Securing Your Cluster

Linkerd provides powerful introspection into your Kubernetes cluster and services. Linkerd installations are secure by default. This page illustrates best practices to enable this introspection in a secure way.

Tap

The default Linkerd installation includes Tap support. This feature is available via the following commands:

Depending on your RBAC setup, you may need to perform additional steps to enable your user(s) to perform Tap actions.

Check for Tap access

Use kubectl to determine whether your user is authorized to perform tap actions. For more information, see the Kubernetes docs on authorization.

To determine if you can watch pods in all namespaces:

kubectl auth can-i watch pods.tap.linkerd.io --all-namespaces

To determine if you can watch deployments in the emojivoto namespace:

kubectl auth can-i watch deployments.tap.linkerd.io -n emojivoto

To determine if a specific user can watch deployments in the emojivoto namespace:

kubectl auth can-i watch deployments.tap.linkerd.io -n emojivoto --as $(whoami)

You can also use the Linkerd CLI’s --as flag to confirm:

$ linkerd tap -n linkerd deploy/linkerd-controller --as $(whoami)
Error: HTTP error, status Code [403] (deployments.tap.linkerd.io "linkerd-controller" is forbidden: User "siggy" cannot watch resource "deployments/tap" in API group "tap.linkerd.io" in the namespace "linkerd")
...

Enabling Tap access

If the above commands indicate you need additional access, you can enable access with as much granularity as you choose.

Granular Tap access

To enable tap access to all resources in all namespaces, you may bind your user to the linkerd-linkerd-tap-admin ClusterRole, installed by default:

$ kubectl describe clusterroles/linkerd-linkerd-tap-admin
Name:         linkerd-linkerd-tap-admin
Labels:       linkerd.io/control-plane-component=tap
              linkerd.io/control-plane-ns=linkerd
Annotations:  kubectl.kubernetes.io/last-applied-configuration:
                {"apiVersion":"rbac.authorization.k8s.io/v1","kind":"ClusterRole","metadata":{"annotations":{},"labels":{"linkerd.io/control-plane-compone...
PolicyRule:
  Resources         Non-Resource URLs  Resource Names  Verbs
  ---------         -----------------  --------------  -----
  *.tap.linkerd.io  []                 []              [watch]

To bind the linkerd-linkerd-tap-admin ClusterRole to a particular user:

kubectl create clusterrolebinding \
  $(whoami)-tap-admin \
  --clusterrole=linkerd-linkerd-tap-admin \
  --user=$(whoami)

You can verify you now have tap access with:

$ linkerd tap -n linkerd deploy/linkerd-controller --as $(whoami)
req id=3:0 proxy=in  src=10.244.0.1:37392 dst=10.244.0.13:9996 tls=not_provided_by_remote :method=GET :authority=10.244.0.13:9996 :path=/ping
...

Cluster admin access

To simply give your user cluster-admin access:

kubectl create clusterrolebinding \
  $(whoami)-cluster-admin \
  --clusterrole=cluster-admin \
  --user=$(whoami)

GKE

Google Kubernetes Engine (GKE) provides access to your Kubernetes cluster via Google Cloud IAM. See the GKE IAM Docs for more information.

Because GCloud provides this additional level of access, there are cases where kubectl auth can-i will report you have Tap access when your RBAC user may not. To validate this, check whether your GCloud user has Tap access:

$ kubectl auth can-i watch pods.tap.linkerd.io --all-namespaces
yes

And then validate whether your RBAC user has Tap access:

$ kubectl auth can-i watch pods.tap.linkerd.io --all-namespaces --as $(gcloud config get-value account)
no - no RBAC policy matched

If the second command reported you do not have access, you may enable access with:

kubectl create clusterrolebinding \
  $(whoami)-tap-admin \
  --clusterrole=linkerd-linkerd-tap-admin \
  --user=$(gcloud config get-value account)

To simply give your user cluster-admin access:

kubectl create clusterrolebinding \
  $(whoami)-cluster-admin \
  --clusterrole=cluster-admin \
  --user=$(gcloud config get-value account)

Linkerd Dashboard tap access

By default, the Linkerd dashboard has the RBAC privileges necessary to tap resources.

To confirm:

$ kubectl auth can-i watch pods.tap.linkerd.io --all-namespaces --as system:serviceaccount:linkerd:linkerd-web
yes

This access is enabled via a linkerd-linkerd-web-admin ClusterRoleBinding:

$ kubectl describe clusterrolebindings/linkerd-linkerd-web-admin
Name:         linkerd-linkerd-web-admin
Labels:       linkerd.io/control-plane-component=web
              linkerd.io/control-plane-ns=linkerd
Annotations:  kubectl.kubernetes.io/last-applied-configuration:
                {"apiVersion":"rbac.authorization.k8s.io/v1","kind":"ClusterRoleBinding","metadata":{"annotations":{},"labels":{"linkerd.io/control-plane-...
Role:
  Kind:  ClusterRole
  Name:  linkerd-linkerd-tap-admin
Subjects:
  Kind            Name         Namespace
  ----            ----         ---------
  ServiceAccount  linkerd-web  linkerd

If you would like to restrict the Linkerd dashboard’s tap access. You may install Linkerd with the --restrict-dashboard-privileges flag:

linkerd install --restrict-dashboard-privileges

This will omit the linkerd-linkerd-web-admin ClusterRoleBinding. If you have already installed Linkerd, you may simply delete the ClusterRoleBinding manually:

kubectl delete clusterrolebindings/linkerd-linkerd-web-admin

To confirm:

$ kubectl auth can-i watch pods.tap.linkerd.io --all-namespaces --as system:serviceaccount:linkerd:linkerd-web
no