Ensuring Kubernetes Clusters are Accessible Only over HTTPS

In the modern world of containerized applications and microservices, Kubernetes has emerged as the de facto standard for orchestrating and managing containerized workloads. As Kubernetes clusters often handle sensitive data and critical business operations, security is of utmost importance. One crucial security measure is to ensure that Kubernetes clusters are accessible only over HTTPS. This blog post will delve into the core concepts, typical usage examples, common practices, and best practices related to making Kubernetes clusters accessible solely via HTTPS.

Table of Contents

  1. Core Concepts
  2. Typical Usage Example
  3. Common Practices
  4. Best Practices
  5. Conclusion
  6. References

Core Concepts

What is HTTPS?

HTTPS (Hypertext Transfer Protocol Secure) is an extension of the HTTP protocol. It uses the SSL/TLS protocol to encrypt the data transmitted between a client and a server. This encryption ensures that the data cannot be easily intercepted or tampered with by malicious actors. When a Kubernetes cluster is accessible over HTTPS, any communication between the user’s client (e.g., kubectl) and the Kubernetes API server is encrypted.

Why HTTPS for Kubernetes Clusters?

  • Data Confidentiality: Kubernetes clusters store and manage sensitive information such as application configurations, secrets, and authentication tokens. HTTPS ensures that this data remains confidential during transmission.
  • Data Integrity: It prevents attackers from modifying the data in transit. Any attempt to tamper with the encrypted data will result in the decryption process failing on the receiving end.
  • Authentication: HTTPS uses digital certificates to authenticate the identity of the server. This helps users ensure that they are communicating with the legitimate Kubernetes API server and not a malicious imposter.

Kubernetes API Server and HTTPS

The Kubernetes API server is the central management point for the cluster. By default, it listens on HTTPS on port 6443. The API server uses a self - signed certificate during the initial setup, but for production environments, a certificate issued by a trusted Certificate Authority (CA) is recommended.

Typical Usage Example

Prerequisites

  • A running Kubernetes cluster.
  • kubectl configured to communicate with the cluster.
  • A domain name pointed to the Kubernetes API server’s IP address.

Step 1: Obtain an SSL/TLS Certificate

You can obtain an SSL/TLS certificate from a trusted CA such as Let’s Encrypt. There are tools like Cert - Manager that can automate the process of obtaining and renewing Let’s Encrypt certificates in a Kubernetes cluster.

Step 2: Configure the Kubernetes API Server

  1. Create a Secret to store the SSL/TLS certificate and private key:
kubectl create secret tls kube - api - cert --cert=path/to/cert.pem --key=path/to/key.pem
  1. Edit the API server manifest (usually located at /etc/kubernetes/manifests/kube - apiserver.yaml on the control plane nodes). Add the following flags:
- --tls-cert-file=/etc/kubernetes/pki/apiserver.crt
- --tls-private-key-file=/etc/kubernetes/pki/apiserver.key

Replace the paths with the actual paths to the certificate and private key stored in the Secret.

Step 3: Update kubectl Configuration

Update the kubeconfig file to use the new HTTPS endpoint. You can do this by editing the server field in the appropriate context:

apiVersion: v1
clusters:
- cluster:
    certificate-authority-data: <encoded - CA - cert>
    server: https://your - domain.com:6443
  name: your - cluster - name
contexts:
- context:
    cluster: your - cluster - name
    user: your - user - name
  name: your - context - name
current - context: your - context - name
kind: Config
preferences: {}
users:
- name: your - user - name
  user:
    client - certificate - data: <encoded - client - cert>
    client - key - data: <encoded - client - key>

Common Practices

Using Ingress Controllers

Ingress controllers are used to manage external access to services in a Kubernetes cluster. They can be configured to terminate SSL/TLS connections at the edge and forward the traffic to the appropriate services inside the cluster. For example, the Nginx Ingress Controller can be configured to use an SSL/TLS certificate for HTTPS traffic.

Securing Node Ports

If you are using Node Ports to expose services, make sure that the services behind the Node Ports are also accessible over HTTPS. You can use tools like Traefik to handle SSL/TLS termination at the Node Port level.

Monitoring and Logging

Implement monitoring and logging solutions to track HTTPS traffic to the Kubernetes cluster. Tools like Prometheus and Grafana can be used to monitor the health and performance of the API server and other components. Elasticsearch, Logstash, and Kibana (ELK stack) can be used for log collection and analysis.

Best Practices

Use a Trusted CA

As mentioned earlier, use a certificate issued by a trusted CA for the Kubernetes API server. This not only provides better security but also ensures that clients can easily verify the server’s identity without having to add custom CA certificates.

Regularly Rotate Certificates

SSL/TLS certificates have an expiration date. Set up a process to regularly rotate certificates to avoid service disruptions due to expired certificates. Tools like Cert - Manager can automate this process.

Network Segmentation

Implement network segmentation to isolate the Kubernetes API server from other parts of the network. Use firewalls to restrict access to the API server to only authorized IP addresses and ports.

Limit API Server Access

Use Role - Based Access Control (RBAC) to limit who can access the Kubernetes API server. Only grant the necessary permissions to users and service accounts.

Conclusion

Ensuring that Kubernetes clusters are accessible only over HTTPS is a fundamental security measure. It protects the confidentiality, integrity, and authenticity of the data transmitted between clients and the Kubernetes API server. By following the typical usage examples, common practices, and best practices outlined in this blog post, intermediate - to - advanced software engineers can enhance the security of their Kubernetes clusters and protect their critical applications and data.

References