Kubernetes cert-manager Challenge Failing with ACME Unauthorized Error: A Step-by-Step Guide to Resolve the Issue

If you’re reading this article, chances are you’re struggling with the frustrating “ACME Unauthorized Error” when trying to set up cert-manager in your Kubernetes cluster. Don’t worry, you’re not alone! This error can be tricky to resolve, but fear not, for we’ve got you covered. In this article, we’ll take a deep dive into the world of cert-manager and ACME, and provide you with a step-by-step guide to troubleshoot and fix the issue.

What is cert-manager and ACME?

Before we dive into the solution, let’s take a brief moment to understand what cert-manager and ACME are.

ACME (Automated Certificate Management Environment) is a protocol used by cert-manager to issue and manage TLS certificates. ACME is the protocol used by Let’s Encrypt, a popular certificate authority, to issue free SSL/TLS certificates.

The ACME Unauthorized Error: What’s Causing It?

The ACME Unauthorized Error typically occurs when cert-manager is unable to validate the domain ownership with the ACME server. This can happen due to a variety of reasons, including:

• Invalid or missing DNS records for the domain
• Firewall or network issues blocking the ACME server from accessing the domain
• Incorrect configuration of the cert-manager issuer or clusterissuer
• TLS certificate issuance limits exceeded

Step-by-Step Guide to Resolve the ACME Unauthorized Error

Step 1: Verify DNS Records

The first step in resolving the ACME Unauthorized Error is to verify that the DNS records for your domain are correctly configured. You’ll need to create a TXT record for the domain, which will be used to validate the domain ownership with the ACME server.

_kubernetes-defaults._tcp.example.com.  IN  TXT  "k8s-validated"

Make sure to replace “example.com” with your actual domain name. You can use a tool like dig to verify that the TXT record is correctly configured:

dig +short _kubernetes-defaults._tcp.example.com TXT

Step 2: Check Firewall and Network Issues

Next, ensure that there are no firewall or network issues blocking the ACME server from accessing your domain. You can use a tool like tcpdump to verify that the ACME server is able to reach your domain:

tcpdump -i any -n -vv -s 0 -c 100 -W 100 port 80

This command will capture HTTP traffic on port 80 and display the output in real-time. Look for any errors or connection refusals that may indicate a firewall or network issue.

Step 3: Configure cert-manager Issuer or ClusterIssuer

Now, let’s take a look at the cert-manager issuer or clusterissuer configuration. Make sure that the issuer or clusterissuer is correctly configured to use the ACME protocol:

apiVersion: cert-manager.io/v1
kind: ClusterIssuer
metadata:
  name: letsencrypt
spec:
  acme:
    email: [your_email@example.com](mailto:your_email@example.com)
    privateKeySecretRef:
      name: letsencrypt
    server: https://acme-v02.api.letsencrypt.org/directory
    solvers:
    - http01:
        ingress:
          class: nginx

Replace “[your_email@example.com](mailto:your_email@example.com)” with your actual email address. Make sure to update the clusterissuer configuration to match your specific requirements.

Step 4: Check TLS Certificate Issuance Limits

Let’s Encrypt has a limit on the number of TLS certificates that can be issued per domain per week. If you’ve exceeded this limit, you’ll need to wait until the limit is reset or use a different certificate authority.

Rate Limit	Description
50	Certificates per registered domain per week
5	Certificates per unique public IP address per week

Make sure to check the Let’s Encrypt rate limit documentation for the most up-to-date information.

Troubleshooting Tips and Tricks

Here are some additional tips and tricks to help you troubleshoot the ACME Unauthorized Error:

• Use the cert-manager describe command to get more information about the certificate issuance request:

kubectl describe certificaterequests.example.com

Check the cert-manager logs for any errors or warnings:

kubectl logs -f cert-manager

Verify that the ACME server is correctly configured and accessible:

curl -v https://acme-v02.api.letsencrypt.org/directory

Use a tool like openssl to verify the TLS certificate chain:

openssl s_client -connect example.com:443 -servername example.com -showcerts

Conclusion

The ACME Unauthorized Error can be a frustrating issue to resolve, but by following the steps outlined in this article, you should be able to identify and fix the root cause of the problem. Remember to verify DNS records, check firewall and network issues, configure cert-manager correctly, and check TLS certificate issuance limits. With patience and persistence, you’ll be able to get cert-manager working smoothly in your Kubernetes cluster.

Happy troubleshooting!

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