Antrea Policy CRDs

Table of Contents

• Summary
• Tier
  • Tier CRDs
  • Static Tiers
• ClusterNetworkPolicy
  • The ClusterNetworkPolicy resource
  • Behavior of to and from selectors
  • Key differences from K8s NetworkPolicy
• Antrea NetworkPolicy
  • The Antrea NetworkPolicy resource
  • Key differences from ClusterNetworkPolicy
• Antrea Policy ordering based on priorities
  • Ordering based on Tier priority
  • Ordering based on policy priority
  • Rule enforcement based on priorities
• RBAC
• Notes
• Known Issues

Summary

Antrea supports standard K8s NetworkPolicies to secure traffic between Pods. These NetworkPolicies are written from an application developer's perspective, hence they lack the ability to gain a finer-grained control over the security policies that a cluster administrator would require. This document describes a few new CRDs supported by Antrea to provide the administrator with more control over security within the cluster, and which are meant to co-exist with and complement the K8s NetworkPolicy.

Tier

Antrea supports grouping Antrea Policy CRDs together in a tiered fashion to provide a hierarchy of security policies. This is achieved by setting the tier field when defining an Antrea Policy CRD (e.g. a ClusterNetworkPolicy object) to the appropriate tier name. Each tier has a priority associated with it, which determines its relative order among all tiers.

Note: K8s NetworkPolicies will be enforced once all tiers have been enforced.

Tier CRDs

Creating Tiers as CRDs allows users the flexibility to create and delete Tiers as per their preference i.e. not be bound to 5 static tiering options as was the case initially.

An example Tier might look like this:

apiVersion: security.antrea.tanzu.vmware.com/v1alpha1
kind: Tier
metadata:
  name: mytier
spec:
  priority: 10
  description: "my custom tier"

Tiers have the following characteristics:

• Policies can associate themselves with an existing Tier by setting the tier field in a Antrea NetworkPolicy CRD spec to the Tier's name.
• A Tier must exist before an Antrea policy can reference it.
• Policies associated with higher ordered (low priority value) Tiers are enforced first.
• No two Tiers can be created with the same priority.
• Updating the Tier's priority field is unsupported.
• Deleting Tier with existing references from policies is not allowed.

Static tiers

Antrea release 0.9.x introduced support for 5 static tiers. These static tiers have been removed in favor of Tier CRDs as mentioned in the previous section. On startup, antrea-controller will create 5 Read-Only Tier resources corresponding to the static tiers for default consumption as shown below.

    Emergency -> Tier name "emergency" with priority "5"
    SecurityOps -> Tier name "securityops" with priority "50"
    NetworkOps -> Tier name "networkops" with priority "100"
    Platform -> Tier name "platform" with priority "150"
    Application -> Tier name "application" with priority "250"

Any Antrea policy CRD referencing a static tier in its spec will now internally reference the corresponding Tier resource, thus maintaining the order of enforcement.

Previously, the static tiers created were as follows in the relative order of precedence:

    Emergency > SecurityOps > NetworkOps > Platform > Application  

Thus, all Antrea Policy resources associated with "Emergency" tier will be enforced before any other Antrea Policy resource associated with any other tier, until a match occurs, in which case the policy rule's action will be applied. The "Application" tier carries the lowest precedence, and any Antrea Policy resource without a tier name set in its spec will be associated with the "Application" tier. Even though the policies associated with the "Application" tier carry the lowest precedence amongst all the tiers, they are still enforced before K8s NetworkPolicies. Thus, admin-created tiered Antrea Policy CRDs have a higher precedence than developer-created K8s NetworkPolicies.

ClusterNetworkPolicy

ClusterNetworkPolicy, one of the two Antrea Policy CRDs introduced, is a specification of how workloads within a cluster communicate with each other and other external endpoints. The ClusterNetworkPolicy is supposed to aid cluster admins to configure the security policy for the cluster, unlike K8s NetworkPolicy, which is aimed towards developers to secure their apps and affects Pods within the Namespace in which the K8s NetworkPolicy is created. Rules belonging to ClusterNetworkPolicies are enforced before any rule belonging to a K8s NetworkPolicy.

Note: ClusterNetworkPolicy is currently in "Alpha" stage. In order to enable them, edit the Controller and Agent configuration in the antrea ConfigMap as follows:

   antrea-controller.conf: |
     featureGates:
       # Enable AntreaPolicy feature to complement K8s NetworkPolicy
       # for cluster admins to define security policies which apply to the
       # entire cluster.
       AntreaPolicy: true

   antrea-agent.conf: |
     featureGates:
       # Enable AntreaPolicy feature to complement K8s NetworkPolicy
       # for cluster admins to define security policies which apply to the
       # entire cluster.
       AntreaPolicy: true

The ClusterNetworkPolicy resource

An example ClusterNetworkPolicy might look like this:

apiVersion: security.antrea.tanzu.vmware.com/v1alpha1
kind: ClusterNetworkPolicy
metadata:
  name: test-cnp
spec:
    priority: 5
    tier: securityops
    appliedTo:
      - podSelector:
          matchLabels:
            role: db
      - namespaceSelector:
          matchLabels:
            env: prod
    ingress:
      - action: Allow
        from:
          - podSelector:
              matchLabels:
                role: frontend
          - podSelector:
              matchLabels:
                role: nondb
            namespaceSelector:
              matchLabels:
                role: db
        ports:
          - protocol: TCP
            port: 8080
    egress:
      - action: Drop
        to:
          - ipBlock:
              cidr: 10.0.10.0/24
        ports:
          - protocol: TCP
            port: 5978

spec: The ClusterNetworkPolicy spec has all the information needed to define a cluster-wide security policy.

appliedTo: The appliedTo field specifies the grouping criteria of Pods to which the policy applies to. Pods can be selected cluster-wide using podSelector. If set with a namespaceSelector, all Pods from Namespaces selected by the namespaceSelector will be selected. Specific Pods from specific Namespaces can be selected by providing both a podSelector and a namespaceSelector in the same appliedTo entry. IPBlock cannot be set in the appliedTo field. In the example, the policy applies to Pods, which either match the labels "role=db" in all the Namespaces, or are from Namespaces which match the labels "env=prod".

priority: The priority field determines the relative priority of the policy among all ClusterNetworkPolicies in the given cluster. This field is mandatory. A lower priority value indicates higher precedence. Priority values can range from 1.0 to 10000.0. Note: Policies with the same priorities will be enforced indeterministically. Users should therefore take care to use priorities to ensure the behavior they expect.

tier: The tier field associates a CNP to an existing Tier. The tier field can be set with the name of the Tier CRD to which this policy must be associated with. If not set, the CNP is associated with the lowest priority default tier i.e. the "application" Tier.

ingress: Each ClusterNetworkPolicy may consist of zero or more ordered set of ingress rules. Each rule, depending on the action field of the rule, allows or drops traffic which matches both the from and ports sections. The example policy contains a single rule, which allows matched traffic on a single port, from one of two sources: the first specified by a podSelector and the second specified by a combination of a podSelector and a namespaceSelector. Note: The order in which the ingress rules are set matter, i.e. rules will be enforced in the order in which they are written.

egress: Each ClusterNetworkPolicy may consist of zero or more ordered set of egress rules. Each rule, depending on the action field of the rule, allows or drops traffic which matches both the to and ports sections. The example policy contains a single rule, which drops matched traffic on a single port, to the 10.0.10.0/24 subnet specified by the ipBlock field. Note: The order in which the egress rules are set matter, i.e. rules will be enforced in the order in which they are written.

Behavior of to and from selectors

There are four kinds of selectors that can be specified in an ingress from section or egress to section:

podSelector: This selects particular Pods from all Namespaces as "sources", if set in ingress section, or as "destinations", if set in egress section.

namespaceSelector: This selects particular Namespaces for which all Pods are grouped as ingress "sources" or egress "destinations".

podSelector and namespaceSelector: A single to/from entry that specifies both namespaceSelector and podSelector selects particular Pods within particular Namespaces.

ipBlock: This selects particular IP CIDR ranges to allow as ingress "sources" or egress "destinations". These should be cluster-external IPs, since Pod IPs are ephemeral and unpredictable.

Key differences from K8s NetworkPolicy

• ClusterNetworkPolicy is at the cluster scope, hence a podSelector without any namespaceSelector selects Pods from all Namespaces.
• There is no automatic isolation of Pods on being selected in appliedTo.
• Ingress/Egress rules in ClusterNetworkPolicy has an action field which specifies whether the matched rule allows or drops the traffic.
• IPBlock field in the ClusterNetworkPolicy rules do not have the except field. A higher priority rule can be written to deny the specific CIDR range to simulate the behavior of IPBlock field with cidr and except set.
• Rules assume the priority in which they are written. i.e. rule set at top takes precedence over a rule set below it.

Antrea NetworkPolicy

Antrea NetworkPolicy is another Policy CRD, which is similar to the ClusterNetworkPolicy CRD, however its scope is limited to a Namespace. The purpose of introducing this CRD is to allow admins to take advantage of advanced NetworkPolicy features and apply them within a Namespace to complement the K8s NetworkPolicies. Similar to the ClusterNetworkPolicy resource, Antrea NetworkPolicy can also be associated with Tiers.

Note: Antrea NetworkPolicy is currently in "Alpha" stage and is enabled along with Tiers and ClusterNetworkPolicy as part of the AntreaPolicy feature gate.

The Antrea NetworkPolicy resource

An example Antrea NetworkPolicy might look like this:

apiVersion: security.antrea.tanzu.vmware.com/v1alpha1
kind: NetworkPolicy
metadata:
  name: test-anp
  namespace: default
spec:
    priority: 5
    tier: securityops
    appliedTo:
      - podSelector:
          matchLabels:
            role: db
    ingress:
      - action: Allow
        from:
          - podSelector:
              matchLabels:
                role: frontend
          - podSelector:
              matchLabels:
                role: nondb
            namespaceSelector:
              matchLabels:
                role: db
        ports:
          - protocol: TCP
            port: 8080
    egress:
      - action: Drop
        to:
          - ipBlock:
              cidr: 10.0.10.0/24
        ports:
          - protocol: TCP
            port: 5978

Key differences from ClusterNetworkPolicy

Antrea NetworkPolicy shares it's spec with ClusterNetworkPolicy. However, the following documents some of the key differences between the two Antrea Policy CRDs.

• Antrea NetworkPolicy is Namespaced while ClusterNetworkPolicy operates at cluster scope.
• Unlike the appliedTo in a ClusterNetworkPolicy, setting a namespaceSelector in the appliedTo field is forbidden.
• podSelector without a namespaceSelector, set within a NetworkPolicy Peer of any rule, selects Pods from the Namespace in which the Antrea NetworkPolicy is created. This behavior is similar to the K8s NetworkPolicy.

Antrea Policy ordering based on priorities

Antrea Policy CRDs are ordered based on priorities set at various levels.

Ordering based on Tier priority

With the introduction of tiers, Antrea Policies, like ClusterNetworkPolicies, are first enforced based on the Tier to which they are associated. i.e. all policies belonging to a high Tier are enforced first, followed by policies belonging to the next Tier and so on, until the "application" Tier policies are enforced.

Ordering based on policy priority

Within a tier, Antrea Policy CRDs are ordered by the priority at the policy level. Thus, the policy with the highest precedence (lowest priority number value) is enforced first. This ordering is performed solely based on the priority assigned as opposed to the "Kind" of the resource, i.e. the relative ordering between a ClusterNetworkPolicy resource and an Antrea NetworkPolicy resource within a Tier depends only on the priority set in each of the two resources.

Rule enforcement based on priorities

Within a policy, rules are enforced in the order in which they are set. For example, consider the following:

• CNP1{tier: application, priority: 10, ingressRules: [ir1.1, ir1.2], egressRules: [er1.1, er1.2]}
• ANP1{tier: application, priority: 15, ingressRules: [ir2.1, ir2.2], egressRules: [er2.1, er2.2]}
• CNP3{tier: emergency, priority: 20, ingressRules: [ir3.1, ir3.2], egressRules: [er3.1, er3.2]}

This translates to the following order: - Ingress rules: ir3.1 > ir3.2 > ir1.1 -> ir1.2 -> ir2.1 -> ir2.2 - Egress rules: er3.1 > er3.2 > er1.1 -> er1.2 -> er2.1 -> er2.2

Once a rule is matched, it is executed based on the action set. If none of the policy rules match, the packet is then enforced for rules created for K8s NP. Hence, Antrea Policy CRDs take precedence over K8s NP.

RBAC

Antrea Policy CRDs are meant for admins to manage the security of their cluster. Thus, access to manage these CRDs must be granted to subjects which have the authority to outline the security policies for the cluster and/or Namespaces. On cluster initialization, Antrea grants the permissions to edit these CRDs with admin and the edit ClusterRole. In addition to this, Antrea also grants the permission to view these CRDs with the view ClusterRole. Cluster admins can therefore grant these ClusterRoles to any subject who may be responsible to manage the Antrea Policy CRDs. The admins may also decide to share the view ClusterRole to a wider range of subjects to allow them to read the policies that may affect their workloads.

Notes

• There is a soft limit of 20 on the maximum number of Tier resources that are supported. But for optimal performance, it is recommended that the number of Tiers in a cluster be less than or equal to 10.
• The v1alpha1 Policy CRDs support up to 10000 unique priority at policy level. In order to reduce the churn in the agent, it is recommended to set the priority within the range 1.0 to 100.0.

Known Issues

• Creating an Antrea NetworkPolicy with the same name as a K8s NetworkPolicy under the same Namespace creates a collision and causes unexpected behavior. See issue 1173 for more details.