Cloud computing is a new paradigm in the field of distributed computing. The objective of cloud computing is to provide various computing resources over the internet in the form of service to number of cloud consumers. Cloud provides the computing environment to organization in a cost effective manner and give flexibility to increase the number of resources as required during peak load time. In this paper we have tried to highlight some of the major challenges like security, availability of cloud services, reliability and auto-provisioning of cloud resources etc. which need to be addressed by researchers. Certainly there are some performance implications which also need to be resolved in order to get maximum output from the cloud so we need to manage the cloud resources in optimized way to increase the performance of cloud and its adaptability among different organization.