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Configuring an egress IP address

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As a cluster administrator, you can configure the OVN-Kubernetes Container Network Interface (CNI) network plugin to assign one or more egress IP addresses to a namespace, or to specific pods in a namespace.

Egress IP address architectural design and implementation

The Red Hat OpenShift Service on AWS egress IP address functionality allows you to ensure that the traffic from one or more pods in one or more namespaces has a consistent source IP address for services outside the cluster network.

For example, you might have a pod that periodically queries a database that is hosted on a server outside of your cluster. To enforce access requirements for the server, a packet filtering device is configured to allow traffic only from specific IP addresses. To ensure that you can reliably allow access to the server from only that specific pod, you can configure a specific egress IP address for the pod that makes the requests to the server.

An egress IP address assigned to a namespace is different from an egress router, which is used to send traffic to specific destinations.

In ROSA with HCP clusters, application pods and ingress router pods run on the same node. If you configure an egress IP address for an application project in this scenario, the IP address is not used when you send a request to a route from the application project.

The assignment of egress IP addresses to control plane nodes with the EgressIP feature is not supported.

The following examples illustrate the annotation from nodes on several public cloud providers. The annotations are indented for readability.

Example cloud.network.openshift.io/egress-ipconfig annotation on AWS
cloud.network.openshift.io/egress-ipconfig: [
  {
    "interface":"eni-078d267045138e436",
    "ifaddr":{"ipv4":"10.0.128.0/18"},
    "capacity":{"ipv4":14,"ipv6":15}
  }
]

The following sections describe the IP address capacity for supported public cloud environments for use in your capacity calculation.

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Amazon Web Services (AWS) IP address capacity limits

On AWS, constraints on IP address assignments depend on the instance type configured. For more information, see IP addresses per network interface per instance type

Assignment of egress IPs to pods

To assign one or more egress IPs to a namespace or specific pods in a namespace, the following conditions must be satisfied:

  • At least one node in your cluster must have the k8s.ovn.org/egress-assignable: "" label.

  • An EgressIP object exists that defines one or more egress IP addresses to use as the source IP address for traffic leaving the cluster from pods in a namespace.

If you create EgressIP objects prior to labeling any nodes in your cluster for egress IP assignment, Red Hat OpenShift Service on AWS might assign every egress IP address to the first node with the k8s.ovn.org/egress-assignable: "" label.

To ensure that egress IP addresses are widely distributed across nodes in the cluster, always apply the label to the nodes you intent to host the egress IP addresses before creating any EgressIP objects.

Assignment of egress IPs to nodes

When creating an EgressIP object, the following conditions apply to nodes that are labeled with the k8s.ovn.org/egress-assignable: "" label:

  • An egress IP address is never assigned to more than one node at a time.

  • An egress IP address is equally balanced between available nodes that can host the egress IP address.

  • If the spec.EgressIPs array in an EgressIP object specifies more than one IP address, the following conditions apply:

    • No node will ever host more than one of the specified IP addresses.

    • Traffic is balanced roughly equally between the specified IP addresses for a given namespace.

  • If a node becomes unavailable, any egress IP addresses assigned to it are automatically reassigned, subject to the previously described conditions.

When a pod matches the selector for multiple EgressIP objects, there is no guarantee which of the egress IP addresses that are specified in the EgressIP objects is assigned as the egress IP address for the pod.

Additionally, if an EgressIP object specifies multiple egress IP addresses, there is no guarantee which of the egress IP addresses might be used. For example, if a pod matches a selector for an EgressIP object with two egress IP addresses, 10.10.20.1 and 10.10.20.2, either might be used for each TCP connection or UDP conversation.

Architectural diagram of an egress IP address configuration

The following diagram depicts an egress IP address configuration. The diagram describes four pods in two different namespaces running on three nodes in a cluster. The nodes are assigned IP addresses from the 192.168.126.0/18 CIDR block on the host network.

Architectural diagram for the egress IP feature.

Both Node 1 and Node 3 are labeled with k8s.ovn.org/egress-assignable: "" and thus available for the assignment of egress IP addresses.

The dashed lines in the diagram depict the traffic flow from pod1, pod2, and pod3 traveling through the pod network to egress the cluster from Node 1 and Node 3. When an external service receives traffic from any of the pods selected by the example EgressIP object, the source IP address is either 192.168.126.10 or 192.168.126.102. The traffic is balanced roughly equally between these two nodes.

The following resources from the diagram are illustrated in detail:

Namespace objects

The namespaces are defined in the following manifest:

Namespace objects
apiVersion: v1
kind: Namespace
metadata:
  name: namespace1
  labels:
    env: prod
---
apiVersion: v1
kind: Namespace
metadata:
  name: namespace2
  labels:
    env: prod
EgressIP object

The following EgressIP object describes a configuration that selects all pods in any namespace with the env label set to prod. The egress IP addresses for the selected pods are 192.168.126.10 and 192.168.126.102.

EgressIP object
apiVersion: k8s.ovn.org/v1
kind: EgressIP
metadata:
  name: egressips-prod
spec:
  egressIPs:
  - 192.168.126.10
  - 192.168.126.102
  namespaceSelector:
    matchLabels:
      env: prod
status:
  items:
  - node: node1
    egressIP: 192.168.126.10
  - node: node3
    egressIP: 192.168.126.102

For the configuration in the previous example, Red Hat OpenShift Service on AWS assigns both egress IP addresses to the available nodes. The status field reflects whether and where the egress IP addresses are assigned.

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EgressIP object

The following YAML describes the API for the EgressIP object. The scope of the object is cluster-wide; it is not created in a namespace.

apiVersion: k8s.ovn.org/v1
kind: EgressIP
metadata:
  name: <name> (1)
spec:
  egressIPs: (2)
  - <ip_address>
  namespaceSelector: (3)
    ...
  podSelector: (4)
    ...
1 The name for the EgressIPs object.
2 An array of one or more IP addresses.
3 One or more selectors for the namespaces to associate the egress IP addresses with.
4 Optional: One or more selectors for pods in the specified namespaces to associate egress IP addresses with. Applying these selectors allows for the selection of a subset of pods within a namespace.

The following YAML describes the stanza for the namespace selector:

Namespace selector stanza
namespaceSelector: (1)
  matchLabels:
    <label_name>: <label_value>
1 One or more matching rules for namespaces. If more than one match rule is provided, all matching namespaces are selected.

The following YAML describes the optional stanza for the pod selector:

Pod selector stanza
podSelector: (1)
  matchLabels:
    <label_name>: <label_value>
1 Optional: One or more matching rules for pods in the namespaces that match the specified namespaceSelector rules. If specified, only pods that match are selected. Others pods in the namespace are not selected.

In the following example, the EgressIP object associates the 192.168.126.11 and 192.168.126.102 egress IP addresses with pods that have the app label set to web and are in the namespaces that have the env label set to prod:

Example EgressIP object
apiVersion: k8s.ovn.org/v1
kind: EgressIP
metadata:
  name: egress-group1
spec:
  egressIPs:
  - 192.168.126.11
  - 192.168.126.102
  podSelector:
    matchLabels:
      app: web
  namespaceSelector:
    matchLabels:
      env: prod

In the following example, the EgressIP object associates the 192.168.127.30 and 192.168.127.40 egress IP addresses with any pods that do not have the environment label set to development:

Example EgressIP object
apiVersion: k8s.ovn.org/v1
kind: EgressIP
metadata:
  name: egress-group2
spec:
  egressIPs:
  - 192.168.127.30
  - 192.168.127.40
  namespaceSelector:
    matchExpressions:
    - key: environment
      operator: NotIn
      values:
      - development
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Labeling a node to host egress IP addresses

You can apply the k8s.ovn.org/egress-assignable="" label to a node in your cluster so that Red Hat OpenShift Service on AWS can assign one or more egress IP addresses to the node.

Prerequisites

  • Install the ROSA CLI (rosa).

  • Log in to the cluster as a cluster administrator.

Procedure

  • To label a node so that it can host one or more egress IP addresses, enter the following command:

    $ rosa edit machinepool <machinepool_name> --cluster=<cluster_name> --labels "k8s.ovn.org/egress-assignable="

    This command replaces any exciting node labels on your machinepool. You should include any of the desired labels to the --labels field to ensure that your existing node labels persist.
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Next steps

Additional resources