Understanding SSL/TLS in Kubernetes

Welcome back to the CK2024 series! In this 21st instalment, we delve into the crucial topic of SSL/TLS within Kubernetes. Building on our previous discussion about SSL/TLS basics, this blog will explore how these security protocols are implemented in Kubernetes environments, focusing on certificate creation, signing requests, and overall security mechanisms.

Recap of SSL/TLS Basics

Before diving into Kubernetes specifics, let's briefly revisit the fundamental concepts of SSL/TLS. SSL (Secure Sockets Layer) and its successor TLS (Transport Layer Security) are cryptographic protocols designed to secure communications over a network. They use a combination of symmetric and asymmetric encryption to ensure the confidentiality and integrity of data.

In a typical SSL/TLS setup:

• Client Certificates: Issued by clients to authenticate themselves to the server.
• Server Certificates: Issued to servers to encrypt communication and authenticate themselves to clients.
• Certificate Authority (CA): The entity that issues and signs certificates. It validates the identity of the certificate requester before issuing a certificate.

SSL/TLS in Kubernetes

Kubernetes, as a container orchestration platform, also relies on SSL/TLS for securing communications between its various components. Here’s a breakdown of how SSL/TLS operates within a Kubernetes cluster:

1. Components Involved:

• Master Node: Manages the Kubernetes cluster and contains components like the API server, controller manager, and scheduler.
• Worker Nodes: Host the containerized applications.
• Clients: Users or tools like kubectl that interact with the Kubernetes API server.

1. Certificate Types:

• Client Certificates: Used by users or clients to authenticate with the Kubernetes API server.
• Server Certificates: Used by the API server and other components to secure communication.
• Root Certificates: Issued by the CA and used to verify the authenticity of certificates issued to clients and servers.

1. Certificate Workflow:

• Client to API Server: When a client (like kubectl) communicates with the API server, both the client and the server need certificates to establish a secure connection.
• Master Node to Worker Node: Communication between the master node and worker nodes also needs to be encrypted, requiring certificates for both ends.
• Component-to-Component Communication: Internal communications, such as between the API server and etcd (the key-value store), or between various controllers and schedulers, must also be secured with appropriate certificates.

Creating and Using Certificates in Kubernetes

1. Generating Certificates:

• Use tools like OpenSSL to generate private keys and certificate signing requests (CSRs).
• Example command to generate a private key

openssl genrsa -out adam.key 2048

• Example command to create a CSR

openssl req -new -key adam.key -out adam.csr

1. Creating a Certificate Signing Request (CSR) in Kubernetes:

• Define a CSR in YAML format to submit to the Kubernetes API server.
• Example YAML for a CSR:

apiVersion: certificates.k8s.io/v1
kind: CertificateSigningRequest
metadata:
  name: adam
spec:
  request: <base64-encoded-csr>
  usages:
    - digital signature
    - key encipherment
    - server auth

• Apply the CSR using kubectl:

kubectl apply -f csr.yaml

1. Approving the CSR:

• As an administrator, approve the CSR using:

kubectl certificate approve adam

1. Distributing Certificates:

Once approved, you can retrieve the issued certificate and share it with the user. Decode the certificate if needed:

kubectl get csr adam -o yaml

Summary

In this blog, we’ve covered the essentials of SSL/TLS in Kubernetes, including how to generate and manage certificates for securing communications between various components of a Kubernetes cluster. Understanding these concepts is crucial for maintaining the security of your Kubernetes environments.

Thank you for following along with Day 21 of CK2024. Stay tuned for more in-depth coverage of Kubernetes concepts and practices. Happy learning, and see you in the next post!

For further reference, check out the detailed YouTube video here: