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Document a workaround for using EgressSeparateSubnet feature on OCP #6622

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Aug 22, 2024
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Document a workaround for using EgressSeparateSubnet feature on OCP #6622

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39 changes: 39 additions & 0 deletions docs/egress.md
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@
- [Egress on Cloud](#egress-on-cloud)
- [AWS](#aws)
- [Limitations](#limitations)
- [Known issues](#known-issues)
<!-- /toc -->

## What is Egress?
Expand Down Expand Up @@ -462,3 +463,41 @@ configuration is required by some Service load balancing solutions including:
[Antrea Service external IP management, MetalLB](service-loadbalancer.md#interoperability-with-kube-proxy-ipvs-mode),
and kube-vip. It means Antrea Egress cannot work together with these solutions
in a cluster using `kube-proxy` IPVS. The issue was fixed in Antrea v1.7.0.

## Known issues

To support `EgressSeparateSubnet` feature, VLAN sub-interfaces will be created by
Antrea Agents, the `rp_filter` of VLAN sub-interfaces should be 2, which enables loose
mode filtering. In a vanilla Kubernetes cluster, Antrea Agents will set the `rp_filter`
to 2 automatically without user intervention. However, it has been observed that
`rp_filter` update by Antrea has no effect on OpenShift clusters due to [a known issue](https://github.com/antrea-io/antrea/issues/6546).
A workaround is to leverage OpenShift Node Tuning Operator to update the `rp_filter`
for `all` interface on all Egress Nodes:

```yaml
apiVersion: tuned.openshift.io/v1
kind: Tuned
metadata:
name: antrea
namespace: openshift-cluster-node-tuning-operator
spec:
profile:
- data: |
[main]
summary=Update rp_filter for all
[sysctl]
net.ipv4.conf.all.rp_filter=2
name: openshift-antrea
recommend:
- match:
- label: network-role
value: egress-gateway
priority: 10
profile: openshift-antrea
```

After you apply above `Tuned` CR named `antrea` in a given OpenShift cluster, the Node
Tuning Operator will watch the CR and update `net.ipv4.conf.all.rp_filter` to 2 for all
matched Nodes (e.g. all Nodes with a label `network-role=egress-gateway`). Please refer
to the OpenShift official document about [Using the Node Tuning Operator](https://docs.openshift.com/container-platform/4.16/scalability_and_performance/using-node-tuning-operator.html)
for more details of `Tuned` CR.