Syncing Secrets Across Namespaces

It may be required for multiple components across namespaces to consume the same Secret that has been created by a single Certificate. The recommended way to do this is to use kubed with its secret syncing feature. However if your use case is a wildcard certificate another approach may meet your needs.

Serving a wildcard to ingress resources in different namespaces (default SSL certificate)

Most ingress controllers, including ingress-nginx, Traefik, and Kong support specifying a single certificate to be used for ingress resources which request TLS but do not specify tls.[].secretName. This is often referred to as a "default SSL certificate". As long as this is correctly configured, ingress resources in any namespace will be able to use a single wildcard certificate. Wildcard certificates are not supported with HTTP01 validation and require DNS01.

Sample ingress snippet:

apiVersion: networking.k8s.io/v1beta1
kind: Ingress
#[...]
spec:
  rules:
  - host: service.example.com
  #[...]
  tls:
  - hosts:
    - service.example.com
    #secretName omitted to use default wildcard certificate

Syncing arbitrary secrets across namespaces using kubed

In order for the target Secret to be synced, the Secret resource must first be created with the correct annotations before the creation of the Certificate, else the Secret will need to be edited instead. The example below shows syncing a certificate belonging to the sandbox Certificate from the cert-manager namespace, into the sandbox namespace.

apiVersion: v1
kind: Namespace
metadata:
  name: sandbox
  labels:
    cert-manager-tls: sandbox # Define namespace label for kubed
---
apiVersion: v1
data:
  ca.crt: ''
  tls.crt: ''
  tls.key: ''
kind: Secret
metadata:
  name: sandbox-tls
  namespace: cert-manager
  annotations:
    kubed.appscode.com/sync: "cert-manager-tls=sandbox" # Sync certificate to matching namespaces
type: kubernetes.io/tls
---
apiVersion: cert-manager.io/v1
kind: Certificate
metadata:
  name: sandbox
  namespace: cert-manager
spec:
  secretName: sandbox-tls
  commonName: sandbox
  issuerRef:
    name: sandbox-ca
    kind: Issuer
    group: cert-manager.io