Lab 3.2 node installation failed

Environment: AWS VPC with 2 medium large nodes (ubuntu 16.04 LTS)
Step 6 fails with:

[discovery] Trying to connect to API Server "172.31.57.36:6443"
[discovery] Created cluster-info discovery client, requesting info from "https://172.31.57.36:6443"
[discovery] Requesting info from "https://172.31.57.36:6443" again to validate TLS against the pinned public key
[discovery] Cluster info signature and contents are valid and TLS certificate validates against pinned roots, will use API Server "172.31.57.36:6443"
[discovery] Successfully established connection with API Server "172.31.57.36:6443"
[kubelet] Downloading configuration for the kubelet from the "kubelet-config-1.12" ConfigMap in the kube-system namespace
...
[preflight] Some fatal errors occurred:
    [ERROR FileAvailable--etc-kubernetes-bootstrap-kubelet.conf]: /etc/kubernetes/bootstrap-kubelet.conf already exists
    [ERROR FileAvailable--etc-kubernetes-pki-ca.crt]: /etc/kubernetes/pki/ca.crt already exists
[preflight] If you know what you are doing, you can make a check non-fatal with `--ignore-preflight-errors=...`

Does anyone know what causes this?