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OVN-Kubernetes network policy - OVN-Kubernetes network plugin | Networking | OKD 4.15
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OVN-Kubernetes network policy

The AdminNetworkPolicy resource is a Technology Preview feature only. Technology Preview features are not supported with Red Hat production service level agreements (SLAs) and might not be functionally complete. Red Hat does not recommend using them in production. These features provide early access to upcoming product features, enabling customers to test functionality and provide feedback during the development process.

For more information about the support scope of Red Hat Technology Preview features, see Technology Preview Features Support Scope.

Kubernetes offers two features that users can use to enforce network security. One feature that allows users to enforce network policy is the NetworkPolicy API that is designed mainly for application developers and namespace tenants to protect their namespaces by creating namespace-scoped policies. For more information, see About network policy.

The second feature is AdminNetworkPolicy which is comprised of two API: the AdminNetworkPolicy (ANP) API and the BaselineAdminNetworkPolicy (BANP) API. ANP and BANP are designed for cluster and network administrators to protect their entire cluster by creating cluster-scoped policies. Cluster administrators can use ANPs to enforce non-overridable policies that take precedence over NetworkPolicy objects. Administrators can use BANP to setup and enforce optional cluster-scoped network policy rules that are overridable by users using NetworkPolicy objects if need be. When used together ANP and BANP can create multi-tenancy policy that administrators can use to secure their cluster.

OVN-Kubernetes CNI in OKD implements these network policies using Access Control List (ACLs) Tiers to evaluate and apply them. ACLs are evaluated in descending order from Tier 1 to Tier 3.

Tier 1 evaluates AdminNetworkPolicy (ANP) objects. Tier 2 evaluates NetworkPolicy objects. Tier 3 evaluates BaselineAdminNetworkPolicy (BANP) objects.

OVN-Kubernetes Access Control List
Figure 1. OVK-Kubernetes Access Control List (ACL)

If traffic matches an ANP rule, the rules in that ANP will be evaluated first. If the match is an ANP allow or deny rule, any existing NetworkPolicies and BaselineAdminNetworkPolicy (BANP) in the cluster will be intentionally skipped from evaluation. If the match is an ANP pass rule, then evaluation moves from tier 1 of the ACLs to tier 2 where the NetworkPolicy policy is evaluated.

AdminNetworkPolicy

An AdminNetworkPolicy (ANP) is a cluster-scoped custom resource definition (CRD). As a OKD administrator, you can use ANP to secure your network by creating network policies before creating namespaces. Additionally, you can create network policies on a cluster-scoped level that is non-overridable by NetworkPolicy objects.

The key difference between AdminNetworkPolicy and NetworkPolicy objects are that the former is for administrators and is cluster scoped while the latter is for tenant owners and is namespace scoped.

An ANP allows administrators to specify the following:

  • A priority value that determines the order of its evaluation. The lower the value the higher the precedence.

  • A subject that consists of a set of namespaces or namespace..

  • A list of ingress rules to be applied for all ingress traffic towards the subject.

  • A list of egress rules to be applied for all egress traffic from the subject.

The AdminNetworkPolicy resource is a TechnologyPreviewNoUpgrade feature that can be enabled on test clusters that are not in production. For more information on feature gates and TechnologyPreviewNoUpgrade features, see "Enabling features using feature gates" in the "Additional resources" of this section.

AdminNetworkPolicy example

Example YAML file for an ANP 
apiVersion: policy.networking.k8s.io/v1alpha1
kind: AdminNetworkPolicy
metadata:
  name: sample-anp-deny-pass-rules (1)
spec:
  priority: 50 (2)
  subject:
    namespaces:
      matchLabels:
          kubernetes.io/metadata.name: example.name (3)
  ingress: (4)
  - name: "deny-all-ingress-tenant-1" (5)
    action: "Deny"
    from:
    - pods:
        namespaces: (6)
          namespaceSelector:
            matchLabels:
              custom-anp: tenant-1
        podSelector:
          matchLabels:
            custom-anp: tenant-1 (7)
  egress:(8)
  - name: "pass-all-egress-to-tenant-1"
    action: "Pass"
    to:
    - pods:
        namespaces:
          namespaceSelector:
            matchLabels:
              custom-anp: tenant-1
        podSelector:
          matchLabels:
            custom-anp: tenant-1
1 Specify a name for your ANP.
2 The spec.priority field supports a maximum of 100 ANP in the values of 0-99 in a cluster. The lower the value the higher the precedence. Creating AdminNetworkPolicy with the same priority creates a nondeterministic outcome.
3 Specify the namespace to apply the ANP resource.
4 ANP have both ingress and egress rules. ANP rules for spec.ingress field accepts values of Pass, Deny, and Allow for the action field.
5 Specify a name for the ingress.name.
6 Specify the namespaces to select the pods from to apply the ANP resource.
7 Specify podSelector.matchLabels name of the pods to apply the ANP resource.
8 ANP have both ingress and egress rules. ANP rules for spec.egress field accepts values of Pass, Deny, and Allow for the action field.
Additional resources

AdminNetworkPolicy actions for rules

As an administrator, you can set Allow, Deny, or Pass as the action field for your AdminNetworkPolicy rules. Because OVN-Kubernetes uses a tiered ACLs to evaluate network traffic rules, ANP allow you to set very strong policy rules that can only be changed by an administrator modifying them, deleting the rule, or overriding them by setting a higher priority rule.

AdminNetworkPolicy Allow example

The following ANP that is defined at priority 9 ensures all ingress traffic is allowed from the monitoring namespace towards any tenant (all other namespaces) in the cluster.

Example YAML file for a strong Allow ANP 
apiVersion: policy.networking.k8s.io/v1alpha1
kind: AdminNetworkPolicy
metadata:
  name: allow-monitoring
spec:
  priority: 9
  subject:
    namespaces: {}
  ingress:
  - name: "allow-ingress-from-monitoring"
    action: "Allow"
    from:
    - namespaces:
        namespaceSelector:
          matchLabels:
            kubernetes.io/metadata.name: monitoring
# ...

This is an example of a strong Allow ANP because it is non-overridable by all the parties involved. No tenants can block themselves from being monitored using NetworkPolicy objects and the monitoring tenant also has no say in what it can or cannot monitor.

AdminNetworkPolicy Deny example

The following ANP that is defined at priority 5 ensures all ingress traffic from the monitoring namespace is blocked towards restricted tenants (namespaces that have labels security: restricted).

Example YAML file for a strong Deny ANP 
apiVersion: policy.networking.k8s.io/v1alpha1
kind: AdminNetworkPolicy
metadata:
  name: block-monitoring
spec:
  priority: 5
  subject:
    namespaces:
      matchLabels:
        security: restricted
  ingress:
  - name: "deny-ingress-from-monitoring"
    action: "Deny"
    from:
    - namespaces:
        namespaceSelector:
          matchLabels:
            kubernetes.io/metadata.name: monitoring
# ...

This is a strong Deny ANP that is non-overridable by all the parties involved. The restricted tenant owners cannot authorize themselves to allow monitoring traffic, and the infrastructure’s monitoring service cannot scrape anything from these sensitive namespaces.

When combined with the strong Allow example, the block-monitoring ANP has a lower priority value giving it higher precedence, which ensures restricted tenants are never monitored.

AdminNetworkPolicy Pass example

TThe following ANP that is defined at priority 7 ensures all ingress traffic from the monitoring namespace towards internal infrastructure tenants (namespaces that have labels security: internal) are passed on to tier 2 of the ACLs and evaluated by the namespaces’ NetworkPolicy objects.

Example YAML file for a strong Pass ANP 
apiVersion: policy.networking.k8s.io/v1alpha1
kind: AdminNetworkPolicy
metadata:
  name: pass-monitoring
spec:
  priority: 7
  subject:
    namespaces:
      matchLabels:
        security: internal
  ingress:
  - name: "pass-ingress-from-monitoring"
    action: "Pass"
    from:
    - namespaces:
        namespaceSelector:
          matchLabels:
            kubernetes.io/metadata.name: monitoring
# ...

This example is a strong Pass action ANP because it delegates the decision to NetworkPolicy objects defined by tenant owners. This pass-monitoring ANP allows all tenant owners grouped at security level internal to choose if their metrics should be scraped by the infrastructures' monitoring service using namespace scoped NetworkPolicy objects.

BaselineAdminNetworkPolicy

BaselineAdminNetworkPolicy (BANP) is a cluster-scoped custom resource definition (CRD). As a OKD administrator, you can use BANP to setup and enforce optional baseline network policy rules that are overridable by users using NetworkPolicy objects if need be. Rule actions for BANP are allow or deny.

The BaselineAdminNetworkPolicy resource is a cluster singleton object that can be used as a guardrail policy incase a passed traffic policy does not match any NetworkPolicy objects in the cluster. A BANP can also be used as a default security model that provides guardrails that intra-cluster traffic is blocked by default and a user will need to use NetworkPolicy objects to allow known traffic. You must use default as the name when creating a BANP resource.

A BANP allows administrators to specify:

  • A subject that consists of a set of namespaces or namespace.

  • A list of ingress rules to be applied for all ingress traffic towards the subject.

  • A list of egress rules to be applied for all egress traffic from the subject.

BaselineAdminNetworkPolicy is a TechnologyPreviewNoUpgrade feature that can be enabled on test clusters that are not in production.

BaselineAdminNetworkPolicy example

Example YAML file for BANP 
apiVersion: policy.networking.k8s.io/v1alpha1
kind: BaselineAdminNetworkPolicy
metadata:
  name: default (1)
spec:
  subject:
    namespaces:
      matchLabels:
          kubernetes.io/metadata.name: example.name (2)
  ingress: (3)
  - name: "deny-all-ingress-from-tenant-1" (4)
    action: "Deny"
    from:
    - pods:
        namespaces:
          namespaceSelector:
            matchLabels:
              custom-banp: tenant-1 (5)
        podSelector:
          matchLabels:
            custom-banp: tenant-1 (6)
  egress:
  - name: "allow-all-egress-to-tenant-1"
    action: "Allow"
    to:
    - pods:
        namespaces:
          namespaceSelector:
            matchLabels:
              custom-banp: tenant-1
        podSelector:
          matchLabels:
            custom-banp: tenant-1
1 The policy name must be default because BANP is a singleton object.
2 Specify the namespace to apply the ANP to.
3 BANP have both ingress and egress rules. BANP rules for spec.ingress and spec.egress fields accepts values of Deny and Allow for the action field.
4 Specify a name for the ingress.name
5 Specify the namespaces to select the pods from to apply the BANP resource.
6 Specify podSelector.matchLabels name of the pods to apply the BANP resource.

BaselineAdminNetworkPolicy Deny example

The following BANP singleton ensures that the administrator has set up a default deny policy for all ingress monitoring traffic coming into the tenants at internal security level. When combined with the "AdminNetworkPolicy Pass example", this deny policy acts as a guardrail policy for all ingress traffic that is passed by the ANP pass-monitoring policy.

Example YAML file for a guardrail Deny rule 
apiVersion: policy.networking.k8s.io/v1alpha1
kind: BaselineAdminNetworkPolicy
metadata:
  name: default
spec:
  subject:
    namespaces:
      matchLabels:
        security: internal
  ingress:
  - name: "deny-ingress-from-monitoring"
    action: "Deny"
    from:
    - namespaces:
        namespaceSelector:
          matchLabels:
            kubernetes.io/metadata.name: monitoring
# ...

You can use an AdminNetworkPolicy resource with a Pass value for the action field in conjunction with the BaselineAdminNetworkPolicy resource to create a multi-tenant policy. This multi-tenant policy allows one tenant to collect monitoring data on their application while simultaneously not collecting data from a second tenant.

As an administrator, if you apply both the "AdminNetworkPolicy Pass action example" and the "BaselineAdminNetwork Policy Deny example", tenants are then left with the ability to choose to create a NetworkPolicy resource that will be evaluated before the BANP.

For example, Tenant 1 can set up the following NetworkPolicy resource to monitor ingress traffic:

Example NetworkPolicy 
apiVersion: networking.k8s.io/v1
kind: NetworkPolicy
metadata:
  name: allow-monitoring
  namespace: tenant 1
spec:
  podSelector:
  policyTypes:
    - ingress
  ingress:
  - from:
    - namespaceSelector:
        matchLabels:
          kubernetes.io/metadata.name: monitoring
# ...

In this scenario, Tenant 1’s policy would be evaluated after the "AdminNetworkPolicy Pass action example" and before the "BaselineAdminNetwork Policy Deny example", which denies all ingress monitoring traffic coming into tenants with security level internal. With Tenant 1’s NetworkPolicy object in place, they will be able to collect data on their application. Tenant 2, however, who does not have any NetworkPolicy objects in place, will not be able to collect data. As an administrator, you have not by default monitored internal tenants, but instead, you created a BANP that allows tenants to use NetworkPolicy objects to override the default behavior of your BANP.