Configurable sleep before nginx shutdown for upstream LB

[yvespp]

Is this a BUG REPORT or FEATURE REQUEST? (choose one): FEATURE REQUEST
NGINX Ingress controller version: 0.26.1
Kubernetes version (use kubectl version): 1.15.5
Environment: on prem

Followup of: #4006 (comment)

We are on prem and use F5 as a TCP loadbalancer in front of the nginx pods:
client -> F5 TCP LB -> nginx Pods

The F5 checks the nginx health check every 5 seconds.
A nginx pod starts to terminate and immediately stops accepting new connections.
The F5 still sends new connections to the nginx pod for 5 seconds because the health check did not fail yet.
I think what would help here is a configurable sleep in the wait-shutdown hook between the stop of the controller (which fails the health check) and the shutdown of nginx. Ningx would still acception new connections until the F5 has realized that it is down and stops sending new connections to it.

[Cittarasu]

@aledbf @yvespp -- We will never be able to synchronize external LB health check to Nginx termination initiation in the wait-shutdown hook? Configurable sleep doesn't sync with external health check interval though even it's configured to match the health check interval in LB and sleep in the wait-shutdown hook?

[yvespp]

@Cittarasu the sleeps gives the external LB time to notice that the Nginx Ingress is shutting down and stops sending new connections to that backend. You have to make sure that the sleep is long enough for that.

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