proposal: application health check

[mqliang]

It's useful to provide backend health check functionality, it could be implemented by integrating ngx_http_healthcheck_module

[euank]

@mqliang that repo itself states that it's deprecated in favour of https://github.com/yaoweibin/nginx_upstream_check_module, so such an implementation should probably use different nginx features.

By default though, the controller will remove backends that have failed the kubernetes defined healthchecks, so you can already define kubernetes healthchecks for your pod and have some functionality there.

See this doc for what exists now: https://github.com/kubernetes/ingress/blob/5cdb8fe4fb3d0d4bc4430a09726810b5daddb949/controllers/nginx/configuration.md#custom-nginx-upstream-checks

What feature do you specifically want and what usecase which isn't already covered by k8s healthchecks?

[chrismoos]

I did this PR when ingress was getting moved over here:

kubernetes-retired/contrib#2072

I'll try to get it rebased over here.

[aledbf]

Closing. Please use the readiness and liveness probes provided by Kubernetes.