Flexible Multi-step Resource Relocation for Virtual Network Functions

Virtual machine (VM) migration is a technology dealing with the process of relocating a VM from one host to another. The relocation of VMs is usually assumed to be done in a single-step procedure, which however leads to a restriction on the degree of freedom. We therefore aim to consider a situation in which multi-step VM migrations are allowed. In this paper, by applying the concept of time-expanded networks [1], a novel optimisation model for virtual network function migration in multiple steps is introduced. Our model is based on the problem of virtual network embedding (VNE), which pertains to the mapping of virtual networks onto a capacitated substrate network and tackles the transition from one mapping to another in multiple passes. This publication is an extension of our previous work [2], which introduced the concept of soft bottlenecks and assumed deadline-restricted VM migrations. The work presented in this paper removes this restriction by allowing the migration time to vary in compliance with a variable VM image transfer rate, making the transition even more flexible. The obtained performance evaluation results underline the advantages of our multi-step VM migration model compared to any conventional single-step VM migration approaches.