ABSTRACT: Cloud Co mputing gives convenient, on-demand network access to shared pool of co mputing resources like network storage and servers. With On demand use, high scalability and low maintenance cost of Cloud computing more and more enterprises wishes to migrate their legacy application to the cloud environment. Cloud platform itself promises high reliab ility. And also ensures high quality of service. But due to comp licated structure of enterprises application and also large no of distributed components of legacy application the things are becoming complicated. So while migrating any legacy application to the cloud becomes critical and challenging task. To improve reliab ility proposed system gives ROcloud framework i.e. Reliability -Based optimized framework. ROCloud improves the application Reliab ility by using Fault tolerance. ROCloudes includes two ranking algorithms. First Ranking Algorithm is used to rank components for the application when all their co mponents of the application will be migra ted to the cloud. And second ranking algorithm is used to rank components those are hybrid application i.e. when only part of their components are migrated to the cloud. For components both the Ranking algorith ms make use of the Application structure information and historical reliability information. On the basis of ranking results for the most significant components with respect to their predefined co mponents Optimal fault to lerant strategy will be selected automatically. KEYWORDS: Software Reliability, Cloud Migrat ion, Ranking Algorith m, Fault To lerance. I. INTRO DUCTION Cloud computing is a convenient, on-demand network access. It is a shared pool of configurable computing resources. The computing resources like networks, servers, storage, etc., can be prov isioned to cloud users on-demand, in the cloud computing environment. It is like the electricity grid. Without the concern of upfront capital or operator expense n companies can deploy their newly developed Internet services to the cloud. Thus, when migrat ing legacy applications to the cloud environment reliability based optimizat ion is an urgently required research problem In the cloud environment, the applications deployed in the cloud environment are usually complicated. And also consist of a large number of components. So only use of fault prevention techniques and fault removal techniques are not sufficient. Software fault tolerance is another approach for build ing reliab le systems. To tolerate faults wh ich can be emp loy functionally equivalent components. in the cloud environment software fault tolerance approach takes advantage of the redundant resources. And instead of removing faults, it makes the system more robust by masking faults. The cloud platform is flexib le and can provide resources on-demand. Still there is a charge for using the cloud components. e.g., the virtual machines of A mazon Elastic Co mpute Cloud or Simp le Storage Service. Legacy applications usually consist of a large number of co mponents. So providing redundancies for each component is a very expensive task. During the mig ration of legacy applications to cloud, to assure highly reliab ility with reduced cost i.e with limited budget, an efficient reliab ility -based optimizat ion framework is necessary
