Apply policy to Kubernetes node ports
Restrict access to node ports to specific external clients.
Exposing services to external clients using node ports is a standard Kubernetes feature. However, if you want to restrict access to node ports to specific external clients, you need to use Calico global network policy.
This how-to guide uses the following Calico features:
- GlobalNetworkPolicy with a preDNAT field
Network policy with preDNAT field
In a Kubernetes cluster, kube-proxy will DNAT a request to the node’s port and IP address to one of the pods that backs the service. For Calico global network policy to both allow normal ingress cluster traffic and deny other general ingress traffic, it must take effect before DNAT. To do this, you simply add a preDNAT field to a Calico global network policy. The preDNAT field:
- Applies before DNAT
- Applies only to ingress rules
- Enforces all ingress traffic through a host endpoint, regardless of destination
The destination can be a locally hosted pod, a pod on another node, or a process running on the host.
Before you begin…
For services that you want to expose to external clients, configure Kubernetes services with type NodePort.
To securely expose a Kubernetes service to external clients, you must implement all of the following steps.
- Allow cluster ingress traffic, but deny general ingress traffic
- Allow local host egress traffic
- Create host endpoints with appropriate network policy
- Allow ingress traffic to specific node ports
Allow cluster ingress traffic but deny general ingress traffic
In the following example, we create a global network policy to allow cluster ingress traffic (allow-cluster-internal-ingress): for the nodes’ IP addresses (18.104.22.168/16), and for pod IP addresses assigned by Kubernetes (100.100.100.0/16). By adding a preDNAT field, Calico global network policy is applied before regular DNAT on the Kubernetes cluster.
In this example, we use the selector: has(kubernetes-host) – so the policy is applicable to any endpoint with a kubernetes-host label (but you can easily specify particular nodes).
Finally, when you specify a preDNAT field, you must also add the applyOnForward: true field.
apiVersion: projectcalico.org/v3 kind: GlobalNetworkPolicy metadata: name: allow-cluster-internal-ingress-only spec: order: 20 preDNAT: true applyOnForward: true ingress: - action: Allow source: nets: [22.214.171.124/16, 100.100.100.0/16] - action: Deny selector: has(kubernetes-host)
Allow local host egress traffic
We also need a global network policy to allow egress traffic through each node’s external interface. Otherwise, when we define host endpoints for those interfaces, no egress traffic will be allowed from local processes (except for traffic that is allowed by the Failsafe rules.
apiVersion: projectcalico.org/v3 kind: GlobalNetworkPolicy metadata: name: allow-outbound-external spec: order: 10 egress: - action: Allow selector: has(kubernetes-host)
Create host endpoints with appropriate network policy
In this example, we assume that you have already defined Calico host endpoints with network policy that is appropriate for the cluster. (For example, you wouldn’t want a host endpoint with a “default deny all traffic to/from this host” network policy because that is counter to the goal of allowing/denying specific traffic.) For help, see host endpoints.
All of our previously-defined global network policies have a selector that makes them applicable to any endpoint with a kubernetes-host label; so we will include that label in our definitions. For example, for eth0 on node1.
apiVersion: projectcalico.org/v3 kind: HostEndpoint metadata: name: node1-eth0 labels: kubernetes-host: ingress spec: interfaceName: eth0 node: node1
Allow ingress traffic to specific node ports
Now we can allow external access to the node ports by creating a global network policy with the preDNAT field. In this example, ingress traffic is allowed for any host endpoint with port: 31852.
apiVersion: projectcalico.org/v3 kind: GlobalNetworkPolicy metadata: name: allow-nodeport spec: preDNAT: true applyOnForward: true order: 10 ingress: - action: Allow protocol: TCP destination: selector: has(kubernetes-host) ports:  selector: has(kubernetes-host)
To make the NodePort accessible only through particular nodes, give the nodes a particular label. For example:
Then, use nodeport-external-ingress: true as the selector of the allow-nodeport policy, instead of has(kubernetes-host).