Is it possible to set the name of an external metric for a HorizontalPodAutoscaler from a configmap? GKE - kubernetes

Question

I am modifying a deployment which autoscales using a HorizontalPodAutoscaler (HPA). This deployment is part of a pipeline in which workers read messages from pubsub subscriptions, do some work and publish to the next topic. Right now I use a configmap to define the pipeline for the deployments (the configmap contains input subscription and output topics). The HPA autoscales based on the number of messages on the input subscription. I would like to be able to pull the subscription name for the HPA from a configmap if possible? Is there a way to do this?
example HPA:
apiVersion: autoscaling/v2beta1
kind: HorizontalPodAutoscaler
metadata:
name: my-deployment-hpa
namespace: default
labels:
name: my-deployment-hpa
spec:
minReplicas: 1
maxReplicas: 10
metrics:
- external:
metricName: pubsub.googleapis.com|subscription|num_undelivered_messages
metricSelector:
matchLabels:
resource.labels.subscription_id: "$INPUT_SUBSCRIPTION"
targetAverageValue: "2"
type: External
scaleTargetRef:
apiVersion: apps/v1
kind: Deployment
name: my-deployment
The value from the HPA currently $INPUT_SUBSCRIPTION could ideally come from a configmap.

Answer 1

Posting this answer as a community wiki for a better visibility as well as the answer was provided in the comments.
Answering the question from the post:
I would like to be able to pull the subscription name for the HPA from a configmap if possible? Is there a way to do this?
As pointed by user #Abdennour TOUMI there is no possibility to set the metric used by HPA with a ConfigMap:
Unfortunately, you cannot.. but you can using prometheus-adapter + HPA . Check this tuto: itnext.io/...
As for a manual workaround you could use a script that will extract needed metric name from the configMap and use a template to replace and apply new HPA.
With a configMap like:
apiVersion: v1
kind: ConfigMap
metadata:
name: example
data:
metric_name: "new_awesome_metric" # <-
not_needed: "only for example"
And following script:
#!/bin/bash
# variables
hpa_file_name="hpa.yaml"
configmap_name="example"
string_to_replace="PLACEHOLDER"
# extract the metric name used in a configmap
new_metric=$(kubectl get configmap $configmap_name -o json | jq '.data.metric_name')
# use the template to replace the $string_to_replace with your $new_metric and apply it
sed "s/$string_to_replace/$new_metric/g" $hpa_file_name | kubectl apply -f -
This script will need to have a hpa.yaml with the template to apply it as resource (example from question could be used with a change:
resource.labels.subscription_id: PLACEHOLDER
For more reference this HPA definition could be based on this guide:
Cloud.google.com: Kubernetes Engine: Tutorials: Autoscaling-metrics: PubSub