Cloud computing is one of the fastest growing technology. Pay-as-you-go model attracts the customer to utilize the large amount of cloud services in very low cost. Scalability and virtualization plays a vital role to achieve this goal. Scalability is the ability to find the number of users and to provide the service accordingly. Scaling can be divided into two, namely Auto-scaling or dynamic scaling and manual scaling. Auto-scaling doing great job to reduce the manual process. Scaling definitely reduces the service and operational cost, badly configured scaling sometimes increases the cost also. In such case there are chances for Service Level Agreement (SLA) violations and poor Quality of service (QoS). The perfect scaling should increase the profit for the Cloud Service Provider (CSP) and reduces the service cost, should not affect the QoS and SLA violations. In this paper, a dynamic rule based auto-scaling mechanism is proposed to reduce the cost of the VM instances.

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Cloud Computing Auto-scaling Virtualization Quality Of Service And Service Level Agreements.