Availability modeling in redundant OpenStack private clouds

Abstract

In cloud computing services, high availability is one of the quality of service requirements which is necessary to maintain customer confidence. High availability systems can be built by applying redundant nodes and multiple clusters in order to cope with software and hardware failures. Due to cloud computing complexity, dependability analysis of the cloud may require combining state-based and nonstate-based modeling techniques. This article proposes a hierarchical model combining reliability block diagrams and continuous time Markov chains to evaluate the availability of OpenStack private clouds, by considering different scenarios. The steady-state availability, downtime, and cost are used as measures to compare different scenarios studied in the article. The heterogeneous workloads are considered in the proposed models by varying the number of CPUs requested by each customer. Both hardware and software failure rates of OpenStack components used in the model are collected via setting up a real OpenStack environment applying redundancy techniques. Results obtained from the proposed models emphasize the positive impact of redundancy on availability and downtime. Considering the tradeoff between availability and cost, system providers can choose an appropriate scenario for a specific purpose. K E Y W O R D S availability modeling, cloud computing, continuous time Markov chains, hierarchical models, reliability block diagrams INTRODUCTIONCloud computing includes different resources of one or more data centers, such as storage, network and compute, shared through virtualization technology. 1 Infrastructure as a service (IaaS) is an important service model of the cloud computing paradigm in which providers allocate virtual computing resources as virtual machines (VMs) on physical machines (PMs) to customers over the internet. [2][3][4] According to Gartner, 5 the market for public cloud will reach over $306.9 billion at the end of 2021 and $364 billion at the end of 2022. Gartner expects the hyperscale providers, such as Amazon AWS, Google Cloud Platform, Alibaba, and Microsoft Azure, to account for 70% of the market by the end of 2021. 6 Large organization and government agencies usually like to develop their own cloud data centers for satisfying their needs. By contrast, small organizations usually rent cloud resources from cloud providers to solve their own problems. 7

Predicting locally manageable resource failures of high availability clusters

“…Business‐critical enterprise applications (EAs) hosted on cloud and on‐premises in domains ranging from healthcare and finance to logistics and manufacturing require continuous availability to ensure that service delivery is undisrupted. If the availability of such applications is disrupted for even a short time, the consequences can be severe, such as significant financial loss 1‐5 . The term high availability (HA) refers to how availability can be improved by providing continuous availability.…”