Multi-cloud concept has broaden the world of cloud computing and has become a buzzword today. The word Multi-cloud envisions utilization of services from multiple heterogeneous cloud providers via a single architecture at customer premises. Though cloud computing has many issues and offers open research challenges, still the academics and industrial research has paved a pathway for multi-cloud environment. The concept of multi-cloud is in maturing phase, and many research projects are in progress to provide a multi-cloud architecture which is successfully enabled in all the respects like easy configuration, security, management etc. In this paper, concepts, challenges, requirement and future directions for multi-cloud environment are discussed. A survey of existing approaches and solutions provided by different multi-cloud architectures is entailed along with analysis of the pros and cons of different architectures while comparing the same.