Relevance of the CAP-Theorem for Highly Available, Distributed Storage Systems and the Impact on Cloud-based Applications

This article was published as an university assignment in November 2012

Abstract

The CAP-Theorem states that when building distributed systems only two of the three desired properties can be reached at a time: availability, consistency and partition tolerance. Network failures are considered to be a given in every distributed system, therefore consistency properties are relaxed in order to meet the high availability requirements. The weak consistency properties of a distributed storage system are propagated to the application level. Developers of cloud-based applications have to be aware of the potentially inconsistent state of the data in the underlying storage system and have to treat the data accordingly. An important issue in this context is the effect the inconsistent state of the data has on the end user. There are different approaches for adapting the application design in order to hide these inconsistencies from the end user.

1 Introduction

Cloud computing offers an efficient, flexible and low cost solution for the incessantly increasing business demands: IT-resources as a service. The internet provides the opportunity to reach a huge audience of potential users and customers. At the same time, the availability of these various new possibilities entails a new kind of requirements that have to be met by…