This document describes how to set up an egress NAT gateway for Anthos clusters on bare metal. This gateway provides persistent, deterministic routing for the egress traffic from your clusters. When you run workloads that have egress user traffic (outside of your clusters), your customers want to identify this traffic by using a few deterministic IP addresses. This allows your customers to establish IP-based security measures, like allowlisting policies. There is no charge to use this feature while it is in preview.
The egress NAT gateway is enabled using two custom resources. For a given
AnthosNetworkGateway custom resource specifies floating IP
addresses that can be configured on the network interface of a Node that is
chosen to act as a gateway. The
EgressNatPolicy custom resource lets you
specify egress routing policies to control the traffic on the egress gateway.
If you do not set up an egress NAT gateway, or if egress traffic does not meet traffic selection rules, egress traffic from a given Pod to a destination outside your cluster is masqueraded to the IP address of the node where the Pod is running. In this scenario, there is no guarantee that all egress traffic from a particular Pod will have the same source IP address or will masquerade to the same Node IP address.
How the egress NAT gateway works
The egress traffic selection logic is based on a namespace selector, a Pod selector, and a set of destination IP address ranges in CIDR block notation. To illustrate how the egress NAT gateway works, let's consider the flow of a packet from a Pod to an external consumer and the corresponding response. Assume the Node subnet has IP addresses in the 192.168.1.0/24 CIDR block.
The following diagram shows the network architecture for egress traffic through a gateway node.
The packet flow through the egress NAT gateway might look like this:
Egress traffic is generated from a Pod with IP address
10.10.10.1in a Node with IP address
The traffic's destination address is an endpoint outside of the cluster.
If the traffic matches an egress rule, the eBPF program routes the egress traffic to the gateway Node, instead of directly masquerading with the Node IP address.
The gateway Node receives the egress traffic.
The gateway node masquerades the originating traffic's source IP address,
10.10.10.1, with the source egress IP address,
192.168.1.100specified in the
Return traffic comes back to the gateway Node with destination as
The gateway node matches the conntrack of the return traffic with that of the original egress traffic and rewrites the destination IP address as
10.10.10.1is treated as in-cluster traffic, routed to the original Node and delivered back to the original Pod.
Configuring floating IP addresses for Node traffic
The Anthos Network Gateway controller is a bundled component of Anthos clusters on bare metal. The controller manages a list of one or more floating IP addresses to use for egress traffic from Nodes in your cluster. Participating Nodes are determined by the specified namespace. The Anthos Network Gateway makes a floating IP address available at all times on a best-effort basis. If a Node using a floating IP address goes down, the Anthos Network Gateway moves the assigned IP address to the next available Node. All workload egress traffic using that IP address will move as well.
Include the Anthos Network Gateway details (annotation and spec) in the cluster configuration file when you create a new 1.8.0 cluster.
AnthosNetworkGateway custom resource
You enable the Anthos Network Gateway by using the
baremetal.cluster.gke.io/enable-anthos-network-gateway annotation in the
cluster config file when you create a cluster. Set the annotation to
shown in the following example:
apiVersion: baremetal.cluster.gke.io/v1 kind: Cluster metadata: annotations: baremetal.cluster.gke.io/enable-anthos-network-gateway: "true" name: cluster1 namespace: cluster-cluster1
When you create the
AnthosNetworkGateway custom resource, set its namespace to
the cluster namespace and specify a list of floating IP addresses, as shown in
the following example:
kind: AnthosNetworkGateway apiVersion: networking.gke.io/v1alpha1 metadata: namespace: cluster-cluster1 name: default spec: floatingIPs: - 192.168.1.100 - 192.168.1.101 - 192.168.1.102
The number of floating IP addresses you specify impacts the reliability of your
cluster. For example, an egress NAT gateway will work with only one specified
floating IP address, but a Node failure may lead to traffic disruptions. If you
add more floating IP addresses, the
AnthosNetworkGateway assigns and moves
them as needed. We recommend that you provide at least two floating IP addresses
per the L2 domain that is used in the cluster.
The controller assigns the floating IPs to Nodes based on the following criteria:
- Node subnet - the floating IP address has to match Node's subnet.
- Node role (master, worker) - worker Nodes take precedence over master Nodes when assigning floating IP addresses.
- Whether a Node has a floating IP address - the controller prioritizes assignments to Nodes that do not have a floating IP assigned already.
The address/node mapping can be found in the
status section when you get the
AnthosNetworkGateway object. Note that the
AnthosNetworkGateway object is in
the kube-system namespace. If a gateway node is down, the controller of the
AnthosNetworkGateway assigns the floating IP addresses to the next available
Verifying the gateway configuration
After you have applied your gateway configuration changes, you can use
to check the status of the gateway and retrieve the floating IP addresses
specified for the gateway.
Use the following command to check the status of the
AnthosNetworkGatewayand see how the floating IP addresses are allocated:
kubectl -n kube-system get anthosnetworkgateway.networking.gke.io default -oyaml
The response for a cluster with two nodes,
worker2might look like this:
kind: AnthosNetworkGateway apiVersion: networking.gke.io/v1alpha1 metadata: namespace: kube-system name: default spec: floatingIPs: - 192.168.1.100 - 192.168.1.101 - 192.168.1.102 status: nodes: worker1: Up worker2: Up // Or Down floatingIPs: 192.168.1.100: worker1 192.168.1.101: worker2 192.168.1.102: worker1
Use the following command to retrieve the
AnthosNetworkGatewaystatus and address allocation for a specific node.
kubectl -n kube-system get anthosnetworkgatewaynode.networking.gke.io NODE_NAME -oyaml
Replace NODE_NAME with the name of the specific node/machine that you want to inspect.
Setting traffic selection rules
EgressNATPolicy custom resource specifies traffic selection rules and
assigns a deterministic IP address for egress traffic that leaves the cluster.
When specifying the CR,
egress (with at least one rule),
egressSourceIP are all required.
kubectl apply to create the
EgressNATPolicy custom resource. The
following sections provide details and examples for defining the specification.
Specifying egress routing rules
EgressNatPolicy custom resource lets you specify the following rules for
You must specify one or more egress traffic selection rules in the
- Each rule consists of a
- Selection is based on a namespace label,
namespaceSelector.matchLabels.**user**, and a Pod label,
- If a Pod matches any of the rules (matching uses an OR relationship), it is selected for egress traffic.
- Each rule consists of a
Specify allowed destination addresses in the
destinationCIDRstakes a list of CIDR blocks.
- If outgoing traffic from a Pod has a destination IP address that falls within the range of any of the specified CIDR blocks, it is selected for egress traffic.
In the following example, egress traffic from a Pod is permitted when the following criteria are met:
- Pod is labeled with
- Pod is in a namespace labeled as either
- Pod is communicating to IP addresses in the
kind: EgressNATPolicy apiVersion: networking.gke.io/v1alpha1 metadata: name: egress spec: egress: - namespaceSelector: matchLabels: user: alice podSelector: matchLabels: role: frontend - namespaceSelector: matchLabels: user: paul podSelector: matchLabels: role: frontend destinationCIDRs: - 126.96.36.199/24 egressSourceIP: 192.168.1.100
For more information about using labels, refer to Labels and Selectors in the Kubernetes documentation.
Specifying a source IP address for egress traffic
Specify the source IP address that you want to use in the
The source IP address must match one of the floating IP addresses specified in
AnthosNetworkGateway custom resource.
EgressNATPolicy example from the preceding section, if the Pod
selection and destination IP address criteria is met, egress traffic from the
Pod is translated to
192.168.1.100 using SNAT.
In order for the route to be accepted, the
egressSourceIP address must be in
the same subnet as the gateway Node IP. If the
egressSourceIP address is
unknown (not assigned) to the gateway node, the route request can't be
fulfilled. In this case, you will get an
UnknownEgressIP error in the
Use the following
kubectl command to print the events for the
kubectl describe EgressNATPolicy egress
If there are multiple
EgressNATPolicy CRs, each must have a different
egressSourceIP address. To prevent conflicts, coordinate with the development
Egress traffic selection rules and network policies
The egress NAT gateway is compatible with network policy APIs. Network policies are assessed first and take precedence over the traffic selection rules of the egress NAT gateway. For example, if the egress traffic triggers a network policy resulting in the packet being dropped, egress gateway rules won't check the packet. Only when the network policy allows the packet to egress will the egress traffic selection rules be evaluated to decide how the traffic is handled, either using the egress NAT gateway or directly masquerading with the IP address of the Node where the Pod is running.
The current limitations for the egress NAT gateway include:
The egress NAT gateway is only enabled for IPv4 mode.
Egress IP addresses have to be in the same L2 domain with Node IP addresses for this preview.
Upgrades are not supported for clusters that have been configured to use the preview of the egress NAT gateway.