Abstract—Web applications are mostly designed with multiple tiers for flexibility and software reusability. It is difficult to model the behavior of multi-tier Web applications due to the fact that the workload is dynamic and unpredictable and the resource demand in each tier is different. Those features also cause the task of resource allocation for multi-tier Web applications very challenging. In order to meet service level agreements (SLAs) with minimal resource costs, Web service providers should dynamically allocate appropriate resources to each tier. This is particularly important to minimize the monetary cost in the pay-as-you-go cloud computing environments. Recently, a number of rule and model based approaches have been proposed for resource provisioning in cloud computing. In this survey, we identify challenges of the resource allocation problem and conduct a comparative review on those rule and model based approaches for resource allocation in multi-tier Web sites. Given the analysis on their advantages and limitations, we outline research directions to further improve the effectiveness of resource management in multi-tier Web applications. Index Terms—Web service, resource allocation, multi-tier ar-chitecture, learning, control theory. I.