Hpa not fetching existing custom metric? - kubernetes

Question

I'm using mongodb-exporter for store/query the metrics via prometheus. I have set up a custom metric server and storing values for that .
That is the evidence of prometheus-exporter and custom-metric-server works compatible .
Query:
kubectl get --raw "/apis/custom.metrics.k8s.io/v1beta1/namespaces/monitoring/pods/*/mongodb_mongod_wiredtiger_cache_bytes"
Result:
{"kind":"MetricValueList","apiVersion":"custom.metrics.k8s.io/v1beta1","metadata":{"selfLink":"/apis/custom.metrics.k8s.io/v1beta1/namespaces/monitoring/pods/%2A/mongodb_mongod_wiredtiger_cache_bytes"},"items":[{"describedObject":{"kind":"Pod","namespace":"monitoring","name":"mongo-exporter-2-prometheus-mongodb-exporter-68f95fd65d-dvptr","apiVersion":"/v1"},"metricName":"mongodb_mongod_wiredtiger_cache_bytes","timestamp":"TTTTT","value":"0"}]}
In my case when I create a hpa for this custom metrics from mongo exporter, hpa return this error to me :
failed to get mongodb_mongod_wiredtiger_cache_bytes utilization: unable to get metrics for resource mongodb_mongod_wiredtiger_cache_bytes: no metrics returned from resource metrics API
What is the main issue on my case ? I have checked all configs and flow is looking fine, but where is the my mistake .
Help
Thanks :)

Answer 1

In comments you wrote that you have enabled external.metrics, however in original question you had issues with custom.metrics
In short:
metrics supports only basic metric like CPU or Memory.
custom.metrics allows you to extend basic metrics to all Kubernetes objects (http_requests, number of pods, etc.).
external.metrics allows to gather metrics which are not Kubernetes objects:
External metrics allow you to autoscale your cluster based on any
metric available in your monitoring system. Just provide a metric
block with a name and selector, as above, and use the External metric
type instead of Object
For more detailed description, please check this doc.
Minikube
To verify if custom.metrics are enabled you need to execute command below and check if you can see any metrics-server... pod.
$ kubectl get pods -n kube-system
...
metrics-server-587f876775-9qrtc 1/1 Running 4 5d1h
Second way is to check if minikube have enabled metrics-server by
$ minikube addons list
...
- metrics-server: enabled
If it is disabled just execute
$ sudo minikube addons enable metrics-server
✅ metrics-server was successfully enabled
GKE
Currently at GKE heapster and metrics-server are turn on as default but custom.metrics are not supported by default.
You have to install prometheus adapter or stackdriver.
Kubeadm
Kubeadm do not include heapster or metrics server at the beginning. For easy installation, you can use this YAML.
Later you have to install prometheus adapter.
Apply custom.metrics
It's the same for Minikube, Kubeadm, GKE.
Easiest way to apply custom.metrics is to install prometheus adapter via Helm.
After helm installation you will be able to see note:
NOTES:
my-release-prometheus-adapter has been deployed.
In a few minutes you should be able to list metrics using the following command(s):
kubectl get --raw /apis/custom.metrics.k8s.io/v1beta1
As additional information, you can use jq to get more user friendly output.
kubectl get --raw /apis/custom.metrics.k8s.io/v1beta1 | jq .