Calculating the CA Certificate Hash for Kubeadm
When using kubeadm to set up a new Kubernetes cluster, the output of the kubeadm init command that sets up the control plane for the first time contains some important information on joining additional nodes to the cluster. One piece of information in there that (until now) I hadn’t figured out how to replicate was the CA certificate hash. (Primarily I hadn’t figured it out because I hadn’t tried.) In this post, I’ll share how to calculate the CA certificate hash for kubeadm to use when joining additional nodes to an existing cluster.
When looking to figure this out, I first started with the kubeadm documentation. My searches led me here, which states:
The hash is calculated over the bytes of the Subject Public Key Info (SPKI) object (as in RFC7469). This value is available in the output of “kubeadm init” or can be calculated using standard tools.
That’s useful information, but what are the “standard tools” being referenced? I knew that a lot of work had been put into kubeadm init phase (for breaking down the kubeadm init workflow), but a quick review of that documentation didn’t reveal anything. Reviewing the referenced RFC also didn’t provide any Continue reading








