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KCert: A Simple Let's Encrypt Cert Manager for Kubernetes

KCert is a simple alternative to cert-manager:

  • Deploys with around 100 lines of yaml (vs. thousands of lines for cert-manager)
  • Does not create or need any CRDs (Custom Resource Definitions) to operate
  • Runs a single service in your cluster, isolated in its own namespace

How it Works

  • KCert runs as a single-replica deployment in your cluster
  • An ingress is managed to route .acme/challenge requests to the service
  • Service provides a web UI for basic information and configuration details
  • Checks for certificates needing renewal every 6 hours
  • Automatically renews certificates with less than 30 days of validity
  • Watches for created and updated ingresses in the cluster
  • Automatically creates certificates for ingresses with the kcert.dev/ingress=managed label

Installing KCert

Deploy with Helm

First, add the Helm repo with: helm repo add nabsul https://nabsul.github.io/helm.

Then install with the following command (filling in your details):

kubectl create ns kcert
helm install kcert nabsul/kcert -n kcert --debug --set acmeTermsAccepted=true,acmeEmail=[YOUR EMAIL]

Note: This defaults to running KCert against Let's Encrypt's staging environment. After you've tested against staging, you can switch to production with:

helm install kcert nabsul/kcert -n kcert --debug --set acmeTermsAccepted=true,acmeEmail=[YOUR EMAIL],acmeDirUrl=https://acme-v02.api.letsencrypt.org/directory

For setting up SMTP email notifications and other parameters, please check the charts/kcert/values.yaml file and set the values under smtp accordingly. The SMTP password must be stored in a secret. If you stick with the defaults, you can simply create that secret with the following command:

kubectl create secret -n [YOUR NAMESPACE] generic kcert-smpt-secret --from-literal=password=[YOUR PASSWORD]

Creating a Certificate via Ingress

KCert automatically looks for ingresses that reference a certicate. If that certificate doesn't exist, it will create it (and renew it). KCert only monitors ingresses with the kcert.dev/ingress: "managed" label. You can either create your own ingress manually, or use the kcert-ingress chart:

helm install myingress1 nabsul/kcert-ingress -n kcert --debug --set name=[INGRESS_NAME],host=[DOMAIN],service=[SERVICE_NAME],port=[SERVICE_PORT]

Creating a Certificate via ConfigMap

If you want to create a certificate without creating an ingress, you can do so via a ConfigMap. You can create one using the kcert-configmap chart as follows:

helm install [VERSION] nabsul/kcert-configmap -n kcert --debug --set name=kcert,hosts=[HOSTS]

An example would be helm install 1.1.0 nabsul/kcert-configmap -n kcert --debug --set name=kcert,hosts="www.yourdomain.duckdns.org"

Namespace-constrained installations

If you are using Rancher clusters and are assigned a specific namespace without access to cluster-wide resources, it is possible to instruct KCert to query only a list of namespaces.

To enable the namespace-constrained mode, set the environment variable KCERT__NAMESPACECONSTRAINTS to a list of namespaces, separated by ",". Example: KCERT__NAMESPACECONSTRAINTS=ns-1,ns-2,ns-3.

Helm Charts

Check resulting yaml files without deploying:

helm template kcert-test .\charts\kcert --values .\temp\kcert-values.yaml

Other Advice

Test in Staging First

If this is your first time using KCert you should probably start out with https://acme-staging-v02.api.letsencrypt.org/directory. Experiment and make sure everything is working as expected, then switch over to https://acme-v02.api.letsencrypt.org/directory. More information this topic can be found here.

Using EAB (External Account Binding)

KCert supports the EAB authentication protocol for providers requiring it. To set it up, set the following environment variables:

ACME__EABKEYID: Key identifier given by your ACME provider
ACME__EABHMACKEY: HMAC key given by your ACME provider

Diagnostics

To check that everything is running as expected:

  • Run kubectl -n kcert logs svc/kcert and make sure there are no error messages
  • Run kubectl -n kcert port-forward svc/kcert 8080 and go to http://localhost:8080 in your browser

Testing SMTP Configuration

To test your email configuration you can connect to the KCert dasboard by running kubectl -n kcert port-forward svc/kcert 8080 and opening http://localhost:8080 in your browser. From there, navigate to the configuration section. Check that your settings are listed there, and then click "Send Test Email" to receive a test email.

Optional: Configure a fixed ACME Key

By default KCert will generate a random secret key at startup. For many use cases this will be fine. If you would like to use a fixed key, you can provide it as an environment variable.

You can generate your own random key with the following:

docker run -it nabsul/kcert:v1.0.1 dotnet KCert.dll generate-key

Next you would need to put that generated key into a Kubernetes secret:

kubectl -n kcert create secret generic kcert-key --from-literal=key=[...]

Finally, add this to your deployment's environment variables:

        - name: ACME__KEY
          valueFrom:
            secretKeyRef:
              name: kcert-key
              key: key

Creating Certificates

KCert watches for changes to ingresses in cluster and reacts to them accordingly. KCert will ignore an ingress unless it is labelled with kcert.dev/ingress=managed. For example, you could configure an ingress as follows:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: test1-ingress
  labels:
    kcert.dev/ingress: "managed"
  annotations:
    kubernetes.io/ingress.class: "nginx"
spec:
  tls:
  - hosts:
    - test1.kcert.dev
    - test2.kcert.dev
    secretName: test1-tls
  rules:
  - host: test1.kcert.dev
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: hello-world
            port:
              number: 80
  - host: test2.kcert.dev
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: hello-world
            port:
              number: 80

KCert should automatically detect this new ingress and generate a TLS secret called test1-tls for the two domains listed above. You could also create one certificate per host as follows:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: test1-ingress
  labels:
    kcert.dev/ingress: "managed"
  annotations:
    kubernetes.io/ingress.class: "nginx"
spec:
  tls:
  - hosts:
    - test1.kcert.dev
    secretName: test1-tls
  tls:
  - hosts:
    - test2.kcert.dev
    secretName: test2-tls
  rules:
  - host: test1.kcert.dev
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: hello-world
            port:
              number: 80
  - host: test2.kcert.dev
    http:
      paths:
      - path: /
        pathType: Prefix
        backend:
          service:
            name: hello-world
            port:
              number: 80

Automatic Certificate Renewal

Once every 6 hours KCert will check for certificates that are expiring in 30 days or less. It will attempt to automatically renew those certificates. If you have email notifications set up, you will receive a notifications of success of failure of the renewal process.

Further Configuration Settings

KCert uses the standard .NET Core configuration library to manage its settings. The appsettings.json contains the full list of settings with reasonable default values.

All settings shown in appsettings.json can be modified via environment variables. For example, you can override the value of the Acme:RenewalCheckTimeHours setting with a ACME__RENEWALCHECKTIMEHOURS environment variable. Note that there are two underscore (_) characters in between the two parts of the setting name. For more information see the official .NET Core documentation.

Building from Scratch

To build your own container image: docker build -t [your tag] .

Running Locally

For local development, I recommend using dotnet user-secrets to configure all of KCert's required settings. You can run KCert locally with dotnet run. KCert will use your local kubectl configuration to connect to a Kubernetes cluster. It will behave as if it is running in the cluster and you will be able to explore any settings that might be there.

Uninstalling KCert

KCert does not create many resources, and most of them are restricted to the kcert namespace. Removing KCert from your cluster is as simple as executing these three commands:

kubectl delete namespace kcert
kubectl delete clusterrolebinding kcert
kubectl delete clusterrole kcert

Note that certificates created by KCert in other namespaces will NOT be deleted. You can keep those certificates or manually delete them.