EIP and SNAT¶

This configuration is for the network under default VPC, for custom VPC please refer to VPC Gateway

Kube-OVN supports SNAT and EIP functionality at the Pod level using the L3 Gateway feature in OVN. By using SNAT, a group of Pods can share an IP address for external access. With the EIP feature, a Pod can be directly associated with an external IP. External services can access the Pod directly through the EIP, and the Pod will also access external services through this EIP.

Preparation¶

In order to use the OVN's L3 Gateway capability, a separate NIC must be bridged into the OVS bridge for overlay and underlay network communication. The host must have other NICs for management.
Since packets passing through NAT will go directly to the Underlay network, it is important to confirm that such packets can pass safely on the current network architecture.
Currently, there is no conflict detection for EIP and SNAT addresses, and an administrator needs to manually assign them to avoid address conflicts.

Create Config¶

Create ConfigMap ovn-external-gw-config in kube-system Namespace:

apiVersion: v1
kind: ConfigMap
metadata:
  name: ovn-external-gw-config
  namespace: kube-system
data:
  enable-external-gw: "true"
  external-gw-nodes: "kube-ovn-worker"
  external-gw-nic: "eth1"
  external-gw-addr: "172.56.0.1/16"
  nic-ip: "172.56.0.254/16"
  nic-mac: "16:52:f3:13:6a:25"

enable-external-gw: Whether to enable SNAT and EIP functions.
type: centrailized or distributed， Default is centralized If distributed is used, all nodes of the cluster need to have the same name NIC to perform the gateway function.
external-gw-nodes: In centralized mode，The names of the node performing the gateway role, comma separated.
external-gw-nic: The name of the NIC that performs the role of a gateway on the node.
external-gw-addr: The IP and mask of the physical network gateway.
nic-ip,nic-mac: The IP and Mac assigned to the logical gateway port needs to be an unoccupied IP and Mac for the physical subnet.

Confirm the Configuration Take Effect¶

Check the OVN-NB status to confirm that the ovn-external logical switch exists and that the correct address and chassis are bound to the ovn-cluster-ovn-external logical router port.

# kubectl ko nbctl show
switch 3de4cea7-1a71-43f3-8b62-435a57ef16a6 (ovn-external)
    port ln-ovn-external
        type: localnet
        addresses: ["unknown"]
    port ovn-external-ovn-cluster
        type: router
        router-port: ovn-cluster-ovn-external
router e1eb83ad-34be-4ed5-9a02-fcc8b1d357c4 (ovn-cluster)
    port ovn-cluster-ovn-external
        mac: "ac:1f:6b:2d:33:f1"
        networks: ["172.56.0.100/16"]
        gateway chassis: [a5682814-2e2c-46dd-9c1c-6803ef0dab66]

Check the OVS status to confirm that the corresponding NIC is bridged into the br-external bridge:

# kubectl ko vsctl ${gateway node name} show
e7d81150-7743-4d6e-9e6f-5c688232e130
    Bridge br-external
        Port br-external
            Interface br-external
                type: internal
        Port eno2
            Interface eno2
        Port patch-ln-ovn-external-to-br-int
            Interface patch-ln-ovn-external-to-br-int
                type: patch
                options: {peer=patch-br-int-to-ln-ovn-external}

Config EIP amd SNAT on Pod¶

SNAT and EIP can be configured by adding the ovn.kubernetes.io/snat or ovn.kubernetes.io/eip annotation to the Pod, respectively:

apiVersion: v1
kind: Pod
metadata:
  name: pod-gw
  annotations:
    ovn.kubernetes.io/snat: 172.56.0.200
spec:
  containers:
  - name: snat-pod
    image: docker.io/library/nginx:alpine
---
apiVersion: v1
kind: Pod
metadata:
  name: pod-gw
  annotations:
    ovn.kubernetes.io/eip: 172.56.0.233
spec:
  containers:
  - name: eip-pod
    image: docker.io/library/nginx:alpine

The EIP or SNAT rules configured by the Pod can be dynamically adjusted via kubectl or other tools, remember to remove the ovn.kubernetes.io/routed annotation to trigger the routing change.

kubectl annotate pod pod-gw ovn.kubernetes.io/eip=172.56.0.221 --overwrite
kubectl annotate pod pod-gw ovn.kubernetes.io/routed-

When the EIP or SNAT takes into effect, the ovn.kubernetes.io/routed annotation will be added back.

Advanced Configuration¶

Some args of kube-ovn-controller allow for advanced configuration of SNAT and EIP:

--external-gateway-config-ns: The Namespace of Configmap ovn-external-gw-config, default is kube-system。
--external-gateway-net: The name of the bridge to which the physical NIC is bridged, default is external.
--external-gateway-vlanid: Physical network Vlan Tag number, default is 0, i.e. no Vlan is used.

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