Overview of Let's Encrypt and Kubernetes Ingress Controller

Let's Encrypt is a renowned Certificate Authority (CA) that offers SSL/TLS certificates for free, which are essential for securing websites. Kubernetes, a powerful container orchestration platform, leverages ingress controllers to manage external access to services within a cluster. An ingress controller can automatically provision and manage SSL/TLS certificates, usually through Let's Encrypt, to secure the traffic.

However, in some cases, Kubernetes environments can encounter issues where fake or self-signed certificates are issued instead of genuine Let's Encrypt certificates. This article delves into this phenomenon, providing a technical exploration and remediation steps.

Role of Ingress Controllers in Certificate Issuance

In Kubernetes, an ingress controller is employed to expose HTTP and HTTPS routes from outside the cluster to services within the cluster. It directs external traffic to the appropriate services, typically defined via Kubernetes ingress resources.

There are several popular ingress controllers, such as:

• NGINX Ingress Controller
• Traefik
• Istio
• HAProxy

These controllers can be configured to automatically obtain SSL/TLS certificates from Let's Encrypt using the ACME (Automatic Certificate Management Environment) protocol, a critical step in automating secure communication.

Technical Workflow

The typical workflow for automatic certificate issuance via an ingress controller involves:

1. Ingress Resource Deployment: An ingress resource, specifying domain and path routes, is created in Kubernetes.
2. ACME Challenge: The ingress controller communicates with Let's Encrypt, usually performing a HTTP-01 challenge, to prove domain ownership. The challenge response is served by backing services.
3. Certificate Issuance: If the challenge is successful, Let's Encrypt issues a certificate which is stored in Kubernetes, often in a secret.
4. SSL Termination: The ingress controller uses the certificate to terminate SSL at the ingress point, ensuring encrypted traffic.

Fake Certificates: Causes and Implications

Occasionally, users experience scenarios where ingress controllers seemingly issue fake or self-signed certificates, resulting in browser warnings and potential security vulnerabilities. This can be attributed to one or more issues, such as:

1. Misconfiguration: Incorrect settings in ingress resources or ingress controller configurations might lead to self-signed certificates as fallback.
2. ACME Challenge Failures: Failures during Let's Encrypt verification might cause the ingress controller to default to self-signed certificates.
3. Resource Limitations: Constraints like lack of access permissions or networking issues can impede the ACME protocol's function.
4. Rate Limiting or Throttling: Let's Encrypt imposes rate limits on certificate requests. Exceeding these limits can result in provision of temporary certificates if no retries are scheduled.

Technical Example

Consider an NGINX Ingress Controller instance wherein a self-signed certificate is issued. A common config issue could be in the ingress.yaml file:

• hosts:
  • example.com
• host: example.com
  • path: /