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Creating a network policy

Example NetworkPolicy object

The following configuration annotates an example NetworkPolicy object:

kind: NetworkPolicy
apiVersion: networking.k8s.io/v1
metadata:
  name: allow-27107
spec:
  podSelector:
    matchLabels:
      app: mongodb
  ingress:
  - from:
    - podSelector:
        matchLabels:
          app: app
    ports:
    - protocol: TCP
      port: 27017

where:

name

The name of the NetworkPolicy object.

spec.podSelector

A selector that describes the pods to which the policy applies. The policy object can only select pods in the project that defines the NetworkPolicy object.

ingress.from.podSelector

A selector that matches the pods from which the policy object allows ingress traffic. The selector matches pods in the same namespace as the NetworkPolicy.

ingress.ports

A list of one or more destination ports on which to accept traffic.

Creating a network policy using the CLI

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

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 network plugin that supports NetworkPolicy objects, such as the OVN-Kubernetes network plugin or the OpenShift SDN network plugin with mode: NetworkPolicy set. This mode is the default for OpenShift SDN.

  • You installed the OpenShift CLI (oc).

  • You 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

      where:

      <policy_name>

      Specifies the network policy file name.

    2. Define a network policy in the created file. The following example denies ingress traffic from all pods in all namespaces. This is a fundamental policy, blocking all cross-pod networking other than cross-pod traffic allowed by the configuration of other Network Policies.

      kind: NetworkPolicy
apiVersion: networking.k8s.io/v1
spec:
  podSelector: {}
  policyTypes:
  - Ingress
  ingress: []

      The following example configuration allows ingress traffic from all pods in the same namespace:

      kind: NetworkPolicy
apiVersion: networking.k8s.io/v1
metadata:
  name: allow-same-namespace
spec:
  podSelector:
  ingress:
  - from:
    - podSelector: {}
# ...

      The following example allows ingress traffic to one pod from a particular namespace. This policy allows traffic to pods that have the pod-a label from pods running in namespace-y.

      kind: NetworkPolicy
apiVersion: networking.k8s.io/v1
metadata:
  name: allow-traffic-pod
spec:
  podSelector:
   matchLabels:
      pod: pod-a
  policyTypes:
  - Ingress
  ingress:
  - from:
    - namespaceSelector:
        matchLabels:
           kubernetes.io/metadata.name: namespace-y
# ...

      The following example configuration restricts traffic to a service. This policy when applied ensures every pod with both labels app=bookstore and role=api can only be accessed by pods with label app=bookstore. In this example the application could be a REST API server, marked with labels app=bookstore and role=api.

      This example configuration addresses the following use cases:

      • Restricting the traffic to a service to only the other microservices that need to use it.

      • Restricting the connections to a database to only permit the application using it.

        kind: NetworkPolicy
apiVersion: networking.k8s.io/v1
metadata:
  name: api-allow
spec:
  podSelector:
    matchLabels:
      app: bookstore
      role: api
  ingress:
  - from:
      - podSelector:
          matchLabels:
            app: bookstore
# ...

  2. To create the network policy object, enter the following command. Successful output lists the name of the policy object and the created status.

    $ oc apply -f <policy_name>.yaml -n <namespace>

    where:

    <policy_name>

    Specifies the network policy file name.

    <namespace>

    Optional parameter. If you defined the object in a different namespace than the current namespace, the parameter specifices the namespace.

    Successful output lists the name of the policy object and the created status.

    If you log in to the web console with cluster-admin privileges, you have a choice of creating a network policy in any namespace in the cluster directly in YAML or from a form in the web console.

Creating a default deny all network policy

The default deny all network policy blocks all cross-pod networking other than network traffic allowed by the configuration of other deployed network policies and traffic between host-networked pods. This procedure enforces a strong deny policy by applying a deny-by-default policy in the my-project namespace.

Without configuring a NetworkPolicy custom resource (CR) that allows traffic communication, the following policy might cause communication problems across your cluster.
Prerequisites

  • Your cluster uses a network plugin that supports NetworkPolicy objects, such as the OVN-Kubernetes network plugin or the OpenShift SDN network plugin with mode: NetworkPolicy set. This mode is the default for OpenShift SDN.

  • You installed the OpenShift CLI (oc).

  • You 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 the following YAML that defines a deny-by-default policy to deny ingress from all pods in all namespaces. Save the YAML in the deny-by-default.yaml file:

    kind: NetworkPolicy
apiVersion: networking.k8s.io/v1
metadata:
  name: deny-by-default
  namespace: my-project
spec:
  podSelector: {}
  ingress: []

    where:

    namespace

    Specifies the namespace in which to deploy the policy. For example, the my-project namespace.

    podSelector

    If this field is empty, the configuration matches all the pods. Therefore, the policy applies to all pods in the my-project namespace.

    ingress

    Where [] indicates that no ingress rules are specified. This causes incoming traffic to be dropped to all pods.

  2. Apply the policy by entering the following command. Successful output lists the name of the policy object and the created status.

    $ oc apply -f deny-by-default.yaml

Creating a network policy to allow traffic from external clients

With the deny-by-default policy in place you can proceed to configure a policy that allows traffic from external clients to a pod with the label app=web.

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.

Follow this procedure to configure a policy that allows external service from the public Internet directly or by using a Load Balancer to access the pod. Traffic is only allowed to a pod with the label app=web.

Prerequisites

  • Your cluster uses a network plugin that supports NetworkPolicy objects, such as the OVN-Kubernetes network plugin or the OpenShift SDN network plugin with mode: NetworkPolicy set. This mode is the default for OpenShift SDN.

  • You installed the OpenShift CLI (oc).

  • You 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 that allows traffic from the public Internet directly or by using a load balancer to access the pod. Save the YAML in the web-allow-external.yaml file:

    kind: NetworkPolicy
apiVersion: networking.k8s.io/v1
spec:
  policyTypes:
  - Ingress
  podSelector:
    matchLabels:
      app: web
  ingress:
    - {}

  2. Apply the policy by entering the following command. Successful output lists the name of the policy object and the created status.

    $ oc apply -f web-allow-external.yaml

    This policy allows traffic from all resources, including external traffic as illustrated in the following diagram:

Allow traffic from external clients

Creating a network policy allowing traffic to an application from all namespaces

You can configure a policy that allows traffic from all pods in all namespaces to a particular application.

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 network plugin that supports NetworkPolicy objects, such as the OVN-Kubernetes network plugin or the OpenShift SDN network plugin with mode: NetworkPolicy set. This mode is the default for OpenShift SDN.

  • You installed the OpenShift CLI (oc).

  • You 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 that allows traffic from all pods in all namespaces to a particular application. Save the YAML in the web-allow-all-namespaces.yaml file:

    kind: NetworkPolicy
apiVersion: networking.k8s.io/v1
spec:
  podSelector:
    matchLabels:
      app: web
  policyTypes:
  - Ingress
  ingress:
  - from:
    - namespaceSelector: {}

    where:

    app

    Applies the policy only to app:web pods in default namespace.

    namespaceSelector

    Selects all pods in all namespaces.

    By default, if you do not specify a namespaceSelector parameter in the policy object, no namespaces get selected. This means the policy allows traffic only from the namespace where the network policy deployes.

  2. Apply the policy by entering the following command. Successful output lists the name of the policy object and the created status.

    $ oc apply -f web-allow-all-namespaces.yaml
Verification

  1. Start a web service in the default namespace by entering the following command:

    $ oc run web --namespace=default --image=nginx --labels="app=web" --expose --port=80

  2. Run the following command to deploy an alpine image in the secondary namespace and to start a shell:

    $ oc run test-$RANDOM --namespace=secondary --rm -i -t --image=alpine -- sh

  3. Run the following command in the shell and observe that the service allows the request:

    # wget -qO- --timeout=2 http://web.default
    <!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
html { color-scheme: light dark; }
body { width: 35em; margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif; }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

Creating a network policy allowing traffic to an application from a namespace

You can configure a policy that allows traffic to a pod with the label app=web from a particular namespace. This configuration is useful in the following use cases:

  • Restrict traffic to a production database only to namespaces that have production workloads deployed.

  • Enable monitoring tools deployed to a particular namespace to scrape metrics from the current namespace.

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 network plugin that supports NetworkPolicy objects, such as the OVN-Kubernetes network plugin or the OpenShift SDN network plugin with mode: NetworkPolicy set. This mode is the default for OpenShift SDN.

  • You installed the OpenShift CLI (oc).

  • You 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 that allows traffic from all pods in a particular namespaces with a label purpose=production. Save the YAML in the web-allow-prod.yaml file:

    kind: NetworkPolicy
apiVersion: networking.k8s.io/v1
metadata:
  name: web-allow-prod
  namespace: default
spec:
  podSelector:
    matchLabels:
      app: web
  policyTypes:
  - Ingress
  ingress:
  - from:
    - namespaceSelector:
        matchLabels:
          purpose: production

    where:

    app

    Applies the policy only to app:web pods in the default namespace.

    purpose

    Restricts traffic to only pods in namespaces that have the label purpose=production.

  2. Apply the policy by entering the following command. Successful output lists the name of the policy object and the created status.

    $ oc apply -f web-allow-prod.yaml
Verification

  1. Start a web service in the default namespace by entering the following command:

    $ oc run web --namespace=default --image=nginx --labels="app=web" --expose --port=80

  2. Run the following command to create the prod namespace:

    $ oc create namespace prod

  3. Run the following command to label the prod namespace:

    $ oc label namespace/prod purpose=production

  4. Run the following command to create the dev namespace:

    $ oc create namespace dev

  5. Run the following command to label the dev namespace:

    $ oc label namespace/dev purpose=testing

  6. Run the following command to deploy an alpine image in the dev namespace and to start a shell:

    $ oc run test-$RANDOM --namespace=dev --rm -i -t --image=alpine -- sh

  7. Run the following command in the shell and observe the reason for the blocked request. For example, expected output states wget: download timed out.

    # wget -qO- --timeout=2 http://web.default

  8. Run the following command to deploy an alpine image in the prod namespace and start a shell:

    $ oc run test-$RANDOM --namespace=prod --rm -i -t --image=alpine -- sh

  9. Run the following command in the shell and observe that the request is allowed:

    # wget -qO- --timeout=2 http://web.default
    <!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
<style>
html { color-scheme: light dark; }
body { width: 35em; margin: 0 auto;
font-family: Tahoma, Verdana, Arial, sans-serif; }
</style>
</head>
<body>
<h1>Welcome to nginx!</h1>
<p>If you see this page, the nginx web server is successfully installed and
working. Further configuration is required.</p>

<p>For online documentation and support please refer to
<a href="http://nginx.org/">nginx.org</a>.<br/>
Commercial support is available at
<a href="http://nginx.com/">nginx.com</a>.</p>

<p><em>Thank you for using nginx.</em></p>
</body>
</html>

Additional resources