Implementing Global Server Load Balancing with k8gb: A DNS‑Based GSLB Solution for Multi‑Cluster Kubernetes

Balancing traffic among multiple Kubernetes clusters and achieving automatic disaster‑recovery failover has long been a difficult problem. Existing approaches such as commercial GSLB products, public‑cloud global load balancers, Karmada Multi‑Cluster Ingress, and manual DNS setups each suffer from high cost, limited flexibility, poor cloud‑native integration, or scalability issues.

What is GSLB? Global Service Load Balancer (GSLB) operates above the cluster level, distributing traffic across several clusters and providing geographic routing and automatic failover when a cluster becomes unhealthy.

Problems with other solutions:

Commercial GSLB: expensive, vendor‑locked, and requires separate hardware outside the Kubernetes environment.

Public‑cloud global load balancers (e.g., AWS Global Accelerator, GCP External Application Load Balancer): limited to a single cloud provider and cannot be used in private‑cloud scenarios.

Karmada Multi‑Cluster Ingress: depends on complex CRDs, requires additional ingress‑nginx instances, and the project shows little recent activity.

Simple DNS‑based methods: manual management does not scale, health checks cannot detect partial failures, DNS caching introduces latency, and many providers lack the needed health‑check features.

k8gb's solution: k8gb also uses DNS but forwards external DNS queries to a CoreDNS instance running inside each cluster. This CoreDNS performs the sophisticated DNS logic, selecting an appropriate Ingress IP based on Ingress specifications, health of backend Pods, and load‑balancing policies. The external DNS only acts as a proxy, eliminating the need for complex health checks or frequent IP updates.

The request flow is:

User queries an external DNS for a domain's IP.

The external DNS proxies the request to the CoreDNS managed by k8gb inside the cluster.

k8gb evaluates Ingress rules, IPs, and pod health to return a viable Ingress IP.

The user connects directly to the chosen Ingress controller.

If a cluster's CoreDNS fails, other clusters can still respond with their Ingress IPs, providing automatic failover.

k8gb also synchronizes CoreDNS records across clusters. Each cluster registers its Ingress IPs under a special sub‑domain (e.g., localtargets-app.cloud.example.com ) so that every cluster can resolve the same domain to healthy IPs from any cluster, effectively achieving multi‑cluster DNS data synchronization.

In summary, k8gb offers an open‑source, cloud‑native GSLB implementation that tightly integrates with Kubernetes, automates cross‑cluster domain and traffic management, and reduces external dependencies to a single DNS record, making it a compelling solution for multi‑cloud environments.