How capable is Pulumi for kubernetes configuration, or is there another GitOps tool for this? (KubeSpray, WeaveWorks, ..)

Depending on what you mean by configuration (bootstrap or when running workloads). Personally we use Pulumi (used to be terraform) for bootstrapping and maintaining the “azure parts” of the cluster, and Flux to maintain in cluster config (cert manager, linkerd, ingresses, applications etc). Imo they are a great match 🙂

Thank you. Why use Flux over Argo?

Simplicity