In cloud-centric environments, organizations must reconcile dynamic, geo-distributed workloads with real-time threat monitoring challenges that outstrip traditional, on-premises Intrusion Detection System (IDS) deployments. Network Intrusion Detection System as a Service (NIDSaaS) addresses this gap by delivering packet-inspection capabilities through a unified, on-demand security layer. At its core lies a novel use of VXLAN as a Layer 3 mirroring pathway: client traffic is encapsulated and transported over standard IP networks, decoupling mirror delivery from local switching fabrics. Once in the service domain, mirrored flows are dynamically balanced—via a hash-based distribution scheme—across multiple, elastic analysis instances dedicated to each client. This approach enables horizontal scaling per tenant, continuous redundancy, and fine-grained resource allocation without reliance on proprietary appliances. By abstracting intrusion detection into a subscription-style cloud service, NIDSaaS offloads infrastructure management, adapts seamlessly to traffic fluctuations, and consolidates threat intelligence across dispersed sites. We present the conceptual framework and design principles underpinning NIDSaaS, illustrate how VXLAN-based mirroring and distributed flow balancing unify scalability with resilience, and discuss implications for cost-effective, service-oriented security in next-generation cloud networks.