Creating a network policy

Creating a network policy
Example NetworkPolicy object

As a user with the admin role, you can create a network policy for a namespace.

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 cluster network provider that supports NetworkPolicy objects, such as the OVN-Kubernetes network provider or 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

Create a policy rule:

Create a <policy_name>.yaml file:
```
$ touch <policy_name>.yaml
```
where:

<policy_name>

Specifies the network policy file name.

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: []

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: {}

To create the network policy object, enter the following command:
```
$ oc apply -f <policy_name>.yaml -n <namespace>
```
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
```

Example NetworkPolicy object

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

1	The name of the NetworkPolicy object.
2	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.
3	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.
4	A list of one or more destination ports on which to accept traffic.