Yggdrasil is an Envoy control plane that configures listeners and clusters based on Kubernetes ingresses from multiple Kube Clusters. This allows you to have an envoy cluster acting as a mutli-cluster loadbalancer for Kubernetes. We built this because we needed our apps to be highly available in the event of a cluster outage but did not want the solution to live inside of Kubernetes itself.
Yggdrasil will watch all Ingresses in each Kubernetes Cluster that you give it via the Kubeconfig flag. Any ingresses that match any of the ingress classes that you have specified will have a listener and cluster created that listens on the same Host as the Host defined in the Ingress object. If you have multiple clusters Yggdrasil will create a cluster address for each Kubernetes cluster your Ingress is in, the address is the address of the ingress load balancer.