Self-trained Proactive Elasticity Manager for Cloud-based Storage Services

Abstract: The pay-as-you-go pricing model and the illusion of unlimited resources makes cloud computing a conducive environment for provision of elastic services where different resources are dynamically requested and released in response to changes in their demand. The benefit of elastic resource allocation to cloud systems is to minimize resource provisioning costs while meeting service level objectives (SLOs). With the emergence of elastic services, and more particularly elastic key-value stores, that can scale horizontally by adding/removing servers, organizations perceive potential in being able to reduce cost and complexity of large scale Web 2.0 applications. A well-designed elasticity controller helps reducing the cost of hosting services using dynamic resource provisioning and, in the meantime, does not compromise service quality. An elasticity controller often needs to be trained either online or offline in order to make it intelligent enough to make decisions on spawning or removing extra instances when workload increase or decrease. However, there are two main issues on the process of control model training. A significant amount of recent works train the models offline and apply them to an online system. This approach may lead the elasticity controller to make inaccurate decisions since not all parameters can be considered when building the model offline. The complete training of the model consumes large efforts, including modifying system setups and changing system configurations. Worse, some models can even include several dimensions of system parameters. To overcome these limitations, we present the design and evaluation of a self-trained proactive elasticity manager for cloud-based elastic key-value stores. Our elasticity controller uses online profiling and support vector machines (SVM) to provide a black-box performance model of an application’s SLO violation for a given resource demand. The model is dynamically updated to adapt to operating environment changes such as workload pattern variations, data rebalance, changes in data size, etc. We have implemented and evaluated our controller using the Apache Cassandra key-value store in an OpenStack Cloud environment. Our experiments with artificial workload traces shows that our controller guarantees a high level of SLO commitments while keeping the overall resource utilization optimal.