18 Published by the IEEE Computer Society 1089-7801/13/$31.00 2013 IEEE IEEE INTERNET COMPUTING

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Key Challenges in Cloud ComputingEnabling the Future Internet of Services

Rafael Moreno-Vozmediano, Rubn S. Montero, and Ignacio M. LlorenteComplutense University of Madrid

Cloud computing will play a major role in the future Internet of Services,

enabling on-demand provisioning of applications, platforms, and computing

infrastructures. However, the cloud community must address several

technology challenges to turn this vision into reality. Specific issues relate

to deploying future infrastructure-as-a-service clouds and include efficiently

managing such clouds to deliver scalable and elastic service platforms on

demand, developing cloud aggregation architectures and technologies

that let cloud providers collaborate and interoperate, and improving cloud

infrastructures security, reliability, and energy efficiency.

T he Cross-European Technology Platforms (X-ETPs) Group envisions the Internet of Services (IoS) as a key pillar of the future Internet (see Figure 1).1 The IoSs main goal is to present everything on the Internet as a service, includ-ing software applications, platforms for developing and delivering these appli-cations, and underlying infrastructures (CPUs, storage, networks, and so on). In this scenario, cloud technology can play an important role in enabling IoS deploy-ment because it comprises different pro-visioning models for on-demand access to applications (software as a service, or SaaS), platforms on which developers can build services and applications (platform as a service, or PaaS), and elastic com-puting infrastructures (infrastructure as a service, or IaaS).

Using these cloud technologies to support the IoS has several benefits:

service elasticity resulting from clouds ability to automatically scale services and infrastructures;

cost reduction when infrastructure and platform sizes are adapted to service demands;

pay-per-use models that let users pay only for actual resource consumption;

improved time-to-market for services owing to reduced development and infrastructure deployment times;

increased service availability and reli-ability resulting from the replication of service components and rapid deploy-ment of new service instances; and

cloud interoperability, which lets users deploy a service on multiple

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clouds, thus providing unlimited scalability and optimized service performance.

The current cloud market includes all three aforementioned cloud models, but infrastruc-ture clouds are the foundation of the future IoS (see Figure 2). As such, advances in IaaS cloud computing should address the challenges in herent to meeting the future Internets require-ments by providing new tools and capabilities that let users deploy and manage their own multi-tier applications and development platforms.

Several papers in the literature have ana-lyzed cloud computing challenges for exam-ple, one study ranks the technical obstacles to cloud computings adoption and growth, and describes corresponding research and develop-ment opportunities.2 Another survey identi-fies various design challenges and important research directions in this area.3 Some lines of research in cloud computing analyze the cost of cloud service data centers and propose some improvements in cloud management to opti-mize investment.4 Another study analyzes the main features of a cloud computing system and compares it to grid technology.5

Here, we analyze the main research and technological challenges that the cloud com-munity must tackle to unleash IaaS clouds full potential and enable future IoS deployment. Although we revisit some issues that these pre-vious studies have addressed, we also present these challenges from a new IoS requirement perspective. The cloud platforms we consider can range from private, on-premise cloud infra-structures to large, public IaaS providers to hybrid cloud infrastructures.

Future IoS RequirementsThe X-ETP Groups Future Internet Research Agenda analyzes the main topics and issues the research community must address to provide the technological foundations for the future IoS.1 According to this analysis, requirements should cover both provisioning and deploy-ing dynamic services in a single infrastruc-ture provider as well as deploying services across different infrastructure providers. Other requirements, which we discuss later, are cross-cutting challenges that cover the future Inter-nets four different pillars. We also looked at a study that identifies some additional require-ments for the systems that will support the

future IoS.6 Weve compiled the most important challenges that next-generation IaaS cloud pro-viders must address to fulfill these IoS require-ments and analyze their current state and future directions.

Single Infrastructure ProvidersIn the future Internet, IaaS cloud providers should be able to deliver scalable, on-demand infrastructures (including network, compute, and storage elements) that satisfy the require-ments for different types of elastic services and workloads. In particular, single infrastruc-ture providers must support dynamic service provisioning;1,6 quality-of-service (QoS)1 and service-level agreement (SLA) negotiation;6 service scalability;1 service monitoring, billing, and payment;6 and context-aware services.1

Dynamic service provisioning. To provide effi-cient service virtualization, cloud platforms should decouple the service interface from the implementation in a way that enables ser-vice providers to map services dynamically to resources.1 Although SaaS clouds provide access to applications on demand, and PaaS clouds let users develop and execute applica-tions on specific platforms, IaaS clouds let users build their own customized applications and platforms without being tied to a specific envi-ronment (such as an operating system, platform technology, or software library). However, most current IaaS clouds are too infrastructure- oriented. They lack the advanced service-oriented capabilities needed to manage services (that is, groups of interconnected compute, network, and storage elements) as basic entities or provide

Figure 1. Pillars of the future Internet. The Cross-European Technology Platforms document defines the main vectors (four pillars) of growth for the future Internet and provides a comprehensive collection of active and upcoming developments in the future Internet research world.

Future network society

Future network infrastructure

Internet byand for the

people

Internet ofcontent andknowledge

Internet ofThings

Internet ofServices

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20 www.computer.org/internet/ IEEE INTERNET COMPUTING

elasticity and QoS for a broad range of multi-t ier appl icat ions deployed in the c loud. Therefore, the ability to efficiently deploy and manage these applications in the cloud still requires complex IT scenarios and skilled tech-nology staff.

Future directions and research lines in this area should aim to enable the dynamic provi-sioning of multitier services on top of cloud infrastructures. Hence, next-generation IaaS clouds should incorporate several new service- oriented features: functionality that can man-age a services entire life cycle (including deployment, runtime scaling, and termination); different mechanisms and policies for service admission control (that is, decision-making ability regarding accepting or rejecting a ser-vice); service-level monitoring capabilities to control how service constraints, SLAs, and elasticity rules are fulfilled; SLA management functionality to guarantee a services perfor-mance and reliability; and service elasticity management capabilities to guarantee that the service can scale automatically.

QoS and SLA negotiation. Cloud computing platforms should support standardized ser-vice expressions for QoS1 and SLA negotiation

mechanisms between consumers and providers that state the terms under which the service is to be provided.6 Most current IaaS platforms offer simple SLAs based on resource availabil-ity, but lack advanced SLA mechanisms that are based on service-oriented QoS metrics, such as performance, availability, response time, and service cost. Moreover, because cloud providers offer different SLA types, defined with various service-level objectives (SLOs) and QoS met-rics, its difficult for users to negotiate similar SLAs with different cloud providers, which can become an obstacle to expanding aggregated cloud infrastructures.

Future directions include defining a stan-dard set of SLA levels that all cloud providers can agree on and commit to fulfill. Each SLA level should be defined via a well-known, rich set of SLOs and service-oriented QoS metrics. An interesting initiative in this area is the Web Services Agreement Specif ication from the Open Grid Forums Grid Resource Allocation Agreement Protocol (GRAAP) working group (https://forge.ogf.org/sf/projects/graap-wg). This specification defines a language and pro-tocol for defining and negotiating SLAs in dis-tributed systems, such as grids and clouds.

Service scalability. Although many services can be static from a capacity or size viewpoint, in general, services can experience f luctuat-ing workloads. Variable workloads require that the service capacity adapt to demand to avoid performance degradation (in cases of increas-ing demand) or oversizing (in cases of lowering demand). Cloud providers can attain optimal service provisioning if they offer elasticity management and auto-scaling tools. Some cur-rent IaaS cloud providers such as Amazon Elastic Compute Cloud (EC2; http://aws.amazon .com/ec2) and RightScale (www.rightscale.com) offer simple mechanisms that auto-scale groups of instances based on alert mechanisms that trigger the deployment of new instances when some condition is met. These mechanisms are based mainly on infrastructure metrics (CPU load, bandwidth consumption, and so on) and are usually reactive that is, the infrastructure reacts to changes in the metrics.

Future lines of research should be oriented toward improving cloud providers techniques for service auto-scaling. In this context, pro-viders could define more complex elasticity

Figure 2. Cloud computing model for the future Internet of Services (IoS). Cloud technology enables the future IoS, and the infrastructure-as-a-service clouds represent this models foundation.

Software as a service(on-demand access to any application)

Platform as a service(platform for building and deliveringapplications)

Infrastructure as a service(on-demand compute/network/storage infrastructures)

Virtual/physical infrastructure

Internetof Services

Servers Networks Storage

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rules based on different metrics (including both infrastructure-level and QoS metrics); analyze correlations between infrastructure and QoS metrics for different service types and work-load profiles to implement efficient auto-scaling mechanisms when lacking service metrics; and implement proactive auto-scaling mechanisms based on service load prediction to make scal-ing decisions ahead of time.

Service monitoring, billing, and payment. Most common billing mechanisms that current IaaS cloud providers offer are based on each users individual resource consumption per t ime unit (for example, the number of used com-pute instances, the total Mbytes transferred, or the total amount of storage capacity used).7 Accounting and monitoring mechanisms are key aspects of cloud platform management when these billing strategies are implemented. The accounting objective is to obtain and record resource usage information (CPU, memory, disk, bandwidth, and so on) so that billing mecha-nisms can produce billing information, typi-cally on a per-user basis. Accounting relies on monitoring mechanisms that collect information about the state of cloud resources using various sensors, each responsible for a different aspect of the system being monitored (such as CPU load, memory usage, running processes, disk usage, and power or bandwidth consumption).

Future directions in monitoring, billing, and payment aim at adapting these mechanisms to a service-oriented framework, so that billing and payment can occur on a per-service basis rather than via the traditional per-user scheme. Accounting mechanisms should also adapt to produce per-service billing information by con-sidering the resources each particular service consumes per time unit and different resource prices, pricing models, and so on. In this sce-nario, cloud providers could offer special pricing plans, discounts, or flat fees for those services that guarantee a minimum consumption in terms of compute instances, data transfers, and storage capacity over a given time period.

Context-aware applications. A key challenge the future IoS must address is the increase in relevancy of information in a given context.1 Such context awareness is becoming essen-tial in many applications and services, such as mobile applications, social networks, and

pervasive computing environments. Context-aware applications adapt their behavior to the environment for example, location, user activity, people nearby, or accessible devices.

To support context-aware applications, cloud platforms should provide new services that can collect context information, perform context analysis, manage data privacy, and support applications requesting context information. In addition, IaaS cloud platforms should also pro-vide context-aware provisioning mechanisms for example, letting users select the region or country where a service is going to be deployed to meet geographic location restrictions (to avoid legal issues, guarantee the services prox-imity to a given group of people or a specific service, and so on). These location restrictions could force providers to allocate a service to a specific region, or could prevent a services dis-tribution across multiple clouds.

Aggregating Infrastructure ProvidersTwo key technological challenges for the future IoS are supporting the deployment of distrib-uted services across different IaaS providers and enabling the portability of such services.1 These challenges require research on architec-tures and brokering mechanisms for aggregat-ing cloud providers and defining standards for cloud interoperability and portability.

Service deployment across different providers. Current IaaS cloud technologies support two main aggregation architectures: cloud-bursting and cloud-brokering models. The cloud-bursting architecture, also known as the hybrid cloud, combines exist ing, on-premise cloud infra-structures with remote resources from one or more public clouds to provide extra capacity and satisfy peak demand periods. The cloud-brokering architecture uses a broker8 to serve as an intermediary between users and provid-ers. It helps users choose the most suitable cloud on which to deploy their services, and even lets users deploy different service components across multiple clouds. These two architectures exhibit many similarities in terms of the cou-pling degree among cloud instances involved; both correspond to loosely coupled scenarios that is, a cloud provider has little or no control over remote resources, monitoring information about remote resources is limited, and no cross-site features are supported.

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In this context, one open research line is to develop novel aggregation architectures that allow a higher degree of coupling in which a provider could

have advanced control over remote resources (such as decision-making about where a remote instance is placed);

access detailed monitoring information about remote resources; and

implement some advanced cross-site fea-tures (for example, cross-site hot migra-tion of cloud instances, or the creation of cross-site virtual networks or virtual storage systems).

As regards cloud-broker architectures, another open research line is to integrate different placement algorithms and policies for optimal service deployment based on different optimi-zation criteria (cost optimization, performance optimization, energy efficiency, proximity, high availability, and so on). These policies facilitate automatic decision-making about how to select the best cloud to deploy a service, optimally distr ibute a services different components among different clouds, or even when to move a given service component from one cloud to another to satisfy some specific optimization criteria.

Interoperability and portability. Service por-tability between different cloud providers involves several challenges due to a lack of standard interfaces for interacting with differ-ent clouds and standard interfaces and formats for managing virtual appliances. Currently, no standard way exists for interfacing with a cloud, and each provider exposes its own APIs. Clearly, cloud providers must unify their differ-ent cloud APIs and adopt a standardized cloud interface. In this context, several efforts are under way, such as

the Open Cloud Computing Interface (OCCI; http://occi-wg.org), which defines a protocol and API specification for remotely manag-ing cloud computing infrastructures;

the Cloud Infrastructure Management Inter-face (CIMI; http://dmtf.org/standards/cloud), a work-in-progress standard that defines an interface and a logical model for managing resources within an IaaS cloud; and

the Cloud Data Management Interface (CDMI; www.snia.org/cdmi), which defines an inter-face that applications can use to create, retrieve, update, and delete data elements from the cloud.

Another important obstacle for users who decide to move their services from one cloud to another is a lack of compatibility in image-packaging formats and image-management interfaces. Some standardization efforts also exist in this area, such as the Open Virtualization Format (OVF; www.dmtf.org/standards/ovf), which defines a standard for packaging and distributing virtual appliances.

Some IaaS platforms, such as OpenNebula (ht tp://opennebula.org), Eucalyptus (www .eucalyptus.com), and OpenStack (www.openstack .org), have made important contributions in the deployment of interoperable cloud platforms by incorporating different, well-known interfaces. For example, OpenNebula implements de jure standard specifications such as OCCI, CDMI, and OVF to enable interoperability among cloud platforms, whereas Eucalyptus and OpenStack have built their interoperable solutions using Amazon Web Services (AWS; http://aws.amazon .com) as a de facto standard.

The main open issues and future directions in portability and interoperability include com-pleting the ongoing cloud standards and get-ting cloud providers and vendors to adopt them, allowing for full interoperability between dif-ferent cloud platforms.

Additional Cross-Cutting ChallengesThe X-ETP Groups Future Internet Research Agenda also identifies several issues that cover the future Internets four different pillars. Some of these issues are also key aspects in the devel-opment of next-generation IaaS clouds.

Security, Privacy, and TrustSecurity, privacy, and trust form a cross- discipline that must be included in all aspects of the future Internets design.1 Although cloud platforms and providers incorporate different mechanisms and technologies to guarantee the security and privacy of users data and resources, significant potential for improvement exists regarding the authentication, authoriza-tion, and auditing mechanisms implemented in current IaaS clouds.9

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Authentication mechanisms verify and con-firm the identity of users who try to access cloud resources. Many cloud providers use weak, password-based authentication; this could be improved with trusted authentication mecha-nisms based on public keys, X.509 certificates, or the Lightweight Directory Access Protocol (LDAP).

Authorization policies control and manage users privileges and permissions to access dif-ferent cloud resources (compute resources, net-works, storage, and data), and are essential to guarantee data protection and resource isolation in a multitenant cloud environment. Most cur-rent cloud platforms use authorization mecha-nisms based on user access control, meaning they define access policies for each individual user (for example, quota mechanisms that limit the amount of resources that a specific user can use). However, because cloud platforms can have thousands of users and resources, specifying policies for user groups with similar functional-ities would be more practical for example, by incorporating role-based access control mecha-nisms and supporting multiple roles for differ-ent types of users and administrators.

Auditing mechanisms aim at providing information about activity on cloud resources and identifying who is accessing them, when theyre gaining access, and what operations theyre doing. According to the Distributed Management Task Forces Cloud Auditing Data Federation (CADF) working group (http://dmtf .org/standards/cloud), cloud providers should be able to provide specific audit event, log, and report information on a per-user basis, as well as standard mechanisms for their users to self-audit application security that includes information about the hardware, software, and network infrastructure the provider uses to run specific user applications.

Cloud interoperation also opens new chal-lenges in managing secur it y parameter s between cloud providers. One of the first issues that should be solved is authentication across multiple clouds, given that each cloud can use a particular authentication mechanism and technology. Some methods, such as the single sign-on (SSO) technology, enable providers to define federated identities that they can share securely across different sites. Regarding data protection, confidentiality, and privacy issues, the movement of resources and data between

cloud providers can be limited by the different laws in the countries where cloud providers are located. To avoid privacy and confidentiality risks, cloud providers should be able to adapt to different legislation, and the cloud community should define some standards for good prac-tices, policies, and procedures. In this regard, the European Network and Information Secu-rity Agency (ENISA)10 and the US National Institute of Standards and Technology (NIST)11 have issued some interesting security recom-mendations and guidelines.

Future directions for addressing security in cloud infrastructures include improving authentication mechanisms at the individual cloud level (for instance, trusted authentication) and across multiple clouds; improving authori-zation and access control mechanisms (such as role-based access control and multiple-role sup-port); developing standard mechanisms, data models, and APIs for cloud auditing and self-auditing of user services; and defining security standards that comply with various recom-mendations and legislation, including differ-ent security levels adapted to different service security requirements.

Availability, Reliability, and ResiliencyAn important aspect that characterizes Inter-net services is availability, measured in terms of average service availability over a given time period.1 Two factors that affect availabil-ity are reliability (the probability that a system fails within a given time period) and resil-iency (a systems ability to reach and maintain an acceptable level of service when faced with various faults and challenges to normal opera-tion). Incorporating different techniques to improve the availability, reliability, and resil-iency of services deployed in cloud infrastruc-tures is essential to supporting the future IoS. Some existing IaaS cloud platforms have intro-duced various features to provide high avail-ability and failover functionality at the virtual machine (VM) level (for example, by detecting VM crashes and automatically restarting the VM) and the physical server level (for instance, by detecting server hardware failures and re deploying all the VMs on another server).12

Future research efforts should be oriented at implementing advanced techniques to ensure availability at both the service and cloud levels. Providers could implement availability on

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a per-service basis by monitoring the differ-ent service components and setting policies for automatic redeployment of service instances in case of VM, physical server, or network failure. In addition, the support for hybrid and multi-zone cloud deployments should let providers replicate service components in different sites, enabling the configuration of design for fail-ure applications that can continue execution and recover even if a complete site fails. Regard-ing availability at the cloud level, support for high-availability architectures with persistent database back-end and high-availability con-figurations can help preserve the clouds state in the event of a hardware or software failure.

Energy EfficiencyIT companies must meet global and national goals for carbon-footprint reduction, and must compensate for noticeable increases in energy expenditures; thus, technological energy-saving measures are a mandatory ingredient for any emerging information and communication technology.1 In this context, IaaS cloud provid-ers must evaluate and assess different strategies to improve energy efficiency in their data cen-ters, including computing, cooling, and power supply equipment. This involves defining and using unified metrics, such as the power usage effectiveness (PUE) or data center infrastructure efficiency (DCIE) metrics,13 among others. These help cloud providers measure their data centers energy efficiency, compare the results against other cloud infrastructures, and decide what improvements are necessary.

Some open issues include developing more efficient energy-proportional servers14 that con-sume power proportionally to utilization level; and improving cloud resource allocation, con-solidation, and migration strategies that consider each particular services workload profile. For example, the reallocation of service components for consolidating purposes can be efficient from a power-saving perspective, but can be counter-productive for service performance when workloads have tightly coupled communica-tions requirements. Another future direction is to research mechanisms for advanced resource provisioning, based on a services historical execution profile, to predict the resources that the service will consume, allowing for opti-mal provisioning that results in lower energy consumption.

C loud computing could become a major player in the deployment of the future IoS. At pres-ent were at the starting gate, and must address many research and technology challenges and overcome several adoption barriers. Fortu-nately, cloud solution architectures include technology components from different fields, and many of these cloud computing challenges have already been addressed to a certain degree by various research communities, mostly virtu-alization, grid, and autonomic computing. These challenges will play a decisive role in defining the technology roadmap for developing future IaaS cloud platforms.

AcknowledgmentsThis research was partially supported by Consejera de

Educacin of Comunidad de Madrid, Fondo Europeo de

Desarrollo Regional (FEDER), and Fondo Social Europeo

(FSE) through MediaNet Research Program S2009/TIC-

1468, and by Ministerio de Economa y Competitividad

through research grant TIN2012-31518.

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10. D. Catteddu and G. Hogben, Cloud Computing: Benefits,

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Rafael Moreno-Vozmediano is an associate professor in

the Department of Computer Architecture and Sys-

tems Engineer ing at Complutense Universit y of

Madrid (UCM). His research interests include high-

performance and distributed computing, virtualiza-

tion, and cloud computing. Moreno-Vozmediano has a

PhD in computer architecture from UCM. Contact him

at rmoreno@ucm.es.

Rubn S. Montero is the chief architect of the Open Nebula

Project, a cofounder of C12G Labs, and an associate

professor at the Complutense University of Madrid

(UCM). His research interests include resource provi-

sioning models for distributed systems and cloud com-

puting. Montero has a PhD in computer architecture

from UCM. Contact him at rsmontero@opennebula.org.

Ignacio M. Llorente is the director of the OpenNebula Proj-

ect, a cofounder of C12G Labs, and a full professor

at the Complutense University of Madrid (UCM). His

research interests include high-performance comput-

ing, virtualization, cloud computing, and grid tech-

nology. Llorente has a PhD in computer architecture

from UCM and an executive MBA from the Instituto

de Empresa. Hes a member of IEEE. Contact him at

imllorente@opennebula.org.

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