Currently, there is an issue with "yum install" used by the node-agent, as described in the known issues from Google Cloud here.

As a result, the automatic installation of the repositories kubelet and google-cloud-sdk is not possible without manual intervention.

It is still possible to install the repositories manually so that the node-agent can install all the other dependencies, but this requires to connect to all nodes, stop the node-agent, switch off repo-gpgcheck, install kubelet manually and start the node-agent again:

sudo systemctl stop node-agentd
sudo sed -i 's/repo_gpgcheck=1/repo_gpgcheck=0/g' /etc/yum.repos.d/google-cloud.repo
sudo yum install -y google-cloud-sdk
sudo systemctl stop node-agentd
sudo sed -i 's/repo_gpgcheck=1/repo_gpgcheck=0/g' /etc/yum.repos.d/kubernetes.repo
sudo yum install -y kubelet-1.18.8-0
sudo systemctl start node-agentd

As this is an issue on side of the repositories, we don't plan on including a fix on our side as a workaround.