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© 2024

Access the Kubernetes control plane using an API server proxy

You can use the Tailscale Kubernetes operator to expose and access the Kubernetes control plane (kube-apiserver) over Tailscale.

The Tailscale API server proxy can run in one of two modes:

  • Auth mode: In auth mode, requests from the tailnet proxied over to the Kubernetes API server are additionally impersonated using the sender's tailnet identity. Kubernetes RBAC can then be used to configure granular API server permissions for individual tailnet identities or groups.

  • Noauth mode: In noauth mode, requests from the tailnet will be proxied over to the Kubernetes API server but not authenticated. This mechanism can be combined with another authentication/authorization mechanism, such as an authenticating proxy provided by an external IDP or a cloud provider.

Prerequisites

  • Set up the Kubernetes Operator.

  • Enable HTTPS for your tailnet.

  • The API server proxy runs as part of the same process as the Tailscale Kubernetes operator and is reached using the same tailnet device. It is exposed on port 443. Ensure that your ACLs allow all devices and users who want to access the API server using the proxy have access to the Tailscale Kubernetes operator. For example, to allow all tailnet devices tagged with tag:k8s-readers access to the proxy, create an ACL rule like this:

    "acls": [{
	"action": "accept",
	"src": ["tag:k8s-readers"],
	"dst": ["tag:k8s-operator:443"]
}]

    Access to the proxy over the tailnet does not grant tailnet users any default permissions to access Kubernetes API server resources. Tailnet users will only be able to access API server resources that they have been explicitly authorized to access by Kubernetes RBAC.

Configuring the API server proxy in auth mode

Installation

Helm

If you are installing Tailscale Kubernetes operator with Helm, you can install the proxy in auth mode by passing --set-string apiServerProxyConfig.mode=true flag to the install command:

helm upgrade \
  --install \
  tailscale-operator \
  tailscale/tailscale-operator \
  --namespace=tailscale \
  --create-namespace \
  --set-string oauth.clientId=<OAauthClientId> \
  --set-string oauth.clientSecret=<OAuthClientSecret> \
  --set-string apiServerProxyConfig.mode="true" \
  --wait

Static manifests with kubectl

If you are installing Tailscale Kubernetes operator using static manifests:

  1. Set the environment variable API_SERVER_PROXY=true in the Tailscale Kubernetes operator deployment manifest.

    name: APISERVER_PROXY
value: "true"

  2. Download and apply RBAC for the API server proxy from the tailscale/tailscale repo.

Configuring authentication and authorization

API server proxy in auth mode impersonates requests from the tailnet to the Kubernetes API server. You can then use Kubernetes RBAC to control what API server resources tailnet identities can access.

The impersonation is applied as follows:

  • If the user who sends a request to the Kube API server using the proxy is in a tailnet user group for which API server proxy grants have been configured for that proxy instance, the request will be impersonated as a Kubernetes group specified in the grant. It will also be impersonated as a Kubernetes user whose name matches the tailnet user's name.
  • If grants are not used and the node from which the request is sent is tagged, the request will be impersonated as if from a Kubernetes group whose name matches the tag.
  • If grants are not used and the node from which the request is sent is not tagged, the request will be impersonated as a Kubernetes user whose name matches the sender's tailnet username.

Impersonating Kubernetes groups with grants

You can use grants to configure the Kubernetes API server resources Tailscale user groups can access.

For example, to give a tailnet user group group:prod cluster admin access and give the tailnet user group group:k8s-readers read permission for most Kubernetes resources:

  1. Update your grants:

      {
    "grants": [{
      "src": ["group:prod"],
      "dst": ["tag:k8s-operator"],
      "app": {
        "tailscale.com/cap/kubernetes": [{
          "impersonate": {
            "groups": ["system:masters"],
          },
        }],
      },
    }{
      "src": ["group:k8s-readers"],
      "dst": ["tag:k8s-operator"],
      "app": {
        "tailscale.com/cap/kubernetes": [{
          "impersonate": {
            "groups": ["tailnet-readers"],
          },
        }],
      },
    }]
  }
    • grants.src is the Tailscale user group the grant applies to.
    • grants.dst must be the tag of the Tailscale Kubernetes operator.
    • system:masters is a Kubernetes group with default RBAC bindings in all clusters. Kubernetes creates a default ClusterRole cluster-admin that allows all actions against all Kubernetes API server resources and a ClusterRoleBinding cluster-admin that binds the cluster-admin ClusterRole to system:masters group.
    • tailnet-readers is a Kubernetes group that you will bind the default Kubernetes view ClusterRole to in a following step. (Note that Kubernetes group names do not refer to existing identities in Kubernetes- they do not need to be pre-created to start using them in (Cluster)RoleBindings).

  2. Bind tailnet-readers to the view ClusterRole:

    kubectl create clusterrolebinding tailnet-readers-view --group=tailnet-readers --clusterrole=view

Impersonating Kubernetes groups with tagged tailnet nodes

If the request is sent from a tagged device, it will be impersonated as a Kubernetes group whose name matches the tag. For example, a request from a tailnet device tagged with tag:k8s-readers will be authenticated by the API server as from a Kubernetes group tag:k8s-readers.

You can create Kubernetes (Cluster)Roles and (Cluster)RoleBindings to configure the permissions the group should have or bind an existing (Cluster)Role to the group.

For example, to grant devices tagged with tag:k8s-readers read-only access to most Kubernetes resources, you can bind Kubernetes group tag:k8s-users to the default Kubernetes view ClusterRole:

kubectl create clusterrolebinding tailnet-readers --group="tag:k8s-readers" --clusterrole=view

Impersonating Kubernetes users

If the request is not sent from a tagged device, it will be impersonated as a Kubernetes user named the same as the sender's tailnet user.

You can then create Kubernetes (Cluster)Roles and (Cluster)RoleBindings to configure the permissions the user should have or bind an existing (Cluster)Role to the user.

For example, to allow the tailnet user alice@tailscale.com read-only access to most Kubernetes resources, bind Kubernetes user alice@tailscale.com to the default Kubernetes view ClusterRole like so:

kubectl create clusterrolebinding alice-view --user="alice@tailscale.com"  --clusterrole=view

Configuring kubeconfig

You can run the following CLI command to configure your kubeconfig for authentication with kubectl using the Tailscale Kubernetes API server proxy: tailscale configure kubeconfig <operator-hostname>. By default, the hostname for the operator node is tailscale-operator.

Configuring API server proxy in noauth mode

The noauth mode of the API server proxy is useful if you want to use Tailscale to provide access to the Kubernetes API server over the tailnet, but want to keep using your existing authentication and authorization mechanism.

Installation

Helm

If you are installing Tailscale Kubernetes operator with Helm, you can install the proxy in auth mode by passing --set-string apiServerProxyConfig.mode=noauth flag to the install command:

helm upgrade \
  --install \
  tailscale-operator \
  tailscale/tailscale-operator \
  --namespace=tailscale \
  --create-namespace \
  --set-string oauth.clientId=<OAauth client ID> \
  --set-string oauth.clientSecret=<OAuth client secret> \
  --set-string apiServerProxyConfig.mode="noauth" \
  --wait

Static manifests with kubectl

If you are installing Tailscale Kubernetes operator using static manifests:

  1. Set the environment variable API_SERVER_PROXY=noauth in the Tailscale Kubernetes operator deployment manifest.

    name: APISERVER_PROXY
value: "noauth"

Authentication and authorization

When run in noauth mode, the API server proxy exposes the Kubernetes API server to the tailnet but does not provide authentication. You can use the proxy endpoint (<TailscaleOperatorHostname>:443) instead of the Kubernetes API server address and set up authentication and authorization over that using any other mechanism (such as another authenticating proxy provided by your managed Kubernetes provider or IDP or similar).

Customization

Learn how to customize the operator and resources it manages.

Troubleshooting

Learn how to troubleshoot the operator and resources it manages.

Limitations

  • The API server proxy runs inside the cluster. If your cluster is non-functional or unable to schedule pods, you might lose access to the API server proxy and potentially your cluster.
  • The API server proxy requires TLS certificates. Currently, the certificates are provisioned automatically by the proxy on the first API call, meaning the first call might be slow or even time out.