Mastering Kubernetes Certificates

When running Kubernetes in your own environment, it’s essential to grasp how certificates function and how to oversee them to uphold the security and integrity of your cluster. This article will delve into what a Kubernetes certificate entails, its significance, and the process for verifying and updating the kube-apiserver server certificate.

Kubernetes certificates play a pivotal role in securing communications among various components of the Kubernetes platform. They facilitate the establishment of secure connections, encryption of data in transit, and authentication of Kubernetes components’ identities. Inadequate certificate management can leave your cluster susceptible to unauthorized access, data breaches, and other security vulnerabilities.

Imagine you have a Kubernetes cluster hosting multiple applications, each housing sensitive customer data. If the kube-apiserver server certificate, responsible for authenticating the API server, expires without being renewed, it can disrupt communication between components, exposing your cluster to potential threats. It’s imperative to proactively manage certificates to mitigate such security risks.

What are Kubernetes certificates?

Kubernetes certificates serve as digital documents essential for authentication, authorization, and encryption within a Kubernetes cluster. They play a crucial role in verifying the identities of different entities within the cluster, including nodes, users, and services. Based on the widely adopted X.509 standard, these certificates adhere to a prevalent public key infrastructure (PKI) certificate format.

Each Kubernetes certificate comprises two primary components: a private key and a public key. The private key remains confidential and is utilized for signing and decrypting data. On the other hand, the public key is shared widely and serves to validate signatures and encrypt data securely.

Types of Kubernetes certificates

There are several types of certificates used in Kubernetes clusters, each with a specific purpose:

1. Node certificates : These certificates, also known as kubelet certificates, are used by Kubernetes nodes to authenticate themselves to the control plane. Node certificates are generated and managed by the cluster’s Certificate Authority (CA) and are used for secure communication between nodes and control plane components.
2. User certificates : User certificates are used to authenticate users of the Kubernetes cluster, such as administrators and developers. These certificates are typically issued by the cluster’s CA and are used to authenticate users when interacting with the cluster through the Kubernetes API server or other Kubernetes components.
3. Service account certificates : Service account certificates are used to authenticate Kubernetes services and applications running within the cluster. They are automatically created by Kubernetes for each service account and are used to verify service-to-service communication within the cluster.
4. API server certificate : API server certificates are used to secure communications between the Kubernetes API server and other Kubernetes components such as kubelet, etcd, and controllers. These certificates are signed by the cluster’s CA and are critical to ensuring the security of the Kubernetes cluster control plane.
5. Etcd certificate : Etcd is a distributed key-value store used by Kubernetes to store cluster configuration data. Etcd certificates are used to secure communications between etcd nodes and other components in the cluster. These certificates are generated and managed by the cluster’s CA and play a vital role in ensuring the security of Kubernetes cluster configuration data.

Why are Kubernetes certificates important?

Kubernetes certificates serve critical purposes within a cluster environment. Firstly, they play a vital role in safeguarding the integrity of data transmitted throughout the Kubernetes cluster. By encrypting data during transit between components, these certificates mitigate the risk of unauthorized access to sensitive information.

Secondly, Kubernetes certificates facilitate the verification of Kubernetes components’ identities. This verification process helps thwart potential security breaches by preventing malicious entities from masquerading as legitimate components, thus safeguarding sensitive data from unauthorized access.

Lastly, Kubernetes certificates contribute to the overall security posture of the Kubernetes cluster. Through the establishment of secure connections between different components, these certificates help thwart threats that could compromise the entire cluster’s security, ensuring the continued integrity and operation of the environment.

Check certificate validity period

You can easily check the expiration date of the kube-apiserver server certificate using OpenSSL or CFSSL. By running a simple command, you can extract the certificate and view its expiration date. For example, using OpenSSL, you can run the following command.

openssl x509 -noout -enddate -in /etc/kubernetes/pki/apiserver.crt
notAfter=Mar  8 12:50:57 2024 GMT

This will display the expiration date of the certificate. Likewise, using CFSSL you can run the following command to view the expiration date. Keeping track of this date and renewing certificates before they expire is important to maintaining cluster security.

cfssl-certinfo -cert /etc/kubernetes/pki/apiserver.crt

Get expiration date from kubeadm:

kubeadm certs check-expiration
[check-expiration] Reading configuration from the cluster...
[check-expiration] FYI: You can look at this config file with 'kubectl -n kube-system get cm kubeadm-config -o yaml'

CERTIFICATE                EXPIRES                  RESIDUAL TIME   CERTIFICATE AUTHORITY   EXTERNALLY MANAGED
admin.conf                 Mar 08, 2024 12:52 UTC   323d            ca                      no
apiserver                  Mar 08, 2024 12:50 UTC   323d            ca                      no
apiserver-etcd-client      Mar 08, 2024 12:50 UTC   323d            etcd-ca                 no
apiserver-kubelet-client   Mar 08, 2024 12:50 UTC   323d            ca                      no
controller-manager.conf    Mar 08, 2024 12:51 UTC   323d            ca                      no
etcd-healthcheck-client    Feb 19, 2024 22:33 UTC   305d            etcd-ca                 no
etcd-peer                  Feb 19, 2024 22:33 UTC   305d            etcd-ca                 no
etcd-server                Feb 19, 2024 22:33 UTC   305d            etcd-ca                 no
front-proxy-client         Mar 08, 2024 12:50 UTC   323d            front-proxy-ca          no
scheduler.conf             Mar 08, 2024 12:52 UTC   323d            ca                      no

CERTIFICATE AUTHORITY   EXPIRES                  RESIDUAL TIME   EXTERNALLY MANAGED
ca                      Feb 08, 2033 16:30 UTC   9y              no
etcd-ca                 Feb 08, 2033 16:30 UTC   9y              no
front-proxy-ca          Feb 08, 2033 16:30 UTC   9y              no

Update certificate

Updating the kube-apiserver server certificate is a simple process using the kubeadm command. You can run “kubeadm certs renew apiserver” to renew the certificate and update the certificate with the new expiration date.

kubeadm certs renew apiserver
[renew] Reading configuration from the cluster...
[renew] FYI: You can look at this config file with 'kubectl -n kube-system get cm kubeadm-config -o yaml'

certificate for serving the Kubernetes API renewed

Renewing your certificate before it expires ensures the continued security and smooth operation of your Kubernetes cluster.

Operational points

1. Periodically check the expiration date of the kube-apiserver server certificate using OpenSSL or CFSSL.
2. Use the kubeadm command to renew the certificate before it expires.
3. Track the expiration dates of all certificates in your Kubernetes cluster and ensure they are updated in a timely manner.
4. Stay up to date on Kubernetes security best practices and adhere to them to protect your cluster.
5. Regularly review and update security measures for Kubernetes clusters to protect against potential security threats.

Hopefully this article has provided you with valuable insights into Kubernetes certificates and their importance in securing your cluster. Remember, a proactive approach to certificate management is critical to maintaining the security and integrity of your Kubernetes environment. Stay vigilant and keep your cluster safe!

Conclusion

In summary, Kubernetes certificates are an important part of ensuring the security of a Kubernetes cluster. By understanding what they are, why they are important, and how to manage them, you can keep your cluster secure and protect your applications and data from potential security risks. Regularly checking and updating the kube-apiserver server certificate is necessary to ensure the continued security of the cluster. Therefore, don’t neglect certificate management to ensure your Kubernetes cluster is secure !