Apply Calico policy to Kubernetes node ports

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    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
    • HostEndpoint

    Concepts

    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
    • 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.

    For services that you want to expose to external clients, configure Kubernetes services with type NodePort.

    How to

    In the following example, we create a global network policy to allow cluster ingress traffic (allow-cluster-internal-ingress): for the nodes’ IP addresses (1.2.3.4/16), 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.

    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 .

    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.

    When creating each host endpoint, replace with the IP address on eth0. The expectedIPs field is required so that any selectors within ingress or egress rules can properly match the host endpoint.

    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.

    To make the NodePort accessible only through particular nodes, give the nodes a particular label. For example: