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Using cert-manager to enroll certificate in Kubernetes environments

I don not really have a full kubernets environment. Thus, I was using https://microk8s.io/ for testing.

Prerequisites

  • cert-manager must be installed. See instructions for further information. (I was installing with regular manifest but did change to helm to ensure that I always use the latest version)

Issuer configuration

The below steps based on instructions taken from cert-manager documention. Cert-manager can run as Issuser or ClusterIssuer ressource. The below configuration example uses Issuer ressource; an ClusterIssuer configuration is part of the release regression testing both http-01 and dns-01 challenge validation.

  • Create an issuer configuration file as below
apiVersion: v1
kind: Namespace
metadata:
  name: cert-manager-acme
---
apiVersion: cert-manager.io/v1
kind: Issuer
metadata:
  name: acme2certifier
  namespace: cert-manager-acme
spec:
  acme:
    email: foo@bar.local
    server: http://192.168.14.1/directory
    privateKeySecretRef:
      # Secret resource that will be used to store the account's private key.
      name: issuer-account-key
    # Add a single challenge solver, HTTP01 using nginx
    solvers:
    - http01:
        ingress:
          class: nginx
---
apiVersion: cert-manager.io/v1
kind: Certificate
metadata:
  name: acme-cert
  namespace: cert-manager-acme
spec:
  secretName: k8-acme-secret
  issuerRef:
    name: acme2certifier
  dnsNames:
    - k8-acme.bar.local
  # optional but recommended to avoid reenrollment loops in case of short certificate lifetimes
  renewBefore: 48h
  • apply the configuration. Certificate enrollment should start immediately
grindsa@ub-20:~$ microk8s.kubectl apply -f acme2certifier.yaml
  • the enrollment status can be checked via microk8s.kubectl describe certificate -n cert-manager-acme
grindsa@ub-20:~$ microk8s.kubectl describe certificate -n cert-manager-acme
Name:         acme-cert
Namespace:    cert-manager-acme
Labels:       <none>
Annotations:  API Version:  cert-manager.io/v1alpha3
Kind:         Certificate
...
Spec:
  Dns Names:
    k8-acme.bar.local
  Issuer Ref:
    Name:       acme2certifier
  Secret Name:  acme2certifier-secret
Status:
  Conditions:
    Last Transition Time:  2020-06-28T07:36:05Z
    Message:               Certificate is up to date and has not expired
    Reason:                Ready
    Status:                True
    Type:                  Ready
  Not After:               2021-06-28T07:35:53Z
Events:
  Type    Reason        Age   From          Message
  ----    ------        ----  ----          -------
  Normal  GeneratedKey  60s   cert-manager  Generated a new private key
  Normal  Requested     60s   cert-manager  Created new CertificateRequest resource "acme-cert-3129588559"
  Normal  Issued        58s   cert-manager  Certificate issued successfully
  • the certificate details can be checked by using the command microk8s.kubectl get certificate acme-cert -o yaml -n cert-manager-acme
  • You can check the private key with microk8s.kubectl get secret acme-cert-key -o yaml -n cert-manager-acme. You should see a base64 encoded key in the tls.key field.
  • certificate, issuer and namespace can be deleted with microk8s.kubectl delete -f acme2certifier.yaml

Troubleshooting

There are extensive troubleshooting guides at the cert-manager website.

Below a list of commends I considered as most useful for me:

  • kubectl get order -n <name-space> - to get the list of orders
  • kubectl describe order -n <name-space> <order> - to display the details of an order
  • kubectl describe challenge -n <name-space> - show challenges and provisioning status