Ajay Mohindra

Dynamic Scaling of Web Applications in a Virtualized Cloud Computing Environment

Scalability is critical to the success of many enterprises currently involved in doing business on the web and in providing information that may vary drastically from one time to another. Maintaining sufficient resources just to meet peak requirements can be costly. Cloud computing provides a powerful computing model that allows users to access resources on-demand. In this paper, we will describe a novel architecture for the dynamic scaling of web applications based on thresholds in a virtualized Cloud Computing environment. We will illustrate our scaling approach with a front-end load-balancer for routing and balancing user requests to web applications deployed on web servers installed in virtual machine instances. A dynamic scaling algorithm for automated provisioning of virtual machine resources based on threshold number of active sessions will be introduced. The on-demand capability of the Cloud to rapidly provision and dynamically allocate resources to users will be discussed. Our work has demonstrated the compelling benefits of the Cloud which is capable of handling sudden load surges, delivering IT resources on-demands to users, and maintaining higher resource utilization, thus reducing infrastructure and management costs.

Autonomic personal computing

Autonomic personal computing is personal computing on autonomic computing platforms. Its goals combine those of personal computing with those of autonomic computing. The challenge of personal autonomic computing is to simplify and enhance the end-user experience, delighting the user by anticipating his or her needs in the face of a complex, dynamic, and uncertain environment. In this paper we identify the key technologies that enable autonomic behavior as distinguished from fault-tolerant behavior. We give some examples of current autonomic behavior and some general considerations for an architecture that supports autonomic personal computing. We identify its challenges to standards and technology developers and conclude with some guidance for future work.

Resource Calculations with Constraints, and Placement of Tenants and Instances for Multi-tenant SaaS Applications

Cost of customization, deployment and operation of a software application supporting multiple tenants can be lowered through multi-tenancy in a new application business model called Software as a Service (SaaS). However, there are a number of technical challenges that need to be tackled before these benefits can be realized. These challenges include calculations of resource requirements for multi-tenants with applied constraints in a shared application instance, the optimal placement of tenants and instances with maximum cost savings but without violating any requirements of service level agreements for all tenants in a set of servers. Moreover, previously reported capacity planning and resource allocation methods and tools are not tenant aware. This paper will address and provide novel solutions to these challenges. We also describe the first of a kind, a multi-tenant placement tool for application deployment in a distributed computing environment.

Recovery in the Calypso file system

This article presents the deign and implementation of the recovery scheme in Calypso. Calypso is a cluster-optimized, distributed file system for UNIX clusters. As in Sprite and AFS, Calypso servers are stateful and scale well to a large number of clients. The recovery scheme in Calypso is nondisruptive, meaning that open files remain open, client modified data are saved, and in-flight operations are properly handled across server recover. The scheme uses distributed state amount the clients to reconstruct the server state on a backup node if disks are multiported or on the rebooted server node. It guarantees data consistency during recovery and provides congestion control. Measurements show that the state reconstruction can be quite fast: for example, in a 32-node cluster, when an average node contains state for about 420 files, the reconstruction time is about 3.3 seconds. However, the time to update a file system after a failure can be a major factor in the overall recovery time, even when using journaling techniques.

Solution-based deployment of complex application services on a Cloud

Managing and containing runaway IT costs for solution deployment is one of the top priorities for enterprises. Cloud Computing, with its on-demand provisioning capability on shared resources, has emerged as a new paradigm for reducing IT costs. In this paper, we describe a solution-based provisioning mechanism to automate the deployment of complex application services on a Cloud infrastructure. We introduce the concept of Composite Appliance and show how it can be used to deploy a complete solution and to simplify management tasks. We illustrate the advantages of our approach with a prototype solution consisting of two-tier application services that are deployed and configured automatically on virtual machine instances without manual intervention.

Exploiting non-determinism for reliability of mobile agent systems

An important technical hurdle blocking the adoption of mobile agent technology is the lack of reliability. Designing a reliable mobile agent system is especially challenging since a mobile agent is potentially affected by failure of any host that it visits, or failure of any communication link that it needs to traverse. Previous work in this domain has attempted techniques such as periodic checkpointing of mobile agent state and restarting upon machine or communication recovery. Such approaches render an agent unavailable until a machine or a communication link itself recovers. In this paper, we take an alternate approach based on the premise that a mobile agent can often complete its task in more than one way. We capture such redundancy in non-deterministic constructs in the agent language and maintain state about an agents actual computational path in its possible computational tree. We design and implement a distributed recovery scheme that detects a failure, rolls back an agents computation, and restarts the agent from a previous point in its computational tree down a different but equivalent computational path without waiting for the actual failure itself to be repaired.

Enterprise data access from mobile computers: an end-to-end story

Currently, hand-held and palmtop computers are widely used for personal information management. In the near future, they will also be used to access enterprise data. There are however, numerous technical challenges in enabling an end-to-end system that provides enterprise data access from mobile computers. The challenges include heterogeneity, various resource constraints, scalability and security. In this paper, we describe the design and implementation of the Mobile Data Synchronization Service (MDSS), an end-to-end system that provides enterprise data access from mobile computers. Specifically, we address the heterogeneity of devices and data sources, the memory and power constraints of devices, the poor quality of communication and the need for scalability. Our system achieves interoperability and solves the key technical challenges related to enterprise data access from mobile computers.

Scalability and Performance of Web Applications in a Compute Cloud

Scalability and performance are key factors to the success of many enterprises involved in doing business on the web. Maintaining sufficient web resources just to meet performance during peak demands can be costly. Compute Cloud provides a powerful environment to allow dynamic scaling of web applications without the needs for user intervention. In this paper, we present a case study on the scalability and performance of web applications in a Cloud. We describe a novel dynamic scaling architecture with a front-end load-balancer for routing user requests to web applications deployed on virtual machine instances with the goal of maximizing resource utilization in instances while minimizing total number of instances. A scaling algorithm for automated provisioning of virtual resources based on threshold number of active user sessions will be introduced. The on-demand capability of the Cloud to rapidly provision and dynamically allocate resources to users will be discussed. Our work has demonstrated the compelling benefits of a Cloud which is capable of sustaining performance upon sudden load surges, delivering satisfactory IT resources on-demands to users, and maintaining high resource utilization, thus reducing infrastructure and management costs.

Distributed token management in Calypso file system

This paper presents the design and implementation of a distributed token manager for a cluster-optimized, distributed Unix file system. In this file system, tokens provide cache consistency and support for single-system Unix semantics. The paper describes the token types used, token arbitration protocol, deadlock-free implementation, fault-tolerance, and recovery. The key contributions of the work reported here are: (1) An efficient protocol for token arbitration, which minimizes bottlenecks and hence enhances scalability; (2) A practical approach to handling deadlocks, race conditions, and recovery issues, which complicate token manager design and implementation.<<ETX>>

Reducing Complexity of Software Deployment with Delta Configuration

Deploying a modern software service usually involves installing several software components, and configuring these components properly to realize the complex interdependencies between them. This process, which accounts for a significant portion of information technology (IT) cost, is complex and error-prone. In this paper, we propose delta configuration - an approach that reduces the cost of software deployment by eliminating a large number of choices on parameter values that administrators have to make during deployment. In delta configuration, the complex software stack of a distributed service is first installed and tested in a test environment. The resulting software images are then captured and used for deployment in production environments. To deploy a software service, we only need to copy these pre-configured software images into a production environment and modify them to account for the difference between the test environment and a production environment. We have implemented a prototype system that achieves software deployment using delta configuration of the configuration state captured inside virtual machines. We perform a case study to demonstrate that our scheme leads to substantial reduction in complexity for the customer, over the traditional software deployment method.