A Survey on Hybrid and Multi-Cloud Environments: Integration Strategies, Challenges, and Future Directions

The rapid evolution of cloud computing has led organizations to adopt hybrid and multi-cloud environments to meet increasing demands for scalability, flexibility, and resilience. While these environments provide significant benefits, they introduce unique challenges, including interoperability, data consistency, security, and vendor lock-in. This survey comprehensively reviews deployment architectures, integration strategies, middleware roles, and the challenges associated with multi-vendor cloud systems. The survey results reveal that middleware plays a critical role in enabling seamless communication, abstraction, orchestration, and maintainability across heterogeneous cloud platforms. Widely adopted integration strategies identified include API-driven integration, service-oriented architectures (SOA), containerization with orchestration, cloud brokers, and Middleware-as-a-Service (MWaaS). These strategies effectively mitigate heterogeneity, support workload portability, and enhance security, thereby enabling scalable and resilient multi-cloud deployments. Additionally, the survey highlights the operational complexities and open research challenges, emphasizing the need for standardized interfaces, unified governance frameworks, and automated management solutions. The findings provide a roadmap for enterprises to implement robust multi-cloud integration frameworks while addressing operational, security, and compliance requirements. This study contributes to a deeper understanding of hybrid and multi-cloud ecosystems, guiding future research toward adaptive middleware, AI-driven orchestration, and edge-cloud integration for enhanced performance, flexibility, and secure adoption.