LetsEncrypt Issuers
Certificates are issued by certificate authorities. By far the most common issuer will be LetsEncrypt.
In order for Cert Manager to request/renew certificates, we have to tell it about our Issuers.
Note
There's a minor distinction between an Issuer (only issues certificates within one namespace) and a ClusterIssuer (issues certificates throughout the cluster). Typically a ClusterIssuer will be suitable.
Ingredients
- A Kubernetes cluster
- Flux deployment process bootstrapped
- Cert-Manager deployed to request/renew certificates
- API credentials for a supported DNS01 provider for LetsEncrypt wildcard certs
Preparation
Namespace
We need a namespace to deploy our certificates into. Per the flux design, I create this example yaml in my flux repo:
apiVersion: v1
kind: Namespace
metadata:
name: letsencrypt-wildcard-cert
Kustomization
Now we need a kustomization to tell Flux to install any YAMLs it finds in /letsencrypt-wildcard-cert. I create this example Kustomization in my flux repo:
apiVersion: kustomize.toolkit.fluxcd.io/v1
kind: Kustomization
metadata:
name: letsencrypt-wildcard-cert
namespace: flux-system
spec:
interval: 15m
path: ./letsencrypt-wildcard-cert
dependsOn:
- name: "cert-manager"
- name: "sealed-secrets"
prune: true # remove any elements later removed from the above path
timeout: 2m # if not set, this defaults to interval duration, which is 1h
sourceRef:
kind: GitRepository
name: flux-system
Tip
Importantly, note that we define a dependsOn, to tell Flux not to try to reconcile this kustomization before the cert-manager and sealedsecrets kustomizations are reconciled. Cert-manager creates the CRDs used to define certificates, so prior to Cert Manager being installed, the cluster won't know what to do with the ClusterIssuers/Certificate resources.
LetsEncrypt Staging
The ClusterIssuer resource below represents a certificate authority which is able to request certificates for any namespace within the cluster. I save this in my flux repo as illustrated below. I've highlighted the areas you'll need to pay attention to:
apiVersion: cert-manager.io/v1
kind: ClusterIssuer
metadata:
name: letsencrypt-staging
spec:
acme:
email: batman@example.com
server: https://acme-staging-v02.api.letsencrypt.org/directory
privateKeySecretRef:
name: letsencrypt-staging
solvers:
- selector:
dnsZones:
- "example.com"
dns01:
cloudflare:
email: batman@example.com
apiTokenSecretRef:
name: cloudflare-api-token-secret
key: api-token
Deploying this issuer YAML into the cluster would provide Cert Manager with the details necessary to start issuing certificates from the LetsEncrypt staging server (always good to test in staging first!)
Note
The example above is specific to Cloudflare, but the syntax for other providers is similar.
LetsEncrypt Prod
As you'd imagine, the "prod" version of the LetsEncrypt issues is very similar, and I save this in my flux repo:
apiVersion: cert-manager.io/v1
kind: ClusterIssuer
metadata:
name: letsencrypt-prod
spec:
acme:
email: batman@example.com
server: https://acme-v02.api.letsencrypt.org/directory
privateKeySecretRef:
name: letsencrypt-prod
solvers:
- selector:
dnsZones:
- "example.com"
dns01:
cloudflare:
email: batman@example.com
apiTokenSecretRef:
name: cloudflare-api-token-secret
key: api-token
Note
You'll note that there are two secrets referred to above - privateKeySecretRef, referencing letsencrypt-prod is for cert-manager to populate as a result of its ACME schenanigans - you don't have to do anything about this particular secret! The cloudflare-specific secret (and this will change based on your provider) is expected to be found in the same namespace as the cert-manager itself, and will be discussed when we create our wildcard certificate.
Serving
How do we know it works?
We're not quite ready to issue certificates yet, but we can now test whether the Issuers are configured correctly for LetsEncrypt. To check their status, describe the ClusterIssuers (i.e., kubectl describe clusterissuer letsencrypt-prod), which (truncated) shows something like this:
Status:
Acme:
Last Registered Email: admin@example.com
Uri: https://acme-v02.api.letsencrypt.org/acme/acct/34523
Conditions:
Last Transition Time: 2021-11-18T22:54:20Z
Message: The ACME account was registered with the ACME server
Observed Generation: 1
Reason: ACMEAccountRegistered
Status: True
Type: Ready
Events: <none>
Provided your account is registered, you're ready to proceed with creating a wildcard certificate!
Chef's notes 📓
-
Since a ClusterIssuer is not a namespaced resource, it doesn't exist in any specific namespace. Therefore, my assumption is that the
apiTokenSecretRefsecret is only "looked for" when a certificate (which is namespaced) requires validation. ↩
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