Existing Cluster Install: Using Custom RBAC roles

dex
Tue, 19 Jul 2022 12:55:09 +0000
Supporting your customers

Question from this week about using custom / BYO RBAC roles when installing App Manager (KOTS) into an existing kubernetes cluster – specifically Openshift in this case.

Our Openshift cluster has a built-in role admin that we’d like to use instead of the role created by kubectl kots install --use-minimal-rbac or oc kots install --use-minimal-rbac. Because the admin account permissions are slightly more narrow than the kots-created RBAC role, the installation fails if a user with the admin role attempts to perform an installation. Is there a way to have the App Manager workloads use this admin account instead of creating a new one with " * * * " permissions on the namespace / project?

Solution

Credit goes to @bco for this solution. Thanks Barry!

Disclaimer - This is an advanced topic and a deep dive on the nuances of Kubernetes RBAC is beyond the scope of this post. The viability of this workaround depends on the admin role in this example having equivalent or very nearly equivalent * * * permissions to every object in the target namespace, similar to the the default role created when --minimal-rbac is used. If the target role has insufficient permissions, this may result in a totally broken installation. App Manager needs these permissions to create, update, and destroy all managed objects in the target namespace.

Manually Creating RBAC objects

We’ll pre-create an RBAC ServiceAccount and RoleBinding, then use --use-minimal-rbac along with --skip-rbac-check and --ensure-rbac=false to perform the install.

# rbac.yaml - change namespace and roleRef as desired
apiVersion: v1
kind: ServiceAccount
metadata:
  labels:
    kots.io/kotsadm: "true"
  name: kotsadm
  namespace: my-app
---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  labels:
    kots.io/kotsadm: "true"
  name: kotsadm-rolebinding
  namespace: my-app
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: ClusterRole
  name: admin
subjects:
- kind: ServiceAccount
  name: kotsadm
  namespace: my-app

Once these are created, run the kubectl kots install or oc kots install command with the appropriate flags. The below is for an installation into an airgapped openshift cluster using a private registry at private.registry.host.

oc kots install my-app \
  --namespace my-app \
  --license-file ./license.yaml \
  --airgap-bundle /path/to/application.airgap \
  --kotsadm-namespace my-app \
  --kotsadm-registry private.registry.host \
  --registry-username rw-username \
  --registry-password rw-password \
  --use-minimal-rbac \
  --skip-rbac-check \
  --ensure-rbac=false

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