The Trouble with Tar: Introducing High Availability, Zone-Aware Load Balancing

In a blog post by William Morgan, the challenges of Topology Aware Routing (TAR) in Kubernetes are discussed. TAR restricts traffic within availability zones to save costs but can reduce system reliability by preventing pods in one zone from compensating for failures in others. While TAR is resilient to certain failures detected by liveness and readiness probes, it cannot handle in-band failures like application errors or broken dependencies. To address these limitations, service meshes like Linkerd offer in-band health checking, fine-grained traffic control, and the ability to handle cross-cluster traffic. Buoyant Enterprise for Linkerd introduces High Availability Zonal Load Balancing (HAZL) as a solution. HAZL dynamically balances traffic within and across zones to maintain high availability while reducing costs in multi-zone Kubernetes clusters. By leveraging features like in-band health checking and fine-grained traffic control, HAZL aims to provide a more flexible and reliable alternative to TAR for Kubernetes adopters seeking optimal cloud cost management and system reliability.