Towards Efficient VM Placement: A Two-Stage ACO-PSO Approach for Green Cloud Infrastructure

Datacenters consume a growing share of energy, prompting the need for sustainable resource management. This paper presents a Hybrid ACO-PSO (HAPSO) algorithm for energy-aware virtual machine (VM) placement and migration in green cloud datacenters. In the first stage, Ant Colony Optimization (ACO) performs energy-efficient initial placement across physical hosts, ensuring global feasibility. In the second stage, a discrete Particle Swarm Optimization (PSO) refines allocations by migrating VMs from overloaded or underutilized hosts. HAPSO introduces several innovations: sequential hybridization of metaheuristics, system-informed particle initialization using ACO output, heuristic-guided discretization for constraint handling, and a multi-objective fitness function that minimizes active servers and resource wastage. Implemented in CloudSimPlus, extensive simulations demonstrate that HAPSO consistently outperforms classical heuristics (BFD, FFD), Unified Ant Colony System (UACS), and ACO-only. Notably, HAPSO achieves up to 25% lower energy consumption and 18% fewer SLA violations compared to UACS at large-scale workloads, while sustaining stable cost and carbon emissions. These results highlight the effectiveness of two-stage bio-inspired hybridization in addressing the dynamic and multi-objective nature of cloud resource management.