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Configuring an egress firewall for a project

How an EgressNetworkPolicy custom resource works in a project

As a cluster administrator, you can use an egress firewall to limit the external hosts that some or all pods can access from within the cluster. You configure an egress firewall policy by creating an EgressNetworkPolicy custom resource (CR).

An egress firewall supports the following scenarios:

  • A pod can only connect to internal hosts and cannot start connections to the public internet.

  • A pod can only connect to the public internet and cannot start connections to internal hosts that are outside the OKD cluster.

  • A pod cannot reach specified internal subnets or hosts outside the OKD cluster.

  • A pod can only connect to specific external hosts.

For example, you can allow one project access to a specified IP range but deny the same access to a different project. Or you can restrict application developers from updating from Python pip mirrors, and force updates to come only from approved sources.

In your EgressNetworkPolicy CR you can match network traffic that meets any of the following criteria:

  • An IP address range in CIDR format

  • A DNS name that resolves to an IP address

Limitations of an EgressNetworkPolicy CR

An egress firewall has the following limitations:

  • No project can have more than one EgressNetworkPolicy CR. The creation of more than one EgressNetworkPolicy CR is allowed, however; it should not be done. When you create more than one custom resource, you receive the following message: dropping all rules. In actuality, all external traffic is dropped, which can cause security risks for your organization.

  • You must have OpenShift SDN configured to use either the network policy or multitenant mode to configure an egress firewall. If you use network policy mode, an egress firewall is compatible with only one policy per namespace and will not work with projects that share a network, such as global projects.

  • A maximum of one EgressNetworkPolicy CR with a maximum of 1,000 rules can be defined per project.

  • The default project cannot use an egress firewall.

  • When using the OpenShift SDN network plugin in multitenant mode, the following limitations apply:

    • Global projects cannot use an egress firewall. You can make a project global by using the oc adm pod-network make-projects-global command.

    • Projects merged by using the oc adm pod-network join-projects command cannot use an egress firewall in any of the joined projects.

  • If you create a selectorless service and manually define endpoints or EndpointSlices that point to external IPs, traffic to the service IP might still be allowed, even if your EgressNetworkPolicy is configured to deny all egress traffic. This occurs because OpenShift SDN does not fully enforce egress network policies for these external endpoints. Consequently, this might result in unexpected access to external services.

  • Egress firewall does not apply to the host network namespace. Pods with host networking enabled are unaffected by egress firewall rules.

  • Egress firewall rules do not apply to traffic that goes through routers. Any user with permission to create a Route CR object can bypass egress firewall policy rules by creating a route that points to a forbidden destination.

Violating any of these restrictions results in a broken egress firewall for the project. As a result, all external network traffic drops, which can cause security risks for your organization.

You can create an Egress Firewall resource in the kube-node-lease, kube-public, kube-system, openshift and openshift- projects.

Matching order for EgressNetworkPolicy CR rules

The OVN-Kubernetes network plugin evaluates egress firewall policy rules based on the first-to-last order of how you defined the rules. The first rule that matches an egress connection from a pod applies. The plugin ignores any subsequent rules for that connection.

How Domain Name Server (DNS) resolution works

If you use DNS names in any of your egress firewall policy rules, proper resolution of the domain names is subject to the following restrictions:

  • Domain name updates are polled based on a time-to-live (TTL) duration. By default, the duration is 30 seconds. When the egress firewall controller queries the local name servers for a domain name, if the response includes a TTL that is less than 30 seconds, the controller sets the duration to the returned value. If the TTL in the response is greater than 30 minutes, the controller sets the duration to 30 minutes. If the TTL is between 30 seconds and 30 minutes, the controller ignores the value and sets the duration to 30 seconds.

  • The pod must resolve the domain from the same local name servers when necessary. Otherwise the IP addresses for the domain known by the egress firewall controller and the pod can be different. If the IP addresses for a hostname differ, consistent enforcement of the egress firewall does not apply.

  • Because the egress firewall controller and pods asynchronously poll the same local name server, the pod might obtain the updated IP address before the egress controller does, which causes a race condition. Due to this current limitation, domain name usage in EgressNetworkPolicy CR is only recommended for domains with infrequent IP address changes.

  • Using DNS names in your EgressNetworkPolicy CR does not affect local DNS resolution through CoreDNS.

    However, if your policy uses domain names, and an external DNS server handles DNS resolution for an affected pod, you must include egress firewall rules that permit access to the IP addresses of your DNS server.

EgressNetworkPolicy custom resource (CR)

You can define one or more rules for an egress firewall. A rule is either an Allow rule or a Deny rule, with a specification for the traffic that the rule applies to.

The following YAML describes an EgressNetworkPolicy CR:

apiVersion: network.openshift.io/v1
kind: EgressNetworkPolicy
metadata:
  name:
spec:
  egress:
  ...

where:

<name>

Specifies the name for your egress firewall policy.

<egress>

Specifies a collection of one or more egress network policy rules as described in the following section.

EgressNetworkPolicy rules

The user can select either an IP address range in CIDR format, a domain name, or use the nodeSelector to allow or deny egress traffic. The egress stanza expects an array of one or more objects. The following YAML describes an egress firewall rule object.

egress:
- type: <type>
  to:
    cidrSelector: <cidr>
    dnsName: <dns_name>
    nodeSelector: <label_name>: <label_value>

where:

<type>

Specifies the type of rule. The value must be either Allow or Deny.

<to>

Specifies a stanza describing an egress traffic match rule that specifies the cidrSelector field or the dnsName field. You cannot use both fields in the same rule.

<cidr_range>

Specifies an IP address range in CIDR format.

<dns_name>

Specifies a DNS domain name.

<nodeSelector>

Specifies labels which are key and value pairs that the user defines. Labels are attached to objects, such as pods. The nodeSelector allows for one or more node labels to be selected and attached to pods.

Example EgressNetworkPolicy CR objects

The following example defines several egress firewall rules:

apiVersion: k8s.ovn.org/v1
kind: EgressNetworkPolicy
metadata:
  name: default
spec:
  egress: (1)
  - type: Allow
    to:
      cidrSelector: 1.2.3.0/24
  - type: Deny
    to:
      cidrSelector: 0.0.0.0/0

+ where:

<egress>

Specifies a collection of egress firewall policy rule objects.

Creating an EgressNetworkPolicy custom resource (CR)

As a cluster administrator, you can create an EgressNetworkPolicy CR for a project.

If the project already has an EgressNetworkPolicy object defined, you must edit the existing policy to make changes to the egress firewall rules.
Prerequisites

  • A cluster that uses the OpenShift SDN network plugin.

  • Install the OpenShift CLI (oc).

  • You must log in to the cluster as a cluster administrator.

Procedure

  1. Create a policy rule:

    1. Create a <policy_name>.yaml file where <policy_name> describes the egress policy rules.

    2. Define the EgressNetworkPolicy in the file.

  2. Create the policy object by entering the following command. Replace <policy_name> with the name of the policy and <project> with the project that the rule applies to.

    $ oc create -f <policy_name>.yaml -n <project>

    Successful output lists the egressnetworkpolicy.network.openshift.io/v1 name and the created status.

  3. Optional: Save the <policy_name>.yaml file so that you can make changes later.