As a cluster administrator, you can define network policies that restrict traffic to Pods in your cluster.

About network policy

In a cluster using a Kubernetes Container Network Interface (CNI) plug-in that supports Kubernetes network policy, network isolation is controlled entirely by NetworkPolicy Custom Resource (CR) objects. In OKD Latest, OpenShift SDN supports using NetworkPolicy in its default network isolation mode.

IPBlock is supported in NetworkPolicy with limitations for OpenShift SDN; it supports IPBlock without except clauses. If you create a policy with an IPBlock section including an except clause, the SDN Pods log generates warnings and the entire IPBlock section of that policy is ignored.

Network policy does not apply to the host network namespace. Pods with host networking enabled are unaffected by NetworkPolicy object rules.

By default, all Pods in a project are accessible from other Pods and network endpoints. To isolate one or more Pods in a project, you can create NetworkPolicy objects in that project to indicate the allowed incoming connections. Project administrators can create and delete NetworkPolicy objects within their own project.

If a Pod is matched by selectors in one or more NetworkPolicy objects, then the Pod will accept only connections that are allowed by at least one of those NetworkPolicy objects. A Pod that is not selected by any NetworkPolicy objects is fully accessible.

The following example NetworkPolicy objects demonstrate supporting different scenarios:

  • Deny all traffic:

    To make a project deny by default, add a NetworkPolicy object that matches all Pods but accepts no traffic:

    kind: NetworkPolicy
    apiVersion: networking.k8s.io/v1
    metadata:
      name: deny-by-default
    spec:
      podSelector:
      ingress: []
  • Only allow connections from the OKD Ingress Controller:

    To make a project allow only connections from the OKD Ingress Controller, add the following NetworkPolicy object:

    apiVersion: networking.k8s.io/v1
    kind: NetworkPolicy
    metadata:
      name: allow-from-openshift-ingress
    spec:
      ingress:
      - from:
        - namespaceSelector:
            matchLabels:
              network.openshift.io/policy-group: ingress
      podSelector: {}
      policyTypes:
      - Ingress

    If the Ingress Controller is configured with endpointPublishingStrategy: HostNetwork, then the Ingress Controller Pod runs on the host network. When running on the host network, the traffic from the Ingress Controller is assigned the netid:0 Virtual Network ID (VNID). The netid for the namespace that is associated with the Ingress Operator is different, so the matchLabel in the allow-from-openshift-ingress network policy does not match traffic from the default Ingress Controller. Because the default namespace is assigned the netid:0 VNID, you can allow traffic from the default Ingress Controller by labeling your default namespace with network.openshift.io/policy-group: ingress.

  • Only accept connections from Pods within a project:

    To make Pods accept connections from other Pods in the same project, but reject all other connections from Pods in other projects, add the following NetworkPolicy object:

    kind: NetworkPolicy
    apiVersion: networking.k8s.io/v1
    metadata:
      name: allow-same-namespace
    spec:
      podSelector:
      ingress:
      - from:
        - podSelector: {}
  • Only allow HTTP and HTTPS traffic based on Pod labels:

    To enable only HTTP and HTTPS access to the Pods with a specific label (role=frontend in following example), add a NetworkPolicy object similar to the following:

    kind: NetworkPolicy
    apiVersion: networking.k8s.io/v1
    metadata:
      name: allow-http-and-https
    spec:
      podSelector:
        matchLabels:
          role: frontend
      ingress:
      - ports:
        - protocol: TCP
          port: 80
        - protocol: TCP
          port: 443
  • Accept connections by using both namespace and Pod selectors:

    To match network traffic by combining namespace and Pod selectors, you can use a NetworkPolicy object similar to the following:

    kind: NetworkPolicy
    apiVersion: networking.k8s.io/v1
    metadata:
      name: allow-pod-and-namespace-both
    spec:
      podSelector:
        matchLabels:
          name: test-pods
      ingress:
        - from:
          - namespaceSelector:
              matchLabels:
                project: project_name
            podSelector:
              matchLabels:
                name: test-pods

NetworkPolicy objects are additive, which means you can combine multiple NetworkPolicy objects together to satisfy complex network requirements.

For example, for the NetworkPolicy objects defined in previous samples, you can define both allow-same-namespace and allow-http-and-https policies within the same project. Thus allowing the Pods with the label role=frontend, to accept any connection allowed by each policy. That is, connections on any port from Pods in the same namespace, and connections on ports 80 and 443 from Pods in any namespace.