[404-server] Conceal /metrics and /healthz behind port 10254

[jonpulsifer]

What this PR does / why we need it:

• Implements an HTTP multiplexer for the /metrics and /healthz endpoints and exposes a command line flag to change the port (default 10254)
• Implements a timeout (default 5s) for the graceful shutdown

Which issue this PR fixes:

Fixes #1733

Special notes for your reviewer:

This PR is getting pretty big.. I don't know if we should cut a release yet, or wait until we bump the manifests? code has been updated to maintain existing functionality, so i don't think i'm that worried anymore

The 404-server is supposed to be small, but it's getting bigger, I don't know what we want to do here

[jonpulsifer]

/assign @aledbf

[jonpulsifer]

I guess the real question is, does anyone use these metrics? This is supposed to just return http.StatusNotFound and the default backend - 404 string.

I don't know why but I just feel wrong feature creeping this thing

[aledbf]

I don't know why but I just feel wrong feature creeping this thing

I am not sure this adds real value for two reasons, just a counter for 404 is not very helpful and if you add the host being requested could produce an explosion of metrics.
Maybe this PR should be referenced as an example for those users that want this feature? (building a custom 404 image is easy). WDYT?

[ElvinEfendi]

IMO ingress-nginx should not be concerned about default backend service at all. By default we should not require --default-backend-service to be set and just return 404 from Nginx directly. And if a user wants to customize then they can deploy their custom default backend service and use --default-backend-service to configure it.

[aledbf]

By default we should not require --default-backend-service to be set and just return 404 from Nginx directly.

We cannot break this rule.

[ElvinEfendi]

We cannot break this rule.

@aledbf can you elaborate? Are you worried that it will introduce snowflake in controller.go logic?

[jonpulsifer]

Maybe this PR should be referenced as an example for those users that want this feature? (building a custom 404 image is easy). WDYT?

I'm totally comfortable with that, I kinda just want to 🔥 the metrics endpoint altogether? I'm okay with /healthz being public from a security perspective

[ElvinEfendi]

I sketched something quickly for the idea I suggest at #3125 (comment), it is simpler than I guessed: https://github.com/kubernetes/ingress-nginx/pull/3126/files

[aledbf]

I'm totally comfortable with that, I kinda just want to fire the metrics endpoint altogether?

Not sure about that because someone could be using what's being exposed right now.

[aledbf]

Closing

[ElvinEfendi]

@aledbf what's the problem with this PR? It is making things better without breaking anything, no? After #3126 gets merged https://github.com/kubernetes/ingress-nginx/tree/master/images/404-server will serve just as an example, and I don't see any issue with making that example custom 404 page more secure and configurable.

[aledbf]

@ElvinEfendi this introduce the same issue than here #3116 (comment) but for all 404 handled by the default backend

[aledbf]

Also, the 404-server image is not used only by ingress-nginx

[jonpulsifer]

the 404-server aka k8s.gcr.io/defaultbackend is also the backend used by the https://github.com/kubernetes/ingress-gce on GKE, you can find it in the kube-system namespace as deploy/l7-default-backend

[jonpulsifer]

/reopen

[k8s-ci-robot]

@jonpulsifer: Reopening this PR.

In response to this:

/reopen

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[k8s-ci-robot]

@jonpulsifer: failed to re-open PR: state cannot be changed. The change-default-backend-metrics-port branch has been deleted.

In response to this:

/reopen

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[jonpulsifer]

/reopen

[k8s-ci-robot]

@jonpulsifer: Reopening this PR.

In response to this:

/reopen

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[aledbf]

/lgtm
/approve

[aledbf]

/hold

[aledbf]

@bowei @nicksardo ping

[jonpulsifer]

commits have been squashed, ready to go I think 😄

also super thanks for the incorporated adjustments to the code (retaining functionality on :8080/healthz and the rest of the golang stuff)

[bowei]

/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf, bowei, jonpulsifer

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[aledbf]

@bowei can you help with the publication of the image to gcr?

[bowei]

ahhhh ok, doing it

[NicoleG25]

It appears that CVE-2018-1002104 was assigned to this issue.