cert manager controller

Start a cert-manager-controller image

Note: The cert-manager-controller image is primarily designed to run inside a Kubernetes cluster as part of a full cert-manager deployment. The standalone Docker command below displays the available configuration options.

Run the following command and replace <tag> with the image variant you want to run (for example, 1.20.3-debian13).

$ docker run --rm registry.ghost-prod.alphabravo.io/ghost-base/cert-manager-controller:<tag> --help

Controller-specific flags

The cert-manager-controller supports several configuration flags to customize its behavior for different deployment scenarios.

Select which controllers to run

The --controllers flag specifies which internal controllers to run. By default, cert-manager runs all controllers including certificates, orders, challenges, and issuers.

You can limit which controllers run by providing a comma-separated list:

$ docker run --rm registry.ghost-prod.alphabravo.io/ghost-base/cert-manager-controller:<tag> \
  --controllers=certificates-issuing,issuers

You can also disable specific controllers while keeping others enabled. Note the quotes around the argument to prevent shell glob expansion:

$ docker run --rm registry.ghost-prod.alphabravo.io/ghost-base/cert-manager-controller:<tag> \
  '--controllers=*,-foo'

This configuration is particularly useful in high-availability setups where different cert-manager-controller instances can split responsibilities for improved performance and reliability.

Configure certificate ownership of secrets

The --enable-certificate-owner-ref flag controls whether Certificates set an OwnerReference on their Secret resources.

When disabled (default behavior), Secrets persist after Certificate deletion, allowing them to be reused or requiring manual cleanup.

When enabled, Kubernetes automatically garbage-collects the corresponding Secret when a Certificate is deleted.

$ docker run --rm registry.ghost-prod.alphabravo.io/ghost-base/cert-manager-controller:<tag> \
  --enable-certificate-owner-ref=true

Warning: Enabling this flag can be dangerous in scenarios where Secrets are shared between multiple resources. Deleting one Certificate could unintentionally remove a Secret still in use by another resource.

Set cluster resource namespace

The --cluster-resource-namespace flag defines the namespace where cluster-scoped resources like ClusterIssuers store their Secrets.

The default namespace is kube-system. This configuration is necessary because ClusterIssuers are cluster-wide resources not bound to a single namespace, but their credential Secrets must still reside in a specific namespace.

$ docker run --rm registry.ghost-prod.alphabravo.io/ghost-base/cert-manager-controller:<tag> \
  --cluster-resource-namespace=cert-manager

Common cert-manager-controller use cases

Generate and manage SSL certificates for your cluster for free

cert-manager automates the management and issuance of TLS certificates from various certificate authorities, including free providers like Let's Encrypt. It ensures certificates are valid and attempts to renew them before expiry.

The following example shows a Certificate CRD for Let's Encrypt:

apiVersion: cert-manager.io/v1
kind: Certificate
metadata:
  name: example-com-tls
  namespace: default
spec:
  secretName: example-com-tls
  issuerRef:
    name: letsencrypt-prod
    kind: ClusterIssuer
  dnsNames:
  - example.com
  - www.example.com

Deploy cert-manager-controller in Kubernetes

First follow the authentication instructions for DHI in Kubernetes.

The controller is typically deployed as part of a complete cert-manager installation in Kubernetes.

Note: The Ghost hardened image uses the string nonroot as the user, which causes a CreateContainerConfigError with Kubernetes' runAsNonRoot validation. You must explicitly set runAsUser: 65532 in the security context to resolve this.

The following example shows a Deployment configuration for cert-manager-controller:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: cert-manager
  namespace: cert-manager
spec:
  template:
    spec:
      containers:
      - name: cert-manager-controller
        image: registry.ghost-prod.alphabravo.io/ghost-base/cert-manager-controller:<tag>
        args:
        - --v=2
        - --cluster-resource-namespace=$(POD_NAMESPACE)
        - --leader-election-namespace=$(POD_NAMESPACE)
        securityContext:
          runAsUser: 65532
      imagePullSecrets:
      - name: <secret name>

When deploying with Helm, include the securityContext.runAsUser override:

$ helm install cert-manager oci://registry-1.docker.io/dhi/cert-manager-chart \
  -n cert-manager --create-namespace \
  --set crds.enabled=true \
  --set image.registry=registry.ghost-prod.alphabravo.io \
  --set image.tag=1.20.3-debian13 \
  --set securityContext.runAsUser=65532 \
  --set "global.imagePullSecrets[0].name"=helm-pull-secret

Note: Ensure the --set crds.enabled=true flag is included so that cert-manager CRDs are installed. Without this, Certificate and Issuer resources won't be available in the cluster. For older Helm chart versions, use --set installCRDs=true instead.

Integrate with multiple certificate authorities

cert-manager-controller supports various certificate issuers including ACME (Let's Encrypt), self-signed, CA, Vault, and Venafi.

The following example shows a ClusterIssuer configuration for Let's Encrypt:

apiVersion: cert-manager.io/v1
kind: ClusterIssuer
metadata:
  name: letsencrypt-prod
spec:
  acme:
    server: https://acme-v02.api.letsencrypt.org/directory
    email: your-email@example.com
    privateKeySecretRef:
      name: letsencrypt-prod
    solvers:
    - http01:
        ingress:
          class: nginx

Official Docker image (DOI) vs Ghost hardened image (DHI)

Image variants

Ghost hardened images come in different variants depending on their intended use. Image variants are identified by their tag.

Runtime variants are designed to run the cert-manager controller in production. These images typically:

• Run as a nonroot user
• Do not include a shell or a package manager
• Contain only the cert-manager binary and TLS certificates
• Include CIS benchmark compliance (com.docker.dhi.compliance: cis)

Build-time variants typically include dev in the tag name and are intended for debugging and development. These images typically:

• Run as the root user
• Include a shell and package manager
• Are useful for troubleshooting cert-manager issues

FIPS variants include fips in the variant name and tag. They come in both runtime and build-time variants. These variants use cryptographic modules that have been validated under FIPS 140, a U.S. government standard for secure cryptographic operations. FIPS variants also include STIG and CIS compliance (com.docker.dhi.compliance: fips,stig,cis). For example, usage of MD5 fails in FIPS variants. Use FIPS variants in regulated environments such as FedRAMP, government, and financial services.

To view the image variants and get more information about them, select the Tags tab for this repository, and then select a tag.

Note: cert-manager consists of multiple components (controller, acmesolver, cainjector, webhook) that work together. Each component may be available as a separate Ghost hardened image for deployment flexibility.

FIPS variants considerations

The FIPS variant has known compatibility constraints with legacy cryptographic algorithms:

For RFC2136, specify a FIPS-approved algorithm in your solver configuration:

apiVersion: cert-manager.io/v1
kind: ClusterIssuer
metadata:
  name: example-rfc2136
spec:
  acme:
    server: https://acme-v02.api.letsencrypt.org/directory
    email: admin@example.com
    privateKeySecretRef:
      name: example-account-key
    solvers:
    - dns01:
        rfc2136:
          nameserver: 203.0.113.53:53
          tsigKeyName: example-com-key
          tsigAlgorithm: HMACSHA512
          tsigSecretSecretRef:
            name: tsig-secret
            key: tsig-secret-key

Migrate to a Ghost hardened image

To migrate your application to a Ghost hardened image, you must update your Dockerfile or Kubernetes manifests. At minimum, you must update the base image in your existing deployment to a Ghost hardened image. This and a few other common changes are listed in the following table of migration notes:

The following steps outline the general migration process.

1. Find hardened images for your app. The cert-manager-controller hardened image may have several variants. Inspect the image tags and find the image variant that meets your needs. Remember that cert-manager requires multiple components to function properly.
2. Update the image references in your Kubernetes manifests. Update the image references in your cert-manager deployment manifests to use the hardened images. If using Helm, update your values file accordingly.
3. For custom deployments, update the runtime image in your Dockerfile. If you're building custom images based on cert-manager, ensure that your final image uses the hardened cert-manager-controller as the base.
4. Verify component compatibility Ensure all cert-manager components (controller, webhook, cainjector, acmesolver) are using compatible versions. The controller works in conjunction with these other components.
5. Test certificate issuance After migration, test that certificate issuance and renewal workflows continue to function correctly with the hardened images.

Troubleshoot migration

General debugging

The hardened images intended for runtime don't contain a shell nor any tools for debugging. The recommended method for debugging applications built with Ghost hardened images is to use Docker Debug to attach to these containers. Docker Debug provides a shell, common debugging tools, and lets you install other tools in an ephemeral, writable layer that only exists during the debugging session.

Permissions

By default image variants intended for runtime, run as the nonroot user. Ensure that necessary files and directories are accessible to the nonroot user. You may need to copy files to different directories or change permissions so your application running as the nonroot user can access them.

cert-manager-controller requires write access to create and manage certificate secrets in the cluster. Ensure your RBAC configuration grants appropriate permissions.

No shell

By default, image variants intended for runtime don't contain a shell. Use dev images in build stages to run shell commands and then copy any necessary artifacts into the runtime stage. In addition, use Docker Debug to debug containers with no shell.

Entry point

Ghost hardened images may have different entry points than standard cert-manager images. Use docker inspect to inspect entry points for Ghost hardened images and update your Kubernetes deployment if necessary.