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Chapter 9. Network policy

9.1. About network policy
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As a cluster administrator, you can define network policies that restrict traffic to pods in your cluster.

9.1.1. About network policy
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In a cluster using a Kubernetes Container Network Interface (CNI) plug-in that supports Kubernetes network policy, network isolation is controlled entirely by NetworkPolicy objects. In OpenShift Container Platform 4.5, OpenShift SDN supports using network policy in its default network isolation mode.

Note

When using the OpenShift SDN cluster network provider, the following limitations apply regarding network policies:

  • Egress network policy as specified by the egress field is not supported.
  • IPBlock is supported by network policy, but without support for except clauses. If you create a policy with an IPBlock section that includes an except clause, the SDN pods log warnings and the entire IPBlock section of that policy is ignored.
Warning

Network policy does not apply to the host network namespace. Pods with host networking enabled are unaffected by network policy 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: []
    Copy to Clipboard Toggle word wrap

  • Only allow connections from the OpenShift Container Platform Ingress Controller:

    To make a project allow only connections from the OpenShift Container Platform Ingress Controller, add the following NetworkPolicy object.

    Important

    For the OVN-Kubernetes network provider plug-in, when the Ingress Controller is configured to use the HostNetwork endpoint publishing strategy, there is no supported way to apply network policy so that ingress traffic is allowed and all other traffic is denied. 

    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
    Copy to Clipboard Toggle word wrap

    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. With OpenShift SDN, the default namespace is assigned the netid:0 VNID and 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: {}
    Copy to Clipboard Toggle word wrap

  • 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
    Copy to Clipboard Toggle word wrap

  • 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
    Copy to Clipboard Toggle word wrap

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.

9.1.2. Optimizations for network policy
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Use a network policy to isolate pods that are differentiated from one another by labels within a namespace.

Note

The guidelines for efficient use of network policy rules applies to only the OpenShift SDN cluster network provider.

It is inefficient to apply NetworkPolicy objects to large numbers of individual pods in a single namespace. Pod labels do not exist at the IP address level, so a network policy generates a separate Open vSwitch (OVS) flow rule for every possible link between every pod selected with a podSelector.

For example, if the spec podSelector and the ingress podSelector within a NetworkPolicy object each match 200 pods, then 40,000 (200*200) OVS flow rules are generated. This might slow down a node.

When designing your network policy, refer to the following guidelines:

  • Reduce the number of OVS flow rules by using namespaces to contain groups of pods that need to be isolated.

    NetworkPolicy objects that select a whole namespace, by using the namespaceSelector or an empty podSelector, generate only a single OVS flow rule that matches the VXLAN virtual network ID (VNID) of the namespace.

  • Keep the pods that do not need to be isolated in their original namespace, and move the pods that require isolation into one or more different namespaces.
  • Create additional targeted cross-namespace network policies to allow the specific traffic that you do want to allow from the isolated pods.

9.1.3. Next steps
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9.1.4. Additional resources
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9.2. Creating a network policy
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As a user with the admin role, you can create a network policy for a namespace.

9.2.1. Creating a network policy
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To define granular rules describing ingress or egress network traffic allowed for namespaces in your cluster, you can create a network policy.

Note

If you log in with a user with the cluster-admin role, then you can create a network policy in any namespace in the cluster.

Prerequisites

  • Your cluster uses a cluster network provider that supports NetworkPolicy objects, such as the OpenShift SDN network provider with mode: NetworkPolicy set. This mode is the default for OpenShift SDN.
  • You installed the OpenShift CLI (oc).
  • You are logged in to the cluster with a user with admin privileges.
  • You are working in the namespace that the network policy applies to.

Procedure

  1. Create a policy rule:

    1. Create a <policy_name>.yaml file: 

      $ touch <policy_name>.yaml
      Copy to Clipboard Toggle word wrap

      where:

      <policy_name>
      Specifies the network policy file name.

    2. Define a network policy in the file that you just created, such as in the following examples:

      Deny ingress from all pods in all namespaces

      kind: NetworkPolicy
apiVersion: networking.k8s.io/v1
metadata:
  name: deny-by-default
spec:
  podSelector:
  ingress: []
      Copy to Clipboard Toggle word wrap

      Allow ingress from all pods in the same namespace

      kind: NetworkPolicy
apiVersion: networking.k8s.io/v1
metadata:
  name: allow-same-namespace
spec:
  podSelector:
  ingress:
  - from:
    - podSelector: {}
      Copy to Clipboard Toggle word wrap

  2. To create the network policy object, enter the following command: 

    $ oc apply -f <policy_name>.yaml -n <namespace>
    Copy to Clipboard Toggle word wrap

    where:

    <policy_name>
    Specifies the network policy file name.
    <namespace>
    Optional: Specifies the namespace if the object is defined in a different namespace than the current namespace.

    Example output

    networkpolicy "default-deny" created
    Copy to Clipboard Toggle word wrap

9.2.2. Example NetworkPolicy object
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The following annotates an example NetworkPolicy object: 

kind: NetworkPolicy
apiVersion: networking.k8s.io/v1
metadata:
  name: allow-27107
1 

spec:
  podSelector:
2 

    matchLabels:
      app: mongodb
  ingress:
  - from:
    - podSelector:
3 

        matchLabels:
          app: app
    ports:
4 

    - protocol: TCP
      port: 27017
Copy to Clipboard Toggle word wrap
1
The name of the NetworkPolicy object.
2
A selector describing the pods the policy applies to. The policy object can only select pods in the project that the NetworkPolicy object is defined.
3
A selector matching the pods that the policy object allows ingress traffic from. The selector will match pods in any project.
4
A list of one or more destination ports to accept traffic on.

9.3. Viewing a network policy
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As a user with the admin role, you can view a network policy for a namespace.

9.3.1. Viewing network policies
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You can examine the network policies in a namespace.

Note

If you log in with a user with the cluster-admin role, then you can view any network policy in the cluster.

Prerequisites

  • You installed the OpenShift CLI (oc).
  • You are logged in to the cluster with a user with admin privileges.
  • You are working in the namespace where the network policy exists.

Procedure

  • List network policies in a namespace:

    • To view NetworkPolicy objects defined in a namespace, enter the following command: 

      $ oc get networkpolicy
      Copy to Clipboard Toggle word wrap

    • Optional: To examine a specific network policy, enter the following command: 

      $ oc describe networkpolicy <policy_name> -n <namespace>
      Copy to Clipboard Toggle word wrap

      where:

      <policy_name>
      Specifies the name of the network policy to inspect.
      <namespace>
      Optional: Specifies the namespace if the object is defined in a different namespace than the current namespace.

      For example: 

      $ oc describe networkpolicy allow-same-namespace
      Copy to Clipboard Toggle word wrap

      Output for oc describe command

      Name:         allow-same-namespace
Namespace:    ns1
Created on:   2021-05-24 22:28:56 -0400 EDT
Labels:       <none>
Annotations:  <none>
Spec:
  PodSelector:     <none> (Allowing the specific traffic to all pods in this namespace)
  Allowing ingress traffic:
    To Port: <any> (traffic allowed to all ports)
    From:
      PodSelector: <none>
  Not affecting egress traffic
  Policy Types: Ingress
      Copy to Clipboard Toggle word wrap

9.3.2. Example NetworkPolicy object
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The following annotates an example NetworkPolicy object: 

kind: NetworkPolicy
apiVersion: networking.k8s.io/v1
metadata:
  name: allow-27107
1 

spec:
  podSelector:
2 

    matchLabels:
      app: mongodb
  ingress:
  - from:
    - podSelector:
3 

        matchLabels:
          app: app
    ports:
4 

    - protocol: TCP
      port: 27017
Copy to Clipboard Toggle word wrap
1
The name of the NetworkPolicy object.
2
A selector describing the pods the policy applies to. The policy object can only select pods in the project that the NetworkPolicy object is defined.
3
A selector matching the pods that the policy object allows ingress traffic from. The selector will match pods in any project.
4
A list of one or more destination ports to accept traffic on.

9.4. Editing a network policy
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As a user with the admin role, you can edit an existing network policy for a namespace.

9.4.1. Editing a network policy
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You can edit a network policy in a namespace.

Note

If you log in with a user with the cluster-admin role, then you can edit a network policy in any namespace in the cluster.

Prerequisites

  • Your cluster uses a cluster network provider that supports NetworkPolicy objects, such as the OpenShift SDN network provider with mode: NetworkPolicy set. This mode is the default for OpenShift SDN.
  • You installed the OpenShift CLI (oc).
  • You are logged in to the cluster with a user with admin privileges.
  • You are working in the namespace where the network policy exists.

Procedure

  1. Optional: To list the network policy objects in a namespace, enter the following command: 

    $ oc get networkpolicy -n <namespace>
    Copy to Clipboard Toggle word wrap

    where:

    <namespace>
    Optional: Specifies the namespace if the object is defined in a different namespace than the current namespace.

  2. Edit the NetworkPolicy object.

    • If you saved the network policy definition in a file, edit the file and make any necessary changes, and then enter the following command. 

      $ oc apply -n <namespace> -f <policy_file>.yaml
      Copy to Clipboard Toggle word wrap

      where:

      <namespace>
      Optional: Specifies the namespace if the object is defined in a different namespace than the current namespace.
      <policy_file>
      Specifies the name of the file containing the network policy.

    • If you need to update the NetworkPolicy object directly, enter the following command: 

      $ oc edit networkpolicy <policy_name> -n <namespace>
      Copy to Clipboard Toggle word wrap

      where:

      <policy_name>
      Specifies the name of the network policy.
      <namespace>
      Optional: Specifies the namespace if the object is defined in a different namespace than the current namespace.

  3. Confirm that the NetworkPolicy object is updated. 

    $ oc describe networkpolicy <policy_name> -n <namespace>
    Copy to Clipboard Toggle word wrap

    where:

    <policy_name>
    Specifies the name of the network policy.
    <namespace>
    Optional: Specifies the namespace if the object is defined in a different namespace than the current namespace.

9.4.2. Example NetworkPolicy object
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The following annotates an example NetworkPolicy object: 

kind: NetworkPolicy
apiVersion: networking.k8s.io/v1
metadata:
  name: allow-27107
1 

spec:
  podSelector:
2 

    matchLabels:
      app: mongodb
  ingress:
  - from:
    - podSelector:
3 

        matchLabels:
          app: app
    ports:
4 

    - protocol: TCP
      port: 27017
Copy to Clipboard Toggle word wrap
1
The name of the NetworkPolicy object.
2
A selector describing the pods the policy applies to. The policy object can only select pods in the project that the NetworkPolicy object is defined.
3
A selector matching the pods that the policy object allows ingress traffic from. The selector will match pods in any project.
4
A list of one or more destination ports to accept traffic on.

9.4.3. Additional resources
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9.5. Deleting a network policy
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As a user with the admin role, you can delete a network policy from a namespace.

9.5.1. Deleting a network policy
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You can delete a network policy in a namespace.

Note

If you log in with a user with the cluster-admin role, then you can delete any network policy in the cluster.

Prerequisites

  • Your cluster uses a cluster network provider that supports NetworkPolicy objects, such as the OpenShift SDN network provider with mode: NetworkPolicy set. This mode is the default for OpenShift SDN.
  • You installed the OpenShift CLI (oc).
  • You are logged in to the cluster with a user with admin privileges.
  • You are working in the namespace where the network policy exists.

Procedure

  • To delete a NetworkPolicy object, enter the following command: 

    $ oc delete networkpolicy <policy_name> -n <namespace>
    Copy to Clipboard Toggle word wrap

    where:

    <policy_name>
    Specifies the name of the network policy.
    <namespace>
    Optional: Specifies the namespace if the object is defined in a different namespace than the current namespace.

    Example output

    networkpolicy.networking.k8s.io/allow-same-namespace deleted
    Copy to Clipboard Toggle word wrap

9.6. Defining a default network policy for projects
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As a cluster administrator, you can modify the new project template to automatically include network policies when you create a new project. If you do not yet have a customized template for new projects, you must first create one.

9.6.1. Modifying the template for new projects
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As a cluster administrator, you can modify the default project template so that new projects are created using your custom requirements.

To create your own custom project template:

Procedure

  1. Log in as a user with cluster-admin privileges.

  2. Generate the default project template: 

    $ oc adm create-bootstrap-project-template -o yaml > template.yaml
    Copy to Clipboard Toggle word wrap
  3. Use a text editor to modify the generated template.yaml file by adding objects or modifying existing objects.

  4. The project template must be created in the openshift-config namespace. Load your modified template: 

    $ oc create -f template.yaml -n openshift-config
    Copy to Clipboard Toggle word wrap

  5. Edit the project configuration resource using the web console or CLI.

    • Using the web console:

      1. Navigate to the Administration Cluster Settings page.
      2. Click Global Configuration to view all configuration resources.
      3. Find the entry for Project and click Edit YAML.

    • Using the CLI:

      1. Edit the project.config.openshift.io/cluster resource: 

        $ oc edit project.config.openshift.io/cluster
        Copy to Clipboard Toggle word wrap

  6. Update the spec section to include the projectRequestTemplate and name parameters, and set the name of your uploaded project template. The default name is project-request.

    Project configuration resource with custom project template

    apiVersion: config.openshift.io/v1
kind: Project
metadata:
  ...
spec:
  projectRequestTemplate:
    name: <template_name>
    Copy to Clipboard Toggle word wrap

  7. After you save your changes, create a new project to verify that your changes were successfully applied.

9.6.2. Adding network policies to the new project template
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As a cluster administrator, you can add network policies to the default template for new projects. OpenShift Container Platform will automatically create all the NetworkPolicy objects specified in the template in the project.

Prerequisites

  • Your cluster uses a default CNI network provider that supports NetworkPolicy objects, such as the OpenShift SDN network provider with mode: NetworkPolicy set. This mode is the default for OpenShift SDN.
  • You installed the OpenShift CLI (oc).
  • You must log in to the cluster with a user with cluster-admin privileges.
  • You must have created a custom default project template for new projects.

Procedure

  1. Edit the default template for a new project by running the following command: 

    $ oc edit template <project_template> -n openshift-config
    Copy to Clipboard Toggle word wrap

    Replace <project_template> with the name of the default template that you configured for your cluster. The default template name is project-request.

  2. In the template, add each NetworkPolicy object as an element to the objects parameter. The objects parameter accepts a collection of one or more objects.

    In the following example, the objects parameter collection includes several NetworkPolicy objects: 

    objects:
- apiVersion: networking.k8s.io/v1
  kind: NetworkPolicy
  metadata:
    name: allow-from-same-namespace
  spec:
    podSelector:
    ingress:
    - from:
      - podSelector: {}
- 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
...
    Copy to Clipboard Toggle word wrap

  3. Optional: Create a new project to confirm that your network policy objects are created successfully by running the following commands:

    1. Create a new project: 

      $ oc new-project <project>
      1
      Copy to Clipboard Toggle word wrap
      1
      Replace <project> with the name for the project you are creating.

    2. Confirm that the network policy objects in the new project template exist in the new project: 

      $ oc get networkpolicy
NAME                           POD-SELECTOR   AGE
allow-from-openshift-ingress   <none>         7s
allow-from-same-namespace      <none>         7s
      Copy to Clipboard Toggle word wrap

9.7. Configuring multitenant isolation with network policy
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As a cluster administrator, you can configure your network policies to provide multitenant network isolation.

Note

If you are using the OpenShift SDN cluster network provider, configuring network policies as described in this section provides network isolation similar to multitenant mode but with network policy mode set.

9.7.1. Configuring multitenant isolation by using network policy
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You can configure your project to isolate it from pods and services in other project namespaces.

Prerequisites

  • Your cluster uses a cluster network provider that supports NetworkPolicy objects, such as the OpenShift SDN network provider with mode: NetworkPolicy set. This mode is the default for OpenShift SDN.
  • You installed the OpenShift CLI (oc).
  • You are logged in to the cluster with a user with admin privileges.

Procedure

  1. Create the following NetworkPolicy objects:

    1. A policy named allow-from-openshift-ingress.

      Important

      For the OVN-Kubernetes network provider plug-in, when the Ingress Controller is configured to use the HostNetwork endpoint publishing strategy, there is no supported way to apply network policy so that ingress traffic is allowed and all other traffic is denied. 

      $ cat << EOF| oc create -f -
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
EOF
      Copy to Clipboard Toggle word wrap

    2. A policy named allow-from-openshift-monitoring: 

      $ cat << EOF| oc create -f -
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-from-openshift-monitoring
spec:
  ingress:
  - from:
    - namespaceSelector:
        matchLabels:
          network.openshift.io/policy-group: monitoring
  podSelector: {}
  policyTypes:
  - Ingress
EOF
      Copy to Clipboard Toggle word wrap

    3. A policy named allow-same-namespace: 

      $ cat << EOF| oc create -f -
kind: NetworkPolicy
apiVersion: networking.k8s.io/v1
metadata:
  name: allow-same-namespace
spec:
  podSelector:
  ingress:
  - from:
    - podSelector: {}
EOF
      Copy to Clipboard Toggle word wrap

  2. If the default Ingress Controller configuration has the spec.endpointPublishingStrategy: HostNetwork value set, you must apply a label to the default OpenShift Container Platform namespace to allow network traffic between the Ingress Controller and the project:

    1. Determine if your default Ingress Controller uses the HostNetwork endpoint publishing strategy: 

      $ oc get --namespace openshift-ingress-operator ingresscontrollers/default \
  --output jsonpath='{.status.endpointPublishingStrategy.type}'
      Copy to Clipboard Toggle word wrap

    2. If the previous command reports the endpoint publishing strategy as HostNetwork, set a label on the default namespace: 

      $ oc label namespace default 'network.openshift.io/policy-group=ingress'
      Copy to Clipboard Toggle word wrap

  3. Confirm that the NetworkPolicy object exists in your current project by running the following command: 

    $ oc get networkpolicy <policy-name> -o yaml
    Copy to Clipboard Toggle word wrap

    In the following example, the allow-from-openshift-ingress NetworkPolicy object is displayed: 

    $ oc get -n project1 networkpolicy allow-from-openshift-ingress -o yaml
    Copy to Clipboard Toggle word wrap

    Example output

    apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-from-openshift-ingress
  namespace: project1
spec:
  ingress:
  - from:
    - namespaceSelector:
        matchLabels:
          network.openshift.io/policy-group: ingress
  podSelector: {}
  policyTypes:
  - Ingress
    Copy to Clipboard Toggle word wrap

9.7.2. Next steps
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9.7.3. Additional resources
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