Towards a Framework for the Autonomic Management of Virtualization-Based Environments

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1 Towards a Framework for the Autonomic Management of Virtualization-Based Environments Dan Marinescu and Reinhold Kroeger Wiesbaden University of Applied Sciences Distributed Systems Lab Kurt-Schumacher-Ring 18, D Wiesbaden, Germany {dan.marinescu,kroeger}@informatik.fh-wiesbaden.de Abstract Over the past years, virtualization has emerged again, making its place in the data centers. However, data centers are already facing management problems due to the increased system complexity. Virtualization increases this complexity even more. To address these management problems, computing systems should be able to manage themselves. In this paper, we propose a modular framework for the autonomic management of virtualization-based environments. This framework is virtualization-technology independent and permits plugging in various controller approaches. 1. Introduction System virtualization is a technique first developed in the mid 1960 s. It consists of an indirection layer that is introduced between the hardware and the operating system, called virtual machine monitor (M) or hypervisor. The M partitions the hardware in logical units, called virtual machines (s). Inside a, a so-called guest operating system is running. The M controls and synchronizes the access of guest OSs to hardware resources. As such, it is possible to run multiple, possibly different OSs in parallel on the same hardware. Although a flourishing technology in the 1970 s, the 1980 s and 1990 s brought a drop in hardware prices which meant that it was affordable to run one application per computing system, and thus virtualization was slowly forgotten [10]. Over the past years howvever, virtualization has emerged again, nowadays being used on both server (e.g. ware ESX [19], Xen [23]) and desktop systems (e.g. Ware Workstation [20], Virtual Box [18]). The new paradigm states: one application per virtual machine, several virtual machines per computing system. The adoption of virtualization in the data center is taking place at a high pace. The possibility of consolidating a bundle of under-utilized server boxes into one server system is certainly one of the reasons. Besides server consolidation, it is the way maintenance and system management are simplified that makes this technology attractive for system administrators. However, virtualization does not reduce the complexity of a system. In fact, having multiple virtual machines running on top of several physical machines actually increases the overall system complexity. This matches the theory of the ever increasing complexity of computing systems, which will finally lead to systems which cannot be managed by human experts (system administrators) any more. However, such systems exist in the nature since millions of years. In [6], the authors proposed the human autonomic nervous system (ANS) as an inspiration source. The ANS manages low-level, yet vital body functions like heart rate or body temperature without conscious control. Similarly, computing systems should be able to manage themselves, based on some high-level goals defined by a human system administrator. The field of reseach that deals with this kind of systems is called autonomic computing, the essence of which is self-management. According to [6], there are four aspects of self-management: self-configuration, the capability of computing systems to install and configure themselves self-optimization, the property of computing systems to continuously seek to improve their operation self-healing, the property of computing systems to detect, diagnose and repair local problems self-protection, the property of computing systems to defend themselves in the face of a malicious attack or cascading failures For the purpose of this paper, we will mainly focus on the self-optimization aspect for the management of

2 virtualization-based environments, assuming that qualityof-service levels of the services, provided by the s, have to be fulfilled [3]. Virtualization-based environments are a great area of application for autonomic computing. On one hand, the increased complexity caused by the use of virtualization makes autonomic computing a necessity in large data centers. On the other hand, most of the server virtualization technologies that currently exist provide management features like the allocation of resources (memory, CPU shares and others) at run-time and live migration of virtual machines [2]. These features are great control knobs (actuators) that can be used for system self-optimization. Also monitoring and debugging capabilities are enhanced by the introduction of an indirection layer between the operating system and the hardware. What is missing is an intelligent controller that can take decisions based on the data gathered through monitoring resulting in dynamically allocated resources through the previously mentioned actuators. This paper deals with aspects related to the development of such an intelligent controller. 2. Related work and limitations Various publications deal with the autonomic management of virtual environments. Policy-based approaches have been a popular way to manage computing systems, and virtualization-based systems are no exception. In [12], the authors present a system called VIOLION, which uses the Xen hypervisor for virtualization. The system comprises one monitor daemon per physical machine and one adaptation manager. The adaptation manager uses the data gathered by the monitor daemon to dictate virtual machine resource allocation. Another policy-based approach has been published by Grit et al. [4]. Here, the authors use and extend Shirako, a Java-based toolkit for resource leasing services, to explore algorithmic challenges when using policies for the adaptive hosting of virtual machines on computer clusters. Control theory has also been used to autonomically manage virtual environments. Zhang et al. [24] present a control-theoretic model for adaptation, based on the idea that the s are responsible for adjusting their demand for resources, with respect to efficiency and fairness. In [9], the authors use a feedback-control strategy to address dynamic resource allocation problems. The approach uses an infrastructure based on Xen, RUBiS [11] and TPC-W [16]. Time series analysis can be used to forecast the behaviour of a virtualization-based system. Bobroff et al. [1] present a mechanism for the dynamic migration of virtual machines based on the forecasted load. Menascè et al. [8] use an approach based on utility functions [21] for the dynamic CPU allocation to virtual machines. The authors test their approach by means of simulations, using historical data. These publications represent the first steps taken by the research community to develop various strategies for an intelligent controller based on different control paradigms. It is however hard to objectively evaluate these strategies. The various publications use different architectures, perform different tests and some even only use historical data and simulation to test how their strategies perform. In this context, it is impossible to say that one approach performs better than another, or that some approach is more adequate in a specific situation than the other approaches. The main reason for this is that automated management of environments is not mature yet but still in its infancy. We argue that the only way to solve this problem is to design a common framework for the development and evaluation of autonomic computing strategies for virtualization-based distributed environments. 3. Architecture of the framework A framework for developing and evaluating autonomic computing strategies for virtualization-based distributed environments must fulfill the following requirements: 1. Support for service level management 2. Separation of control algorithms from the management framework 3. Support for different virtualization technologies 4. Support for a common evaluation mechanism 5. Scalability (1) means that the framework should provide support for managing services hosted in virtual machines. This involves monitoring various QoS parameters and making sure that these parameters conform to a certain Service Level Objective (O). (2) basically assures that the management framework is responsible for dealing with aspects like monitoring and execution of tasks, while a separate intelligent controller defines management tasks based on gathered monitoring data. As such, a framework should support different types of intelligent controllers by providing a generic controller interface. (3) requires the framework to support different virtualization technologies (e.g. ware ESX or Xen), transparently for the controller. Thus, from a controller s perspective, the framework is acting as an abstraction layer on top of the virtualization technology. Generic interfaces for monitoring and task execution should simplify plugging in adapters for various virtualization technologies.

3 Cluster Manager requests/alarms Cluster requests/alarms Manager Manager Manager Manager Physical Manager Physical Manager As As As As M M 1!""""""""""# 1!""""""""""$ 1!""""""""""% Cluster of physical machines - Service Figure 1. The architecture of the framework (4) means that the framework has to support a consistent mechanism for tracing and comparing management decisions. Only this way different self-management approaches can be evaluated against each other. (5) states that the framework should be scalable with respect to the number of physical and virtual machines that it can manage. New physical or virtual machines dynamically added to the cluster must be recognized by the framework. Figure 1 depicts the design of our framework with respect to the requirements discussed above. The framework is used to manage a cluster of n physical machines, each hosting a number between 0 and m virtual machines. Each virtual machine has a Manager, each physical machine has a Physical Manager and the entire cluster is managed by one Cluster Manager. The Physical Manager is the simplest component of the framework. It s job is to monitor the resource utilization of the physical machine through its module. Besides monitoring, the Physical Manager also executes commands coming from the Cluster Manager through its module. Both the and the modules monitor respectively control the physical machine through the M. The Manager monitors parameters like CPU utilization and available memory with respect to the virtual machine through the module. It also monitors the service/application running inside the virtual machine through the module. We assume that each virtual machine hosts only one service, e.g. a web server, a mail server or a database; we argue that this is common practice in a server consolidation scenario. The two monitors feed the gathered data to the module, which uses this data to determine whether the service is running at the required parameters. If this is not the case, the tries to determine which of the s resource is the bottleneck (i.e. memory, CPU, etc.). When such a bottleneck is determined, the Manager uses the module to request a larger amount of the resource that causes the bottleneck from the Cluster Manager (i.e. request more memory, a larger CPU share etc.). The Cluster Manager has a global view of both available and allocated resources, generated using the data gathered from the Physical Managers. The Cluster module uses this global view to determine how requests from the Manager can be fulfilled. Thus, the Cluster module is actually what we previously referred to as the intelligent controller. After a decision has been taken, the Cluster Manager dictates commands to the Physical Manager(s) through its module. It can be easily observed that this framework fulfills the previously defined requirements. First, the way that the Manager is designed specifically addresses the service running in the managed virtual machine. Various Cluster components that use different self-management strategies can be easily plugged into the framework. Furthermore, different virtualization technologies can be addressed by simply developing the necessary adapters for each virtualization technology. It is possible to use stan-

4 TPC-W Load Generator Physical Machine Manager Manager Physical Manager Physical Manager TPC-W Web App Tomcat Virtual Machine Physical Machine Physical Machine Figure 2. The testbed dard benchmarking tools to generate load for the services running inside the virtual machines and then use the component to evaluate how these services are performing. This way, different intelligent controllers can be evaluated with respect to how the services are performing under various loads. Last, adding new physical and virtual machines to the cluster can be done by simply registering with the cluster manager. 4. Implementation We have implemented a prototype of the framework in Java using Xen as the virtualization technology. Our prototype implementation is based on the Self Manager Core that has been developed in the Distributed Systems Lab of Wiesbaden University of Applied Sciences [15, 14]. The Manager uses JMX [5] to monitor the parameters of a Xenbased virtual machine (the component) and the response times of an Apache Tomcat server running inside the virtual machine (the component). The is implemented as an expert system and uses the data from the and the to feed Jess [13], a rule engine. The rule engine matches the data against a rule set. We have developed a basic set of rules, which is used by Jess to determine the bottlenecked resource when the response times of the service are higher than a given threshold. For the Physical Manager, an adapter has been implemented that uses the Xen-API [22] to manage Xenbased physical machines. This involves both monitoring and dynamically allocating resources. Both the Manager and the Physical Manager communicate with the Cluster Manager using Java RMI. The Cluster Manager provides support for plugging-in different Cluster components through a messaging interface. More implementation details can be found in [7]. We have tested the framework in a lab environment using a Java implementation of the TPC-W benchmarking standard [17]. This testbed can be observed in Figure 2. The TPC-W e-commerce application suite is hosted inside a Tomcat server running on top of a virtual machine managed by the Manager. Two physical machines are managed by two different Physical Managers, with one of them hosting the virtual machine. The two Physical Managers, the Manager and the Cluster Manager are hosted on a third physical machine, which also hosts the TPC-W load generator. This machine is not part of the under-management cluster. When the TPC-W load generator is started, the Manager is able to observe a dramatic increase in the response times of the Tomcat service and determines the memory as being the bottleneck. After more memory is given, the response times of the Tomcat service decrease up to an acceptable level. This behaviour is shown in Figure 3 and proves that the Manager is able to successfully determine the resource causing the bottleneck. Distributed

5 Influence of Memory Allocation on Service Response Time , Bytes ,5 1 O Violations OS Free Memory OS used Swap ,5 Measured O Violations per Minute 0 0 0:00:00 0:00:20 0:00:42 0:01:02 0:01:22 0:01:42 0:02:02 0:02:22 0:02:42 0:03:02 0:03:22 Time (s) Figure 3. Influence of available memory on O violations tests including migrating a on a secong physical machine when necessary are currently underway. 5. Conclusion and outlook In this paper, we have argued that virtualization-based environments are an important application area for autonomic computing, but still in its infancy at the moment. Furthermore, it is hard to objectively evaluate the currently published autonomic computing approaches for virtualizationbased environments. The main contribution of this paper is the design of a framework for developing and evaluating autonomic computing strategies for virtualization-based environments. Using this framework, different controller strategies can be easily developed, plugged-in and evaluated against each other. Our framework is not virtualization technology-bound, instead adapters for various virtualization technologies can be easily developed and plugged into the framework. We are currently working on different approaches for an intelligent controller. We have discovered that our resource allocation problem belongs to the family of knapsack problems. Knapsack problems are known to be NP-hard. This means that we are dealing with an NP-hard optimization problem. This is an important discovery, since it is commonly believed that, for NP-hard optimization problems, no algorithm exists that finds an optimal solution in polynomial time. As such, for our resource allocation problem, we can either use heuristics or approximation algorithms. While for the moment we are working on two different heuristicbased algorithms, in the future we plan to design an intelligent controller that uses an approximation algorithm and thus has a guaranteed performance ratio. Details about the design and evaluation of these controllers as a Cluster component in our framework will be made available in a future publication. References [1] N. Bobroff, A. Kochut, and K. Beaty. Dynamic placement of virtual machines for managing sla violations. In Integrated Network Management, IM th IFIP/IEEE International Symposium on, pages , [2] C. Clark, K. Fraser, S. Hand, J. G. Hansen, E. Jul, C. Limpach, I. Pratt, and A. Warfield. Live migration of virtual machines. In Proceedings of the 2nd ACM/USENIX Symposium on Networked Systems Design and Implementation (NSDI), pages , Boston, MA, May [3] M. Debusmann, M. Schmid, and R. Kroeger. Model-Driven Self-Management of Legacy Applications. In L. Kutvonen and N. Alonistioti, editors, 5th IFIP International Conference on Distributed Applications and Interoperable Systems (DAIS 2005), Athens, Greece, June 2005, pages IFIP, Springer, June [4] L. Grit, D. Irwin, A. Yumerefendi, and J. Chase. Virtual machine hosting for networked clusters: Building the foundations for autonomic orchestration.

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