESOURCE

MANAGER

This section presents the major phases for a general VMlive migration process which use a resource manager. Themain focus is on operating system virtualization. On everyphysical host there is a resident Virtual Machine Manager(VMM), also known as a hypervisor which enables manyvirtual machines to have the physical system resources. Theprocess of migrating VMs is carried out by the VMM. In ashared hosting model an individual application is representedby one VM, however there are situations where it can berepresented more than one VM. [15, 16]

The resource manager execution occurs in iterations. Inevery iteration, three major phases occur:

A. The Pre-allocation PhaseThe main responsibility of the VMM is to gather usage

data from the executing nodes within a predefinedmeasurement interval by using a particular monitoring tool.The features of this tool depend mainly on the adoptedvirtualization technology and the needed data to be collected.Through these gathered data, the VMM can keep a generalview about the performance in the executing nodes. Re-allocation is initiated if there are violations of the predefinedtriggering conditions.

B. The Migration Planning PhaseThis is the most sensitive part of the processing. The

VMM has to produce a convenient migration plan. A typicalmigration plan consists of source physical host(s), VM(s) tobe migrated and the physical host(s).

C. The Migration Execution Phase It is the responsibility of the VMM to put the migration

plan into action. The specific details of this phase depend onthe adopted virtualization technology.

III. DESIGN CONSIDERATIONS ON LIVE VM MIGRATION

Migrating VMs in cluster server environments leads toconsideration of the physical resources used in sucharchitectures, in particular, the memory, network and disk.

A. Migrating Memory“Reference [3]”, Clark et al, Mirroring VM’s memory from

one physical host to another can be performed in severalways. When a VM is executing a live service, this mirroringprocess has to be carried out in way that strikes a balance ofthe requirements of minimizing the downtime and totalmigration time. Downtime will be directly observable to theend users of the VM as service disruption.Memory transfer is achieved in three phases:

Push phase: The source VM continues its execution whilecertain memory pages are pushed across the network to thetarget physical host. Memory pages modified (dirtied) duringthis process must be resent in order to ensure consistency.

Stop and copy phase: The source VM is halted and pagesof memory are copied to the target host and the execution ofthe new VM is started on the physical target host.

Pull phase: The new VM executes, and if it accesses amemory page that has not yet been mirrored this page ispulled across the network from the source VM. The stop-and-copy mechanism means downtime and total migrationtime are directly proportional to the amount of physical memoryallocated to a VM. This is highly likely to result in detrimentaloutage if the VM is executing a live service. The pre-copymechanism balances these issues by combining aparameterized iterative push phase and a very short stop-and-copy phase. Iteratively scanning and transferring a VM’smemory image between two physical hosts in a cluster couldsubsequently consume the entire network bandwidthavailable between them and deprive the executing servicesof resources. The service degradation is likely to occur to acertain extent during any live migration process. This issueis addressed by employing strategies that ensure that thelive migration process does not disrupt the active traffic orany processing.

B. Local ResourcesConsidering network resources, it is desirable that the

migrated VM should have all network connections openwithout any dependencies on forwarding techniques on theoriginal host, which maybe shutdown after the migrationprocess. A migrating VM will include the protocol state and

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will still retain its IP address when migrated.

C. Design OverviewIn Figure 1 the migration process is viewed as a

transactional interaction between two physical hosts underconsideration as presented by to Clark et al [3].

Figure 1: VM Migration Timeline

Step 0: Pre-Migration The process begins with VMexecuting on source physical host A. A target host maybepreselected and has to have enough resources by the migratedVM.

Step 1: Reservation A request to migrate VM from host Ato host B is issued. Resources available on B are verified anda container for VM’s size is reserved.

Step 2: Iterative Pre-Copy All pages are transferred fromA to B. During round n, pages dirtied during round n-1 aretransferred.

Step 3: Stop-and-Copy VM in A is halted for a while andits network traffic is redirected to B. The VM copy at A is stillconsidered to be primary and can be resumed in case ofmigration failure.

Step 4: Commitment Host B acknowledges to A that ithas successfully received a consistent copy of the VM. HostA acknowledges B’s message as commitment of the migrationprocess. Host A can get rid of the original VM B takes over asthe primary physical host.

Step 5: Activation The VM that resides on B is activated.Post-migration code is executed to advertise the migrated IPaddress. This technique ensures that at least one physicalhost has a consistent VM copy during the entire migrationprocess according to Clark et al [3].

IV. ANALYSIS OF RESOURCE MANAGEMENT ALGORITHMS

Algorithms that are used to implement the surveyed live

migration based on the resource manager are thoroughlyanalyzed in this section. [5]

A. Ordering algorithmsThese algorithms should allow the resource manager to

answer questions such as: from where to migrate? WhichVM to migrate? Where to migrate? Ordering algorithms suchas Dynamic Management Algorithm (DMA) have somelimitations. Using DMA makes it impossible to judge theperformance of the resource manager under network intensiveapplications. The Fuzzy Decision making model based onTOPSIS techniques suffers from the problem of timeconsuming calculations. In [14] management algorithms forcloud computing paradigm are proposed. A load-trend basedsorting algorithm is used to select candidate VMs formigrations and the target hosts. It distributes the migratedVMs by assigning each receiving host only one VM. Thisleads to avoidance of load balance shifting, which is anunwanted implication that results in frequent fluctuationsthat negatively impact the system performance and stability.

B. Constraint ProgrammingIt has the limitations of only considering only viableprocessing nodes and CPU-memory resources. The exploredresource manager (Entropy) has the capability to combineand automate application provisioning problem. However thisalso has a problem of being limited to CPU-memory dimensions.

C. Genetic Algorithms (GAs)Gas based model enables for multiple-SLA representation

for each VM. The main challenge of Gas results from theinfeasible solutions that can appear as a byproduct of theevolution process.GA based approach is flexible and fasterfor VM packing problems and represents a promisingmechanism. It can greatly fasten constraint programmingexpensive processing.

V. CONCLUSION

Virtualization is a significant technology that can be de-ployed in data centers and cloud platforms to provide pow-erful resource allocation strategies. In this paper we surveyedthe benefits offered by VM machine migration in resourceallocation. Challenges associated with the VM migration havealso been explored including the security threats inherent inlive VM migration. Strategies and techniques to overcomethese issues have also been outlined. The checkpointing/recovery and trace/replay technology provides fast and trans-parent VM for both LAN and VM environments and thisgives it a good advantage over other migration strategies.[10]The Xen VMM provides rapid transfer of interactiveworkloads within clusters and data centers. The total down-time is also reduced below thresholds. [1] Access controlpolicies should be provide administrators with the privilegesto manage the migration process. Techniques that ensurevery little utilization of resources by the migration processshould be developed as it leads to high downtime and subse-quently service degradation and this is not desirable in cloud

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platforms. Dynamic consolidation methods which aim at mini-mizing number of migrations as much as possible should beemployed in cloud computing. This should enable achieve-ment of high resource utilization.

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