RFE: document hostNetwork and optionally create a add pool-member-type=hostnetwork

[alonsocamaro]

Title

RFE: add pool-member-type=hostnetwork or document

Description

This is a cosmetic enhancement. The functionality is already implemented.

By default OpenShift's ingress controller (aka OpenShift Router, HA-proxy) is deployed neither using nodePort or clusterIP but instead using hostNetwork. This can be checked with:

oc -n openshift-ingress get pods router-default-7ffcd9d86b-r4fvr -o=jsonpath='{.spec.hostNetwork}'

This is configured in the operator as shown in [1] below.

This method is also used by other ingress controllers like NGINX+ IC. See for example the controller.hostNetwork variable in https://docs.nginx.com/nginx-ingress-controller/installation/installing-nic/installation-with-helm/

We don´t provide instructions on how these deployments should be configured.

I found that using clusterIP works as desired, using the node's IPs of the nodes where the PODs are deployed:

[cloud-user@ocp-provisioner routes-bigip]$ oc -n openshift-ingress get pods -o wide
NAME                              READY   STATUS    RESTARTS      AGE   IP          NODE                      NOMINATED NODE   READINESS GATES
router-default-7ffcd9d86b-r4fvr   1/1     Running   8 (34m ago)   68d   10.1.10.7   master-2.ocp.f5-udf.com   <none>           <none>
router-default-7ffcd9d86b-rcptz   1/1     Running   8 (34m ago)   68d   10.1.10.8   master-3.ocp.f5-udf.com   <none>           <none>

[cloud-user@ocp-provisioner routes-bigip]$ oc -n openshift-ingress get ep router-default-route-a -o yaml
apiVersion: v1
kind: Endpoints
metadata:
  annotations:
    endpoints.kubernetes.io/last-change-trigger-time: "2024-05-15T07:45:14Z"
  creationTimestamp: "2024-05-15T07:45:14Z"
  name: router-default-route-a
  namespace: openshift-ingress
  resourceVersion: "7878697"
  uid: 10ea9494-0aeb-49c4-a90b-1bfd25d75128
subsets:
- addresses:
  - ip: 10.1.10.7
    nodeName: master-2.ocp.f5-udf.com
    targetRef:
      kind: Pod
      name: router-default-7ffcd9d86b-r4fvr
      namespace: openshift-ingress
      uid: 8da16f47-a967-49b6-9509-26139dc40397
  - ip: 10.1.10.8
    nodeName: master-3.ocp.f5-udf.com
    targetRef:
      kind: Pod
      name: router-default-7ffcd9d86b-rcptz
      namespace: openshift-ingress
      uid: 6b65aa98-1335-4335-bc23-1d2c380e15bc
  ports:
  - name: https
    port: 443
    protocol: TCP
  - name: http
    port: 80
    protocol: TCP

[cloud-user@ocp-provisioner routes-bigip]$ oc get nodes -o wide
NAME                      STATUS   ROLES                         AGE    VERSION            INTERNAL-IP   EXTERNAL-IP   OS-IMAGE                                                        KERNEL-VERSION                 CONTAINER-RUNTIME
master-1.ocp.f5-udf.com   Ready    control-plane,master,worker   333d   v1.25.10+3fe2906   10.1.10.6     <none>        Red Hat Enterprise Linux CoreOS 412.86.202305310359-0 (Ootpa)   4.18.0-372.58.1.el8_6.x86_64   cri-o://1.25.3-5.rhaos4.12.git44a2cb2.el8
master-2.ocp.f5-udf.com   Ready    control-plane,master,worker   333d   v1.25.10+3fe2906   10.1.10.7     <none>        Red Hat Enterprise Linux CoreOS 412.86.202305310359-0 (Ootpa)   4.18.0-372.58.1.el8_6.x86_64   cri-o://1.25.3-5.rhaos4.12.git44a2cb2.el8
master-3.ocp.f5-udf.com   Ready    control-plane,master,worker   333d   v1.25.10+3fe2906   10.1.10.8     <none>        Red Hat Enterprise Linux CoreOS 412.86.202305310359-0 (Ootpa)   4.18.0-372.58.1.el8_6.x86_64   cri-o://1.25.3-5.rhaos4.12.git44a2cb2.el8
worker-1.ocp.f5-udf.com   Ready    worker                        333d   v1.25.10+3fe2906   10.1.10.9     <none>        Red Hat Enterprise Linux CoreOS 412.86.202305310359-0 (Ootpa)   4.18.0-372.58.1.el8_6.x86_64   cri-o://1.25.3-5.rhaos4.12.git44a2cb2.el8
worker-2.ocp.f5-udf.com   Ready    worker                        333d   v1.25.10+3fe2906   10.1.10.10    <none>        Red Hat Enterprise Linux CoreOS 412.86.202305310359-0 (Ootpa)   4.18.0-372.58.1.el8_6.x86_64   cri-o://1.25.3-5.rhaos4.12.git44a2cb2.el8

Actual Problem

This is not documented.

Solution Proposed

This should be documented and optionally it might be worth considering if an option pool-member-type=hostnetwork being an alias pool-member-type=cluster is worth adding for clarity

Additional context

[1]

oc -n openshift-ingress-operator get ingresscontroller default -o yaml
[...]
  endpointPublishingStrategy:
    hostNetwork:
      httpPort: 80
      httpsPort: 443
      protocol: TCP
      statsPort: 1936
    type: HostNetwork

[alonsocamaro]

A non-cosmetic reason to implement pool-member-type=hostnetwork is because when using hostnetwork and the OVN CNI, we don´t need to create static routes to the cluster IPs, which might not be even directly connected. That is, the static routes might fail to be created.

[trinaths]

Created [CONTCNTR-4747] for internal tracking.