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Considerations for the use of an egress router pod - OpenShift SDN network plugin | Networking | OpenShift Container Platform 4.14
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Considerations for the use of an egress router pod

About an egress router pod

The OpenShift Container Platform egress router pod redirects traffic to a specified remote server from a private source IP address that is not used for any other purpose. An egress router pod can send network traffic to servers that are set up to allow access only from specific IP addresses.

The egress router pod is not intended for every outgoing connection. Creating large numbers of egress router pods can exceed the limits of your network hardware. For example, creating an egress router pod for every project or application could exceed the number of local MAC addresses that the network interface can handle before reverting to filtering MAC addresses in software.

The egress router image is not compatible with Amazon AWS, Azure Cloud, or any other cloud platform that does not support layer 2 manipulations due to their incompatibility with macvlan traffic.

Egress router modes

In redirect mode, an egress router pod configures iptables rules to redirect traffic from its own IP address to one or more destination IP addresses. Client pods that need to use the reserved source IP address must be configured to access the service for the egress router rather than connecting directly to the destination IP. You can access the destination service and port from the application pod by using the curl command. For example:

$ curl <router_service_IP> <port>

In HTTP proxy mode, an egress router pod runs as an HTTP proxy on port 8080. This mode only works for clients that are connecting to HTTP-based or HTTPS-based services, but usually requires fewer changes to the client pods to get them to work. Many programs can be told to use an HTTP proxy by setting an environment variable.

In DNS proxy mode, an egress router pod runs as a DNS proxy for TCP-based services from its own IP address to one or more destination IP addresses. To make use of the reserved, source IP address, client pods must be modified to connect to the egress router pod rather than connecting directly to the destination IP address. This modification ensures that external destinations treat traffic as though it were coming from a known source.

Redirect mode works for all services except for HTTP and HTTPS. For HTTP and HTTPS services, use HTTP proxy mode. For TCP-based services with IP addresses or domain names, use DNS proxy mode.

Egress router pod implementation

The egress router pod setup is performed by an initialization container. That container runs in a privileged context so that it can configure the macvlan interface and set up iptables rules. After the initialization container finishes setting up the iptables rules, it exits. Next the egress router pod executes the container to handle the egress router traffic. The image used varies depending on the egress router mode.

The environment variables determine which addresses the egress-router image uses. The image configures the macvlan interface to use EGRESS_SOURCE as its IP address, with EGRESS_GATEWAY as the IP address for the gateway.

Network Address Translation (NAT) rules are set up so that connections to the cluster IP address of the pod on any TCP or UDP port are redirected to the same port on IP address specified by the EGRESS_DESTINATION variable.

If only some of the nodes in your cluster are capable of claiming the specified source IP address and using the specified gateway, you can specify a nodeName or nodeSelector to identify which nodes are acceptable.

deployment considerations

An egress router pod adds an additional IP address and MAC address to the primary network interface of the node. As a result, you might need to configure your hypervisor or cloud provider to allow the additional address.

Red Hat OpenStack Platform (RHOSP)

If you deploy OpenShift Container Platform on RHOSP, you must allow traffic from the IP and MAC addresses of the egress router pod on your OpenStack environment. If you do not allow the traffic, then communication will fail:

$ openstack port set --allowed-address \
  ip_address=<ip_address>,mac_address=<mac_address> <neutron_port_uuid>
VMware vSphere

If you are using VMware vSphere, see the VMware documentation for securing vSphere standard switches. View and change VMware vSphere default settings by selecting the host virtual switch from the vSphere Web Client.

Specifically, ensure that the following are enabled:

Failover configuration

To avoid downtime, you can deploy an egress router pod with a deployment resource, as in the following example. To create a new Service object for the example deployment, use the oc expose deployment/egress-demo-controller command.

apiVersion: apps/v1
kind: deployment
metadata:
  name: egress-demo-controller
spec:
  replicas: 1 (1)
  selector:
    matchLabels:
      name: egress-router
  template:
    metadata:
      name: egress-router
      labels:
        name: egress-router
      annotations:
        pod.network.openshift.io/assign-macvlan: "true"
    spec: (2)
      initContainers:
        ...
      containers:
        ...
1 Ensure that replicas is set to 1, because only one pod can use a given egress source IP address at any time. This means that only a single copy of the router runs on a node.
2 Specify the Pod object template for the egress router pod.

Additional resources