Kubernetes Authentication: A Simple Guide

Kubernetes is a powerful platform for managing applications. But before we can control it, we must first prove who we are. This is where authentication comes in. In this post, we’ll see how users gain access, how Kubernetes verifies identities, and how we can protect our cluster from threats.

Who Uses Kubernetes?

Kubernetes recognizes different types of users:

• Admins: They manage the cluster, control access, and keep everything running smoothly.
• Developers: They deploy and maintain applications within the cluster.
• Application End Users: These are the people using our apps, but they do not interact with Kubernetes directly.
• Bots (Service Accounts): Automated systems that perform tasks, like CI/CD pipelines or monitoring tools.

Kubernetes does not store users like a typical database. Instead, it depends on external identity providers.

Users vs. Service Accounts

Kubernetes has two main ways to recognize identities:

• Users: These are real people who need access to the cluster. Kubernetes does not manage user accounts. Instead, it relies on external authentication, like certificates, OpenID Connect (OIDC), or LDAP.
• Service Accounts: These are special accounts for applications running inside the cluster. Kubernetes manages these internally and assigns them to pods when needed.

How Kubernetes Authenticates

The Kube API server stands as the cluster's gatekeeper. It verifies every request. When we try to access the cluster, the Kubernetes API server checks our identity. It does this using one of several authentication methods:

• Client Certificates: A secure way to verify users based on a cryptographic key.

curl --cert client.crt --key client.key --cacert ca.crt https://<KUBE_API_SERVER>/api/v1/namespaces/default/pods

• Bearer Tokens: A token-based system, often used for automated tools or external authentication providers.

curl -H "Authorization: Bearer <TOKEN>" https://<KUBE_API_SERVER>/api/v1/namespaces/default/pods

• OpenID Connect (OIDC): A modern approach that integrates with identity providers like Google, Okta, or Keycloak.

curl -H "Authorization: Bearer $(cat oidc-token.txt)" https://<KUBE_API_SERVER>/api/v1/namespaces/default/pods

• Webhook Token Authentication: Calls an external service to validate user credentials.

• Static Password Files (Deprecated): Older method, not recommended for production use.

Once Kubernetes verifies who we are, it checks what actions we are allowed to perform using Role-Based Access Control (RBAC).

Best Practices

Securing our cluster starts with strong authentication practices:

• Use Strong Identity Providers: Integrate with a trusted authentication service, like OIDC or LDAP.
• Avoid Static Credentials: Do not use hardcoded passwords or long-lived tokens.
• Enable RBAC: Grant only the necessary permissions to users and service accounts.
• Rotate Credentials Regularly: Expire and renew tokens or certificates to reduce risk.
• Limit API Access: Restrict API access based on need-to-know.
• Enable Multi-Factor Authentication (MFA): Adds an extra layer of security for admins and developers.
• Monitor and Audit: Track authentication logs to detect suspicious activity.

Conclusion

Authentication is the first step in securing Kubernetes. By understanding how Kubernetes verifies users and by applying best practices, we can keep our cluster safe. Strong authentication ensures that only the right people and systems can control our workloads.