Blockchain interoperability is increasingly recognized as the centerpiece for robust interactions among decentralized services. Blockchain ledgers are generally tamper-proof and thus enforce non-repudiation for transactions recorded within the same network. However, such a guarantee does not hold for cross blockchain transactions. When disruptions occur due to malicious activities or system failures within one blockchain network, foreign networks can take advantage by denying legitimate claims or mounting fraudulent liabilities against the defenseless network. In response, this paper introduces InterSnap, a novel blockchain snapshot archival methodology, for enabling auditability of cross blockchain transactions, enforcing non-repudiation. InterSnap introduces cross-chain transaction receipts that ensure their irrefutability. Snapshots of ledger data along with these receipts are utilized as non-repudiable proof of bilateral agreements among different networks. InterSnap enhances system resilience through a distributed snapshot generation process, need-based snapshot scheduling process, and archival storage and sharing via decentralized platforms. Through a prototype implementation based on Hyperledger Fabric, we conducted experiments using on-premise machines, AWS public cloud instances, as well as a private cloud infrastructure. We establish that InterSnap can recover from malicious attacks while preserving cross chain transaction receipts. Additionally, our proposed solution demonstrates adaptability to increasing loads while securely transferring snapshot archives with minimal overhead.

Multi-cloud environments such as OnApp and Cloudflare have turned the cloud marketplace towards a new horizon where end-users can host applications transparently over different cloud service providers (CSPs) simultaneously by taking the best from each. Existing cloud federations are typically driven by a broker service which provides a trusted interface allowing the participant CSPs and end-users to coordinate. However, such a broker has the limitations of any centralized trusted authority like risk of manipulation, bias, censorship, single point of failure, etc. In this paper, we propose a decentralized trustless cloud federation architecture calledCollabCloudwhich eliminates any central mediator while addressing the challenges introduced by byzantine participants.CollabCloudutilizes blockchain, and introduces a novel interoperability protocol bridging a permissionless blockchain as an open interface for the end-users, and a permissioned blockchain as a coordination platform for the CSPs. We have implementedCollabCloudwith Ethereum, Hyperledger Fabric and Burrow platforms. Experiments with a proof-of-concept testbed emulating 3 CSPs show thatCollabCloudcan operate within an acceptable response latency for resource allocation, while scaling upto 64 parallel requests per second. Scalability analysis over Mininet emulation platform indicates that the platform can scale well with minimal impact on the response latency as the number of participating CSPs increases. % for resource scheduling and allocation. %trustless, transparency, immutability properties of %By utilizing trustless, transparency, immutability and verifiability features of a distributed ledger technology, % Such multi-cloud environments bring the notion of cloud federation where various CSPs can buy and sell cloud resources, and thus collaborate among themselves to provide better capacity with less capital expenditure. %The novelty ofCollabCloudis in designing the interfacing between the two different blockchain platforms, through which the end-users access resources over multi-clouds in a secured way. %Need to reduce to 200 words. %The broker works like a trusted entity that takes care of various management tasks of the federation. %as the decentralized federation marketplace needs to provide a unified interface to the end-users while maintaining an agreement on pricing, fair scheduling of resources and securing resource access to the end-users. %InCollabCloud, we achieve the above goals by developing a unique interface through interconnecting a public (permissionless) blockchain platform with a private (permissioned) blockchain platform. %Cloud federation helps multiple cloud service providers to come into collaboration and share their resources for their overall benefit. However, the current implementations of federated clouds depend on a trusted federation broker that takes care of the handling end-user requests, resource allocation as well as scheduling and pricing for the shared resources under the federation. This central broker provides a unified interface to the end-users, through which they can access the federation as a single entity. The unified interface presents the federation as a single larger cloud provider which can fulfill a broader set of user demands and at a better pricing. Although the cloud broker plays a crucial role in the federation, it has the limitations of any centralized trusted authority like risk of manipulation, biasness, censorship, single point of failure, etc.. In this work, we propose a trustless, decentralized and democratic architecture for cloud federations which is free from any cloud broker. This democratic system leverages a combination of permissionless and permissioned blockchain which keeps all the functionalities of a broker based federation intact. Our system provides a trustless unified interface for the federation as well as brokerless scheduling, transfer of resources, catalog maintainance etc.. We implement the system with a fair scheduling smart contract and evaluate it with respect to end-to-end request processing time and analyze its overheads. The outcome of the analysis gives a clear view that the proposed system keeps all functionalities of cloud federation intact, while maintaining the required quality of experience(QoE) to the end-users.

Applications hosted in commercial clouds are typically multi-tier and comprise multiple tightly coupled virtual machines (VMs). Service providers (SPs) cater to the users using VM instances with different configurations and pricing depending on the location of the data center (DC) hosting the VMs. However, selecting VMs to host multi-tier applications is challenging due to the trade-off between cost and quality of service (QoS) depending on the placement of VMs. This paper proposes a multi-cloud broker model calledCoMCLOUDto select a sub-optimal VM coalition for multi-tier applications from an SP with minimum coalition pricing and maximum QoS. To strike a trade-off between the cost and QoS, we use an ant-colony-based optimization technique. The overall service selection game is modeled as a first-price sealed-bid auction aimed at maximizing the overall revenue of SPs. Further, as the hosted VMs often face demand spikes, we present a parallel migration strategy to migrate VMs with minimum disruption time. Detailed experiments show that our approach can improve the federation profit up to 23% at the expense of increased latency of approximately 15%, compared to the baselines.

Virtual machine (VM) migration enables cloud service providers (CSPs) to balance workload, perform zero-downtime maintenance, and reduce applications’ power consumption and response time. Migrating a VM consumes energy at the source, destination, and backbone networks, i.e., intermediate routers and switches, especially in a Geo-distributed setting. In this context, we propose a VM migration model called Low Energy Application Workload Migration (LEAWM) aimed at reducing the per-bit migration cost in migrating VMs over Geo-distributed clouds. With a Geo-distributed cloud connected through multiple Internet Service Providers (ISPs), we develop an approach to find out the migration path across ISPs leading to the most feasible destination. For this, we use the variation in the electricity price at the ISPs to decide the migration paths. However, reduced power consumption at the expense of higher migration time is intolerable for real-time applications. As finding an optimal relocation is$\mathcal {NP}$-Hard, we propose anAnt Colony Optimization(ACO) based bi-objective optimization technique to strike a balance between migration delay and migration power. A thorough simulation analysis of the proposed approach shows that the proposed model can reduce the migration time by 25%–30% and electricity cost by approximately 25% compared to the baseline.

Interoperation between permissioned consortium blockchain networks relies on their abilities to discover and validate the identities of each others’ participant organizations. These organizations may possess self-sovereign decentralized identities and verifiable credentials issued by well-known certification authorities. Two mutually untrusting networks of organizations can establish a basis for interoperation if they have one or more certification authorities in common. Yet, for privacy reasons, neither of them may want to expose a priori their entire lists of authorities, necessitating a negotiation process through which common authorities can be identified. In this paper, we analyze this negotiation problem, and propose and analyze two solution approaches, one involving active participation of the trust anchors and the other without involving them.

With the increasing adoption of private blockchain platforms, consortia operating in various sectors such as trade, finance, logistics, etc., are becoming common. Despite having the benefits of a completely decentralized architecture which supports transparency and distributed control, existing private blockchains limit the data, assets, and processes within its closed boundary, which restricts secure and verifiable service provisioning to the end-consumers. Thus, platforms such as e-commerce with multiple sellers or cloud federation with a collection of cloud service providers cannot be decentralized with the existing blockchain platforms. This paper proposes a decentralized gateway architecture interfacing private blockchain with end-users by leveraging the unique combination of public and private blockchain platforms through interoperation. Through the use case of decentralized cloud federations, we have demonstrated the viability of the solution. Our testbed implementation with Ethereum and Hyperledger Fabric, with three service providers, shows that such consortium can operate within an acceptable response latency while scaling up to 64 parallel requests per second for cloud infrastructure provisioning. Further analysis over the Mininet emulation platform indicates that the platform can scale well with minimal impact over the latency as the number of participating service providers increases.

Facebook’s “Mark Yourself Safe” or Google Person Finder are quite popular nowadays. Such applications generate crisis maps based on crowdsourced information during or after disasters. Crisis maps are inevitably an extremely effective digital dashboard application for rescue and reliefs. But what if there is even a partial Internet blackout after the disaster strikes? This is indeed a common scenario, but today’s crisis mapping solutions heavily depend on the Internet. In this paper, we discuss a thorough background study and design details of Soteria, an end-to-end solution for smartphone-based opportunistic crisis mapping in the fate of Internet blackouts. Soteria uses intelligent and energy-efficient mechanisms for opportunistic ad-hoc information collection and filtering along with data summarization and dashboard application for crisis mapping over end-users’ smartphones. The smartphone application intelligently incorporates and tunes the existing network systems and services at the backend to make the system work even when the conventional network infrastructure fails. We evaluate the performance of Soteria from multiple field-trials for over five years, and the observed quantitative and qualitative performance is extremely promising for its mass-scale adoption at the disaster-prone areas.

This paper proposes a virtual machine (VM) migration model to reduce the power consumption while migrating a set of VMs over geo-distributed clouds. We develop an approach to find out the migration path across different Internet Service Providers (ISPs) leading to the most feasible destination. For this, we make use of the variation in the electricity price at the ISPs for deciding the migration paths. However, reduced power consumption at the expense of higher migration time is intolerable for real-time applications. Hence, we propose an Ant Colony Optimization (ACO) based bi-objective optimization technique to strike a balance between the power consumption and the migration time to make the implementation realistic. Thorough simulation analysis of the proposed approach shows that it can achieve low power consumption cost with acceptable migration time.