Egress: There is downtime on startup new NAT clients

[terassyi]

What

When we create a new NAT client, there is slight downtime because of the time lag in configuring a link and a route between the client and the NAT pods.

Downtime will be caused by following flow.

1. create a new NAT client pod
2. CNI add is called and coild on the scheduled node configure the pod’s address and routes.
3. pod_watcher on NAT pod also configure a FoU link for new client but not configure the route.
4. finish the configuration on client side and start to send the traffic.
5. Traffic will be dropped because NAT pod doesn’t finish configuring yet!
6. NAT pod also finish configuring the route to client.

How

To minimize downtime, we change to set FoU link up just before adding a route.

Checklist

• Finish implementation of the issue
• Test all functions
• Have enough logs to trace activities
• Notify developers of necessary actions