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Manage certificates with Gardener for default domain

Introduction

Dealing with applications on Kubernetes which offer a secure service endpoints (e.g. HTTPS) also require you to enable a secured communication via SSL/TLS. With the certificate extension enabled, Gardener can manage commonly trusted X.509 certificate for your application endpoint. From initially requesting certificate, it also handeles their renewal in time using the free Let’s Encrypt API.

There are two senarios with which you can use the certificate extension

You want to use a certificate for a subdomain the shoot’s default DNS (see .spec.dns.domain of your shoot resource, e.g. short.ingress.shoot.project.default-domain.gardener.cloud). If this is your case, please keep reading this article.
You want to use a certificate for a custom domain. If this is your case, please see Manage certificates with Gardener for public domain

Prerequisites

Before you start this guide there are a few requirements you need to fulfill:

You have an existing shoot cluster

Since you are using the default DNS name, all DNS configuration should already be done and ready.

Issue a certificate

Every X.509 certificate is represented by a Kubernetes custom resource certificate.cert.gardener.cloud in your cluster. A Certificate resource may be used to initiate a new certificate request as well as to manage its lifecycle. Gardener’s certificate service regularly checks the expiration timestamp of Certificates, triggers a renewal process if necessary and replaces the existing X.509 certificate with a new one.

Your application should be able to reload replaced certificates in a timely manner to avoid service disruptions.

Certificates can be requested via 3 resources type

Ingress
Service (type LoadBalancer)
certificate (Gardener CRD)

If either of the first 2 are used, a corresponding Certificate resource will automatically be created.

Using an ingress Resource

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: amazing-ingress
  annotations:
    cert.gardener.cloud/purpose: managed
    #cert.gardener.cloud/issuer: custom-issuer                    # optional to specify custom issuer (use namespace/name for shoot issuers)
    #cert.gardener.cloud/follow-cname: "true"                     # optional, same as spec.followCNAME in certificates
    #cert.gardener.cloud/secret-labels: "key1=value1,key2=value2" # optional labels for the certificate secret
    #cert.gardener.cloud/preferred-chain: "chain name"            # optional to specify preferred-chain (value is the Subject Common Name of the root issuer)
    #cert.gardener.cloud/private-key-algorithm: ECDSA             # optional to specify algorithm for private key, allowed values are 'RSA' or 'ECDSA'
    #cert.gardener.cloud/private-key-size: "384"                  # optional to specify size of private key, allowed values for RSA are "2048", "3072", "4096" and for ECDSA "256" and "384"spec:
  tls:
  - hosts:
    # Must not exceed 64 characters.
    - short.ingress.shoot.project.default-domain.gardener.cloud
    # Certificate and private key reside in this secret.
    secretName: tls-secret
  rules:
  - host: short.ingress.shoot.project.default-domain.gardener.cloud
    http:
      paths:
      - pathType: Prefix
        path: "/"
        backend:
          service:
            name: amazing-svc
            port:
              number: 8080

Using a service type LoadBalancer

apiVersion: v1
kind: Service
metadata:
  annotations:
    cert.gardener.cloud/purpose: managed
    # Certificate and private key reside in this secret.
    cert.gardener.cloud/secretname: tls-secret
    # You may add more domains separated by commas (e.g. "service.shoot.project.default-domain.gardener.cloud, amazing.shoot.project.default-domain.gardener.cloud")
    dns.gardener.cloud/dnsnames: "service.shoot.project.default-domain.gardener.cloud" 
    dns.gardener.cloud/ttl: "600"
    #cert.gardener.cloud/issuer: custom-issuer                    # optional to specify custom issuer (use namespace/name for shoot issuers)
    #cert.gardener.cloud/follow-cname: "true"                     # optional, same as spec.followCNAME in certificates
    #cert.gardener.cloud/secret-labels: "key1=value1,key2=value2" # optional labels for the certificate secret
    #cert.gardener.cloud/preferred-chain: "chain name"            # optional to specify preferred-chain (value is the Subject Common Name of the root issuer)
    #cert.gardener.cloud/private-key-algorithm: ECDSA             # optional to specify algorithm for private key, allowed values are 'RSA' or 'ECDSA'
    #cert.gardener.cloud/private-key-size: "384"                  # optional to specify size of private key, allowed values for RSA are "2048", "3072", "4096" and for ECDSA "256" and "384"  name: test-service
  namespace: default
spec:
  ports:
    - name: http
      port: 80
      protocol: TCP
      targetPort: 8080
  type: LoadBalancer

Using the custom Certificate resource

apiVersion: cert.gardener.cloud/v1alpha1
kind: Certificate
metadata:
  name: cert-example
  namespace: default
spec:
  commonName: short.ingress.shoot.project.default-domain.gardener.cloud
  secretRef:
    name: tls-secret
    namespace: default
  # Optionnal if using the default issuer
  issuerRef:
    name: garden

If you’re interested in the current progress of your request, you’re advised to consult the description, more specifically the status attribute in case the issuance failed.

Request a wildcard certificate

In order to avoid the creation of multiples certificates for every single endpoints, you may want to create a wildcard certificate for your shoot’s default cluster.

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: amazing-ingress
  annotations:
    cert.gardener.cloud/purpose: managed
    cert.gardener.cloud/commonName: "*.ingress.shoot.project.default-domain.gardener.cloud"
spec:
  tls:
  - hosts:
    - amazing.ingress.shoot.project.default-domain.gardener.cloud
    secretName: tls-secret
  rules:
  - host: amazing.ingress.shoot.project.default-domain.gardener.cloud
    http:
      paths:
      - pathType: Prefix
        path: "/"
        backend:
          service:
            name: amazing-svc
            port:
              number: 8080

Please note that this can also be achived by directly adding an annotation to a Service type LoadBalancer. You could also create a Certificate object with a wildcard domain.

More information

For more information and more examples about using the certificate extension, please see Manage certificates with Gardener for public domain