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trusted-tls-for-control-planes.md

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Trusted TLS certificate for shoot control planes

Shoot clusters are composed of several control plane components deployed by the Gardener and corresponding extensions.

Some components are exposed via Ingress resources which make them addressable under the HTTPS protocol.

Examples:

  • Alertmanager
  • Grafana for operators and end-users
  • Prometheus
  • Kibana

Gardener generates the backing TLS certificates which are signed by the shoot cluster's CA by default (self-signed).

Unlike with a self-contained Kubeconfig file, common internet browsers or operating systems don't trust a shoot's cluster CA and adding it as a trusted root is often undesired in enterprise environments.

Therefore, Gardener operators can predefine trusted wildcard certificates under which the mentioned endpoints will be served instead.

Register a trusted wildcard certificate

Since control plane components are published under the ingress domain (core.gardener.cloud/v1beta1.Seed.spec.dns.ingressDomain) a wildcard certificate is required.

For example:

  • Seed ingress domain: dev.my-seed.example.com
  • CN or SAN for certificate: *.dev.my-seed.example.com

A wildcard certificate matches exactly one seed. It must be deployed as part of your landscape setup as a Kubernetes Secret inside the garden namespace of the corresponding seed cluster.

Please ensure that the secret has the gardener.cloud/role label shown below.

apiVersion: v1
data:
  ca.crt: base64-encoded-ca.crt
  tls.crt: base64-encoded-tls.crt
  tls.key: base64-encoded-tls.key
kind: Secret
metadata:
  labels:
    gardener.cloud/role: controlplane-cert
  name: seed-ingress-certificate
  namespace: garden
type: Opaque

Gardener copies the secret during the reconciliation of shoot clusters to the shoot namespace in the seed. Afterwards, Ingress resources in that namespace for the mentioned components will refer to the wildcard certificate.

Best practice

While it is possible to create the wildcard certificates manually and deploy them to seed clusters, it is recommended to let certificate management components do this job. Often, a seed cluster is also a shoot cluster at the same time (shooted seed) and might already provide a certificate service extension. Otherwise, a Gardener operator may use solutions like Cert-Management or Cert-Manager.