Red Hat OpenShift Container Platform

Deploying an egress router in redirect mode

You can deploy an egress router to redirect traffic from its own reserved source IP address to one or more destination IP addresses.

After you add an egress router, the client pods that need to use the reserved source IP address must be modified to connect to the egress router rather than connecting directly to the destination IP.

Prerequisites

You installed the OpenShift CLI (oc).
You logged in as a user with cluster-admin privileges.

Procedure

Create an egress router definition.
To ensure that other pods can find the IP address of the egress router pod, create a service that uses the egress router, as in the following example:
```
apiVersion: v1
kind: Service
metadata:
  name: egress-1
spec:
  ports:
  - name: web-app
    protocol: TCP
    port: 8080
  type: ClusterIP
  selector:
    app: egress-router-cni
```
spec.selector: Specifies the label for the egress router. The value shown is added by the Cluster Network Operator and is not configurable.

After you create the service, your pods can connect to the service. The egress router pod redirects traffic to the corresponding port on the destination IP address. The connections originate from the reserved source IP address.

Verification

View the network attachment definition that the Operator created for the egress router:
```
$ oc get network-attachment-definition egress-router-cni-nad
```
The name of the network attachment definition is not configurable.
Example output
```
NAME                    AGE
egress-router-cni-nad   18m
```

View the deployment for the egress router pod:

$ oc get deployment egress-router-cni-deployment

The name of the deployment is not configurable.

Example output

NAME                           READY   UP-TO-DATE   AVAILABLE   AGE
egress-router-cni-deployment   1/1     1            1           18m

View the status of the egress router pod:

$ oc get pods -l app=egress-router-cni

Example output

NAME                                            READY   STATUS    RESTARTS   AGE
egress-router-cni-deployment-575465c75c-qkq6m   1/1     Running   0          18m

View the logs and the routing table for the egress router pod.

Get the node name for the egress router pod:

$ POD_NODENAME=$(oc get pod -l app=egress-router-cni -o jsonpath="{.items[0].spec.nodeName}")

Enter into a debug session on the target node. This step instantiates a debug pod called <node_name>-debug:
```
$ oc debug node/$POD_NODENAME
```
Set /host as the root directory within the debug shell. The debug pod mounts the root file system of the host in /host within the pod. By changing the root directory to /host, you can run binaries from the executable paths of the host:
```
# chroot /host
```

From within the chroot environment console, display the egress router logs:

# cat /tmp/egress-router-log

Example output

2021-04-26T12:27:20Z [debug] Called CNI ADD
2021-04-26T12:27:20Z [debug] Gateway: 192.168.12.1
2021-04-26T12:27:20Z [debug] IP Source Addresses: [192.168.12.99/24]
2021-04-26T12:27:20Z [debug] IP Destinations: [80 UDP 10.0.0.99/30 8080 TCP 203.0.113.26/30 80 8443 TCP 203.0.113.27/30 443]
2021-04-26T12:27:20Z [debug] Created macvlan interface
2021-04-26T12:27:20Z [debug] Renamed macvlan to "net1"
2021-04-26T12:27:20Z [debug] Adding route to gateway 192.168.12.1 on macvlan interface
2021-04-26T12:27:20Z [debug] deleted default route {Ifindex: 3 Dst: <nil> Src: <nil> Gw: 10.128.10.1 Flags: [] Table: 254}
2021-04-26T12:27:20Z [debug] Added new default route with gateway 192.168.12.1
2021-04-26T12:27:20Z [debug] Added iptables rule: iptables -t nat PREROUTING -i eth0 -p UDP --dport 80 -j DNAT --to-destination 10.0.0.99
2021-04-26T12:27:20Z [debug] Added iptables rule: iptables -t nat PREROUTING -i eth0 -p TCP --dport 8080 -j DNAT --to-destination 203.0.113.26:80
2021-04-26T12:27:20Z [debug] Added iptables rule: iptables -t nat PREROUTING -i eth0 -p TCP --dport 8443 -j DNAT --to-destination 203.0.113.27:443
2021-04-26T12:27:20Z [debug] Added iptables rule: iptables -t nat -o net1 -j SNAT --to-source 192.168.12.99

The logging file location and logging level are not configurable when you start the egress router by creating an EgressRouter object as described in this procedure.

From within the chroot environment console, get the container ID:

# crictl ps --name egress-router-cni-pod | awk '{print $1}'

Example output

CONTAINER
bac9fae69ddb6

Determine the process ID of the container. In this example, the container ID is bac9fae69ddb6:
```
# crictl inspect -o yaml bac9fae69ddb6 | grep 'pid:' | awk '{print $2}'
```
Example output
```
68857
```
Enter the network namespace of the container:
```
# nsenter -n -t 68857
```
Display the routing table:
```
# ip route
```
In the following example output, the net1 network interface is the default route. Traffic for the cluster network uses the eth0 network interface. Traffic for the 192.168.12.0/24 network uses the net1 network interface and originates from the reserved source IP address 192.168.12.99. The pod routes all other traffic to the gateway at IP address 192.168.12.1. Routing for the service network is not shown.
Example output
```
default via 192.168.12.1 dev net1
10.128.10.0/23 dev eth0 proto kernel scope link src 10.128.10.18
192.168.12.0/24 dev net1 proto kernel scope link src 192.168.12.99
192.168.12.1 dev net1
```