12.6. Considerations for the use of an egress router pod

In redirect mode, an egress router pod sets up 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 modified to connect to the egress router rather than connecting directly to the destination IP.

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.

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 indicating which nodes are acceptable.

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.

Specifically, ensure that the following are enabled:

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: v1
kind: Deployment
metadata:
  name: egress-demo-controller
spec:
  replicas: 1 1
  selector:
    name: egress-router
  template:
    metadata:
      name: egress-router
      labels:
        name: egress-router
      annotations:
        pod.network.openshift.io/assign-macvlan: "true"
    spec: 2
      initContainers:
        ...
      containers:
        ...