K8s gitlab-runner RBAC

Q:

What is the appropriate K8s RBAC resources to configure a gitlab-runner in namespace "gitlab-runner" that allows for deploying and managing workloads (pods, deployment, secrets, ...) but only in namespace "teams"

A:

To allow a gitlab-runner (in namespace gitlab-runner) to deploy and manage workloads such as Pods, Deployments, Secrets, etc., but only within the teams namespace, you need to:

✅ 1. Use a ServiceAccount in gitlab-runner namespace

This is the identity your GitLab Runner pods use.

apiVersion: v1
kind: ServiceAccount
metadata:
  name: gitlab-runner
  namespace: gitlab-runner

✅ 2. Create a Role in the teams namespace

This defines what actions are allowed within the teams namespace.

apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: gitlab-deployer
  namespace: teams
rules:
- apiGroups: ["", "apps", "batch"]
  resources: ["pods", "pods/log", "services", "secrets", "configmaps", "deployments", "replicasets", "jobs", "cronjobs"]
  verbs: ["get", "list", "watch", "create", "update", "patch", "delete"]

✅ 3. Create a RoleBinding in the teams namespace

This binds the service account in the gitlab-runner namespace to the role in teams.

apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: gitlab-deployer-binding
  namespace: teams
subjects:
- kind: ServiceAccount
  name: gitlab-runner
  namespace: gitlab-runner
roleRef:
  kind: Role
  name: gitlab-deployer
  apiGroup: rbac.authorization.k8s.io

Summary

💡 This setup ensures namespace isolation: the runner can only manage workloads in teams, even though it's running in gitlab-runner.

Additionally,

The gitlab-runner must be allowed to create resources in its own namespaces, so

# RoleBinding to bind that Role to the runner's ServiceAccount
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: gitlab-runner-job-binding
  namespace: gitlab-runner
subjects:
- kind: ServiceAccount
  name: gitlab-runner
  namespace: gitlab-runner
roleRef:
  kind: Role
  name: gitlab-runner-job-manager
  apiGroup: rbac.authorization.k8s.io

# Role for managing job pods and related resources in gitlab-runner namespace
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: gitlab-runner-job-manager
  namespace: gitlab-runner
rules:
- apiGroups: ["", "apps", "batch"]
  resources:
    - pods
    - pods/log
    - configmaps
    - secrets
    - services
    - jobs
  verbs: ["get", "list", "watch", "create", "update", "patch", "delete"]

How to protect the gitlab-runner then

That's an excellent and subtle insight — and here's the nuanced answer:

✅ Yes, you can protect the GitLab Runner controller from teams, but only if you separate execution and deployment namespaces — and don’t run ephemeral CI jobs in gitlab-runner.

🔄 Why You're Feeling Stuck

If:

• CI jobs (ephemeral runner pods) run in gitlab-runner, and
• Those pods run developer-supplied code (script: in .gitlab-ci.yml),

Then:

• You're giving developer-controlled pods access to the same namespace that holds the GitLab Runner controller, config, and ServiceAccount.

• Those pods can, unless otherwise blocked:

  • Mount the same ServiceAccount (if not using automountServiceAccountToken: false)
  • Read or patch shared ConfigMaps, Secrets, or even disrupt the controller

So yes — it's a real attack surface, and many don't realize this.

✅ Real Isolation Strategy

To truly isolate the GitLab Runner controller from developers, follow this model:

🧩 Runner controller in gitlab-runner namespace

• Long-lived Deployment
• Uses a ServiceAccount: gitlab-runner
• Only binds that SA with RBAC to target namespace(s), like teams

🧩 CI job pods run in a separate namespace (teams)

• You must configure the runner Helm chart to:

  runners:
  namespace: teams
  

• This causes job pods to spawn in teams

• Developers control teams, but have no access to gitlab-runner

✅ Net result:

Developers can:

• Deploy and manage in teams
• Write .gitlab-ci.yml that spawns jobs (in teams)

But cannot touch:

• The GitLab Runner controller pod
• Its ConfigMaps, Secrets, logs
• The Helm release or its ServiceAccount

🔥 Why Mixing Both in One Namespace is Dangerous

If ephemeral jobs run in the same namespace as the controller:

• Devs can kubectl get secrets or even exec into another pod, unless prevented
• You'd need complex policies to isolate pods from pods in the same namespace
• Even PodSecurityPolicy / PodSecurityAdmission can’t fully enforce RBAC-like isolation within a namespace

🛡 Additional Hardening (if needed)

• Set automountServiceAccountToken: false for CI jobs to prevent API access
• Use OPA/Gatekeeper to prevent pods in gitlab-runner from accessing runner resources
• Use Kubernetes NetworkPolicy to prevent job pods from talking to the controller pod

✅ TL;DR: You Can Isolate — but Only if:

• CI job pods run in a different namespace (e.g., teams)
• You do not run any dev-controlled code in the gitlab-runner namespace

values.yaml

To implement the above:

Here’s a secure and minimal values.yaml for the official GitLab Runner Helm chart, designed to:

✅ Goals:

• Deploy the GitLab Runner controller in namespace: gitlab-runner
• Ensure ephemeral job pods run in namespace: teams
• Use a ServiceAccount that only has RBAC permissions in teams
• Prevent CI job pods from touching anything in gitlab-runner

📄 values.yaml for GitLab Runner

## Runner registration
gitlabUrl: https://gitlab.example.com/
runnerRegistrationToken: "__REPLACE_ME__"

## Optional labels
runners:
  tags: ["k8s", "secure"]


  kubernetes:
    ## Don't automatically mount SA tokens in job pods (limit abuse)
    automountServiceAccountToken: false # Prevents the downward API from injecting the token

  ## Namespace where ephemeral CI job pods will run:
  namespace: teams

  podSecurityContext:
    runAsNonRoot: true
    runAsUser: 1000
  serviceAccountName: gitlab-runner

  ## Optional: Add limits to CI job pods
  resources:
    limits:
      memory: "512Mi"
      cpu: "500m"
    requests:
      memory: "256Mi"
      cpu: "250m"

  ## Optional: Job pod cleanup
  podAnnotations:
    cleanup.after.success: "true"
    cleanup.after.failure: "true"

## Install ServiceAccount in gitlab-runner namespace
serviceAccount:
  create: true
  name: gitlab-runner

## Optional: Use RBAC just for the namespace it runs jobs in
rbac:
  create: false  # We'll define custom RBAC externally — more secure

## Disable host-level mounts for security
metrics:
  enabled: false

🚀 How to Deploy This Securely

1. Create Namespace(s)

kubectl create namespace gitlab-runner
kubectl create namespace teams

2. Install Helm Chart

helm repo add gitlab https://charts.gitlab.io
helm repo update

helm upgrade --install gitlab-runner gitlab/gitlab-runner \
  -n gitlab-runner \
  -f values.yaml

3. Create RBAC for ServiceAccount (gitlab-runner) in teams

You must manually create the Role/RoleBinding to allow deployments in teams:

# role.yaml
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  namespace: teams
  name: gitlab-deployer
rules:
- apiGroups: ["", "apps", "batch"]
  resources: ["pods", "deployments", "replicasets", "services", "jobs", "cronjobs", "secrets", "configmaps", "persistentvolumeclaims"]
  verbs: ["get", "list", "watch", "create", "update", "patch", "delete"]
---
# rolebinding.yaml
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  namespace: teams
  name: gitlab-deployer-binding
subjects:
- kind: ServiceAccount
  name: gitlab-runner
  namespace: gitlab-runner
roleRef:
  kind: Role
  name: gitlab-deployer
  apiGroup: rbac.authorization.k8s.io

Apply it:

kubectl apply -f role.yaml
kubectl apply -f rolebinding.yaml

✅ What This Achieves

This is the secure separation you're aiming for. Let me know if you'd like to also:

• Use an external secret manager (e.g., Vault),
• Use imagePullSecrets or affinity rules,
• Block specific container images or commands in CI jobs.