André Moreira

A case for virtualization of content delivery networks

Content Delivery Networks have gained a popular role among application service providers (ASPs) and infrastructural companies. A CDN is an overlay network that gives more control of asset delivery by strategically placing servers closer to the end-user, reducing response time and network congestion. Many strategies have been proposed to deal with aspects inherent to the CDN distribution model. Though mostly very effective, a traditional CDN approach of statically positioned elements often fails to meet quality of experience (QoE) requirements when network conditions suddenly change. In this paper, we introduce the idea of CDN virtualization. The goal is to allow programmatically modification in CDN infrastructure designed for video distribution, adapting it to new operating conditions. We developed a complete simulator focused on CDN overlay network characteristics where we implemented several approaches for each of the CDN elements. Our results show a decrease of 20% in startup delay and network usage.

Highly Available Clouds: System Modeling, Evaluations, and Open Challenges

Cloud-based solution adoption is becoming an indispensable strategy for enterprises, since it brings many advantages, such as low cost. On the other hand, to attend this demand, cloud providers are facing a great challenge regarding their resource management: how to provide services with high availability relying on finite computational resources and limited physical infrastructure? Understanding the components and operations of cloud data center is a key point to manage resources in an optimal way and to estimate how physical and logical failures can impact on users’ perception. This book chapter aims to explore computational modeling theories in order to represent a cloud infrastructure focusing on how to estimate and model cloud availability.

Prototyping a high availability PaaS: Performance analysis and lessons learned

With cloud computing consolidation, Platform-as-a-Service (PaaS) has been used as a solution for developing applications with low cost and maximum flexibility. However, an open challenge related to PaaS is the proper handling of multi-tier and stateful applications with support for high availability (HA); and scalability can be considered an essential feature for HA. However, dealing with several instances of the same application that access its state in a common area is not a simple task. This paper presents a novel PaaS framework, named NoPaaS, that supports the deployment of multi-tier and stateful applications assuring their availability according to the Service Availability Forum (SAF) redundancy model. The primary goal of this work is to present NoPaaS framework and prototype, and highlight challenges and open issues when providing multi-tier and stateful applications in high availability clouds.

Minimizing and Managing Cloud Failures

Guaranteeing high levels of availability is a huge challenge for cloud providers. The authors look at the causes of cloud failures and recommend ways to prevent them and to minimize their effects when they occur.

An adaptable storage slicing algorithm for content delivery networks

Several works study the performance of Content Delivery Networks (CDNs) under various network infrastructure and demand conditions. Some go even further while considering demand elasticity by leveraging on Cloud elasticity where each Content Service Provider (CSP) is served only the amount of storage space and network throughput that it needs and pays accordingly. Many of todays CDN implementations are based on these proposals. However, the allocation of virtual servers in cloud computing is not yet very fine-grained and suffers from limitations and time constraints for reallocation. This work proposes an efficient cache slicing mechanism that frees the CDN provider from dedicating a different virtual surrogate for each CSP in each location. This is achieved by dealing internally with the allocation space for each CSP in a shared surrogate, while still providing services in terms of network storage allowing a CSP to select and pay the amount of content that can be stored. We show that the proposed approach deals better with peak surrogate usage, and reduces the total network traffic by around 15% and cross-traffic by as much as 35% under some scenarios.

Analyzing strategies to effectively detect changes in content delivery networks

Content Delivery Networks have gained a popular role among application service providers (ASPs) and infrastructural companies. A CDN is an overlay network that gives more control of asset delivery by strategically placing servers closer to the enduser, reducing response time and network congestion. Many strategies have been proposed to deal with aspects inherent to the CDN distribution model. Though mostly very effective, a traditional CDN approach of statically positioned elements often fails to meet quality of experience (QoE) requirements when network conditions suddenly change. In this paper, we introduce a technique to detect significant changes in a monitored metric of a CDN in order to allow provisioning adaptation of resources, using easy access information with great practical viability. Results show decrease on network resources usage without considerable changes on quality of service (QoS). Furthermore, our technique has similar performance in comparison to an omniscient strategy.