kubernetes-the-hard-way/docs/04-certificate-authority.md

Provisioning a CA and Generating TLS Certificates

In this lab you will provision a PKI Infrastructure using openssl to bootstrap a Certificate Authority, and generate TLS certificates for the following components: kube-apiserver, kube-controller-manager, kube-scheduler, kubelet, and kube-proxy. The commands in this section should be run from the jumpbox.

Certificate Authority

In this section you will provision a Certificate Authority that can be used to generate additional TLS certificates for the other Kubernetes components. Setting up CA and generating certificates using openssl can be time-consuming, especially when doing it for the first time. To streamline this lab, I've included an openssl configuration file ca.conf, which defines all the details needed to generate certificates for each Kubernetes component.

Take a moment to review the ca.conf configuration file:

cat ca.conf

You don't need to understand everything in the ca.conf file to complete this tutorial, but you should consider it a starting point for learning openssl and the configuration that goes into managing certificates at a high level.

Every certificate authority starts with a private key and root certificate. In this section we are going to create a self-signed certificate authority, and while that's all we need for this tutorial, this shouldn't be considered something you would do in a real-world production level environment.

Generate the CA configuration file, certificate, and private key:

{
  openssl genrsa -out ca.key 4096
  openssl req -x509 -new -sha512 -noenc \
    -key ca.key -days 3653 \
    -config ca.conf \
    -out ca.crt
}

Results:

ca.crt ca.key

Create Client and Server Certificates

In this section you will generate client and server certificates for each Kubernetes component and a client certificate for the Kubernetes admin user.

Generate the certificates and private keys:

certs=(
  "admin" "node-0" "node-1"
  "kube-proxy" "kube-scheduler"
  "kube-controller-manager"
  "kube-api-server"
  "service-accounts"
)

for i in ${certs[*]}; do
  openssl genrsa -out "${i}.key" 4096

  openssl req -new -key "${i}.key" -sha256 \
    -config "ca.conf" -section ${i} \
    -out "${i}.csr"
  
  openssl x509 -req -days 3653 -in "${i}.csr" \
    -copy_extensions copyall \
    -sha256 -CA "ca.crt" \
    -CAkey "ca.key" \
    -CAcreateserial \
    -out "${i}.crt"
done

The results of running the above command will generate a private key, certificate request, and signed SSL certificate for each of the Kubernetes components. You can list the generated files with the following command:

ls -1 *.crt *.key *.csr

Distribute the Client and Server Certificates

In this section you will copy the various certificates to each machine under a directory that each Kubernetes components will search for the certificate pair. In a real-world environment these certificates should be treated like a set of sensitive secrets as they are often used as credentials by the Kubernetes components to authenticate to each other.

Copy the appropriate certificates and private keys to the node-0 and node-1 machines:

for host in node-0 node-1; do
  ssh root@$host mkdir /var/lib/kubelet/
  
  scp ca.crt root@$host:/var/lib/kubelet/
    
  scp $host.crt \
    root@$host:/var/lib/kubelet/kubelet.crt
    
  scp $host.key \
    root@$host:/var/lib/kubelet/kubelet.key
done

Copy the appropriate certificates and private keys to the server machine:

scp \
  ca.key ca.crt \
  kube-api-server.key kube-api-server.crt \
  service-accounts.key service-accounts.crt \
  root@server:~/

The kube-proxy, kube-controller-manager, kube-scheduler, and kubelet client certificates will be used to generate client authentication configuration files in the next lab.

Next: Generating Kubernetes Configuration Files for Authentication