Outdated description about service-upstream?

[awx-fuyuanchu]

NGINX Ingress controller version (exec into the pod and run nginx-ingress-controller --version.): v0.41.2

Kubernetes version (use kubectl version):

Client Version: version.Info{Major:"1", Minor:"21", GitVersion:"v1.21.2", GitCommit:"092fbfbf53427de67cac1e9fa54aaa09a28371d7", GitTreeState:"clean", BuildDate:"2021-06-16T12:59:11Z", GoVersion:"go1.16.5", Compiler:"gc", Platform:"darwin/amd64"}
Server Version: version.Info{Major:"1", Minor:"19+", GitVersion:"v1.19.13-gke.1900", GitCommit:"ee714a7b695ca42b9bd0c8fe2c0159024cdcba5e", GitTreeState:"clean", BuildDate:"2021-08-11T09:19:42Z", GoVersion:"go1.15.13b5", Compiler:"gc", Platform:"linux/amd64"}
WARNING: version difference between client (1.21) and server (1.19) exceeds the supported minor version skew of +/-1

Environment:

• Cloud provider or hardware configuration: GKE
• OS (e.g. from /etc/os-release): COS
• Kernel (e.g. uname -a): Linux gitlab 5.4.129+ Basic structure  #1 SMP Mon Jul 26 19:50:53 PDT 2021 x86_64 Intel(R) Xeon(R) CPU @ 2.80GHz GenuineIntel GNU/Linux
• Install tools:
  • Please mention how/where was clsuter created like kubeadm/kops/minikube/kind etc.
• Basic cluster related info:
  • kubectl version
  • kubectl get nodes -o wide

What happened:

The description about service-upstream in doc https://github.com/kubernetes/ingress-nginx/blob/main/docs/user-guide/nginx-configuration/annotations.md#service-upstream

This can be desirable for things like zero-downtime deployments as it reduces the need to reload NGINX configuration when Pods come up and down. 

But I think there is no need to reload NGINX configuration when Pods come up and down since dynamic backend configuration are enabled by default. The description maybe need an update.

What you expected to happen:

/kind bug

Many thanks for your great works.

[k8s-ci-robot]

@FuyuanChu: This issue is currently awaiting triage.

If Ingress contributors determines this is a relevant issue, they will accept it by applying the triage/accepted label and provide further guidance.

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[longwuyuan]

/remove-king bug
/kind documentation
/area docs

[longwuyuan]

/remove-kind bug

[kundan2707]

/assign