Solving Kubernetes error x509: Certificate signed by unknown authority

The Problem

The x509: Certificate signed by unknown authority error in Kubernetes often occurs when the cluster components are not able to authenticate the integrity of the certificates being presented. This error can arise in various scenarios such as when accessing the Kubernetes API server, when nodes communicate with each other, or when pods attempt to communicate with services requiring mutual TLS authentication. To resolve this error, it’s crucial to understand the certificate chain used by Kubernetes and implement solutions that ensure proper certificate recognition and trust.

Solution 1: Verify Certificate Chain

Ensuring that the complete certificate chain is correct and trusted.

1. Inspect the certificates to ensure that they include the full chain from the server certificate to the root certificate authority (CA).
2. Make sure the Kubernetes components are configured to trust the root CA.
3. Check for any expired certificates in the chain and renew them.

Example:

# 1. Inspect Certificate
openssl x509 -in /path/to/server.crt -text -noout

# 2. Update Kubernetes to Trust Root CA - depends on setup

Notes:

• The CA must be trusted by all components that rely on the certificates for communication.
• Overlooking this configuration can lead to persistent trust issues in cluster communication.

Solution 2: Redeploy Kubernetes Component Certificates

Redeploy the certificates used by Kubernetes components if they’re configured incorrectly.

1. Generate new certificates or obtain them from a trusted certificate authority.
2. Replace the current Kubernetes component certificates with the new ones.
3. Restart the affected Kubernetes services to pick up the new certificates.

Example:

# Example steps could vary depending on the setup - consult k8s documentation specific to your setup.

Notes:

• Authenticates communications within the Kubernetes architecture.
• Requires downtime for the component being updated, which could lead to temporary inaccessibility.

Solution 3: Add the CA Certificate to the Host’s Trust Store

Systems might not recognize a certificate because it’s not in the host’s trusted store.

1. Locate the host’s trusted CA store. This will vary based on the operating system.
2. Add the CA certificate that signed the Kubernetes certificate to the trusted store.
3. Restart any processes or components that need to recognize the certificate.

Example:

# For Linux systems, this is typically done using the update-ca-certificates utility
sudo cp /path/to/ca.crt /usr/local/share/ca-certificates/
sudo update-ca-certificates

# Restart Kubernetes components as needed
sudo systemctl restart kubelet

Notes:

• Easy to apply and ensures that all applications on the host trust the certificates issued by the added CA.
• May require additional configuration on systems with more restricted trust stores.

Conclusion

There can be several reasons behind the x509: Certificate signed by unknown authority error in a Kubernetes cluster. This tutorial covered a systematic approach to troubleshooting and rectifying this error through verifying certificate chains, redeploying component certificates, and adding the CA certificate to the host’s trust store. Each solution comes with its benefits and limitations, so it’s essential to choose the one that best fits the circumstances of your Kubernetes setup.