Unable to retrieve custom metrics from prometheus-adapter - kubernetes

Question

i am trying to experiment with scaling one of my application pods running on my raspberry pi kubernetes cluster using HPA + custom metrics but ran into several issues which despite reading the documentations on https://github.com/DirectXMan12/k8s-prometheus-adapter and troubleshooting for the past 2 days, i am still having difficulties grasping why some problems are happening.
Firstly, i built an ARM-compatible image of k8s-prometheus-adapter and install it using helm. I can confirm its running properly by checking the pod logs.
I have also set up a script which sends raspberry pis temperature to pushgateway and i can query via this Prometheus query node_temp, which will return the following series
node_temp{job="kube4"} 42
node_temp{job="kube1"} 44
node_temp{job="kube2"} 39
node_temp{job="kube3"} 40
Now i want to be able to scale one of my application pods using the above temperature values as an experiment to understand better how it works.
Below is my k8s-prometheus-adapter helm values.yml file
image:
repository: jaanhio/k8s-prometheus-adapter-arm
tag: latest
logLevel: 7
prometheus:
url: http://10.17.0.12
rules:
default: false
custom:
- seriesQuery: 'etcd_object_counts'
resources:
template: <<.Resource>>
name:
as: "etcd_object"
metricsQuery: count(etcd_object_counts)
- seriesQuery: 'node_temp'
resources:
template: <<.Resource>>
name:
as: "node_temp"
metricsQuery: count(node_temp)
After installing via helm, i ran kubectl get apiservices and can see v1beta1.custom.metrics.k8s.io listed.
i then ran kubectl get --raw /apis/custom.metrics.k8s.io/v1beta1 | jq and got the following
{
"kind": "APIResourceList",
"apiVersion": "v1",
"groupVersion": "custom.metrics.k8s.io/v1beta1",
"resources": [
{
"name": "jobs.batch/node_temp",
"singularName": "",
"namespaced": true,
"kind": "MetricValueList",
"verbs": [
"get"
]
},
{
"name": "jobs.batch/etcd_object",
"singularName": "",
"namespaced": true,
"kind": "MetricValueList",
"verbs": [
"get"
]
},
]
i then tried to query the value of the registered node_temp metrics using kubectl get --raw /apis/custom.metrics.k8s.io/v1beta1/jobs/*/node_temp but got the following response
Error from server (InternalError): Internal error occurred: unable to list matching resources
Questions:
Why is the node_temp metrics associated with jobs.batch resource type?
Why am i not able to retrieve the value of metrics via kubectl get --raw /apis/custom.metrics.k8s.io/v1beta1/jobs/*/node_temp?
What is a definitive way of figuring the path of the query? e.g /apis/custom.metrics.k8s.io/v1beta1/jobs/*/node_temp i kinda trial and error until i got see somewhat of a response. i also see some other path with namespaces in the query e.g /apis/custom.metrics.k8s.io/v1beta1/namespaces/*/metrics/foo_metrics
Any help and advice will be greatly appreciate!

Answer 1

Why is the node_temp metrics associated with jobs.batch resource type?
It picks the labels attached to the prometheus metrics and tries to interpret them, in this case u have clearely "job-kube4"
Why am i not able to retrieve the value of metrics via kubectl get --raw /apis/custom.metrics.k8s.io/v1beta1/jobs/*/node_temp?
Metrics are namespaced, see the "namespaced:true" so you'll need "/apis/custom.metrics.k8s.io/v1beta1/namespaces//jobs//node_temp"
What is a definitive way of figuring the path of the query? e.g /apis/custom.metrics.k8s.io/v1beta1/jobs//node_temp i kinda trial and error until i got see somewhat of a response. i also see some other path with namespaces in the query e.g /apis/custom.metrics.k8s.io/v1beta1/namespaces//metrics/foo_metrics
Check https://github.com/kubernetes/community/blob/master/contributors/design-proposals/instrumentation/custom-metrics-api.md#api-paths