fix(gateway-addons-helm): fix cluster variable in Grafana dashboard

[maxbrunet]

What type of PR is this?

What this PR does / why we need it:

The usage is label_values(<metric>, <label>), so I do not know if only passing the label works anywhere, but it does not work with Google's managed Prometheus.

This changes the query to extract the envoy_cluster_name values from the envoy_cluster_warming_state metric, which I believe, should be available for all configured clusters at all time.

Which issue(s) this PR fixes:

Fixes #

Release Notes: Yes/No

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 71.07%. Comparing base (ae449b6) to head (aa8589a).
⚠️ Report is 9 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6798   +/-   ##
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  Coverage   71.07%   71.07%           
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  Files         225      225           
  Lines       39810    39810           
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+ Hits        28293    28295    +2     
+ Misses       9852     9850    -2     
  Partials     1665     1665           

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[zirain]

the grafana doc said that only label is requried.

Deprecated, classic version of variable query editor. Enter a string with the query type using a syntax like the following: label_values(, )

is that a deprecated way?

[maxbrunet]

It could be a deprecated way, but even in that way it seems the metric is optional:

https://github.com/grafana/grafonnet/blob/5a8f3d6aa89b7e7513528371d2d1265aedc844bc/gen/grafonnet-v11.4.0/custom/dashboard/variable.libsonnet#L258-L261

I am not able to tell what the non-deprecated syntax would be as the JSON schema is not well documented.

Anyway, that does work for GMP, Google restricts some queries that could retrieve too much data like by requiring the metric name everywhere (another example is omitting the metric name in PromQL and using a regex on the __name__ meta label as selector, that's not possible with GMP). What I propose should work for GMP, vanilla Prometheus, and every other PromAPI-compatible backends

It is also consistent with other dashboard variables of the Envoy Gateway project:

gateway/charts/gateway-addons-helm/dashboards/envoy-proxy-global.json

Line 2935 in aee4b91

"query": "label_values(envoy_cluster_upstream_rq_time_bucket,namespace)",

[zirain]

To be clear, if GMP support label_values(label, metric), prefer to change all existing things to that way if possible

[maxbrunet]

Yes, this is the only outlier

[zirain]

Yes, this is the only outlier

Perhaps I misunderstood you, what I mean is that can you use label_values(label, metric) everywhere instead of label_values(metric, label)? will it work for GMP?

[maxbrunet]

label_values(label, metric) will not work anywhere, it is label_values(metric, label) or label_values(label)