Defending the Distributed Skies: A Comprehensive Literature Review of the Arena of Multi-Cloud Environment

The rapid implementation of multi-cloud architectures, such as the integration of services from multiple cloud providers, gives organizations enhanced flexibility, resilience, and vendor independence. However, the multi-cloud model presents complicated security challenges due to diverse platforms, fragmented governance, and increased areas of concern. This paper presents a comprehensive literature review of the multi-cloud environment arena, focusing on the analysis of threats, vulnerabilities, cost optimization, mitigation strategies, and research trends. It covers a comprehensive range of risks, including data breaches, insider threats, API exploitation, configuration errors, and emerging multi-vector attacks, as well as the cumulative complexity of aligning policies, managing identities, and ensuring compliance across diverse providers. The review analyzes existing and proposed defence mechanisms, spanning cryptographic techniques, fuzzy-logic decision frameworks, AI and ML-driven detection systems, as well as integrated Identity and Access Management (IAM) systems. Analysis of relevant literature reveals a progression from basic foundational encryption systems toward more sophisticated, policy-driven, and collaboration-capable security frameworks. Additionally, the paper identifies significant research gaps in real-world validation, cost optimization, and unified governance models. This research departs from prior work by integrating multiple perspectives rather than limiting its scope to a single area such as security, defence, or cost optimization. It also provides new researchers with comprehensive background information on cloud architecture within a single article.