const fluentBit = new k8s.yaml.ConfigFile("fluent-bit.yml", {}, { parent: cluster, provider: cluster.provider });

I had to specify the provider too - I would've thought it could deduce that from the parent?

It definitely should be inferred from the parent. Do you have a full repro you could share in a GitHub issue?

Just tried again now, deleting the resource first, then trying to create without the provider specified:

Type                                                 Name             Plan       Info
     pulumi:pulumi:Stack                                  k8s-infra-dev               
     ├─ eks:index:Cluster                                 Dev-Eks                     
 +   │  └─ kubernetes:yaml:ConfigFile                     fluent-bit.yml   create     
     └─ kubernetes:<http://rbac.authorization.k8s.io:ClusterRole|rbac.authorization.k8s.io:ClusterRole>  fluent-bit-read             1 error
 
Diagnostics:
  kubernetes:<http://rbac.authorization.k8s.io:ClusterRole|rbac.authorization.k8s.io:ClusterRole> (fluent-bit-read):
    error: unable to load Kubernetes client configuration from kubeconfig file: invalid configuration: no configuration has been provided