I have two deployments running a v1 and v2 of the same service in istio. I have set up a custom-metric 'istio-total-requests' to be collected through prometheus adapater.

I have set up an HPA to scale the v2 deployment and can see the target value increasing when I send requests, but what is not happening is the HPA is not scaling the number of pods/replicas.

I am running kubernetes v1.19 on minikube v1.13.1, and cannot understand why its not scaling.

prometheus:
  url: http://prometheus.istio-system.svc.cluster.local
rules:
  default: false
  custom:
# this rule matches cumulative cAdvisor metrics measured in seconds
  - seriesQuery: 'istio_requests_total{kubernetes_namespace!="",kubernetes_pod_name!=""}'
    seriesFilters: []      
    resources:
      # template: <<.Resource>>
      # skip specifying generic resource<->label mappings, and just
      # attach only pod and namespace resources by mapping label names to group-resources
      overrides:
        kubernetes_namespace: {resource: "namespace"}
        kubernetes_pod_name: {resource: "pod"}
    # specify that the `container_` and `_seconds_total` suffixes should be removed.
    # this also introduces an implicit filter on metric family names
    name:
      # we use the value of the capture group implicitly as the API name
      # we could also explicitly write `as: "$1"`
      matches: "^(.*)_total"
      as: "${1}_per_second"
      # matches: ""
      # as: ""
    # specify how to construct a query to fetch samples for a given series
    # This is a Go template where the `.Series` and `.LabelMatchers` string values
    # are available, and the delimiters are `<<` and `>>` to avoid conflicts with
    # the prometheus query language
    metricsQuery: "sum(rate(<<.Series>>{<<.LabelMatchers>>}[1m])) by (<<.GroupBy>>)"

HPA YAML

apiVersion: autoscaling/v2beta2
kind: HorizontalPodAutoscaler
metadata:
  name: translate-deployment-v2-hpa
spec:
  minReplicas: 1
  maxReplicas: 10
  metrics:
  - type: Pods
    pods:
      metric:
        name: istio_requests_per_second
        # selector: {matchLabels: {destination_version: 0.0.2}}
      target:
        type: AverageValue
        averageValue: 10
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: translate-deployment-v2      

See the HPA pulling and measuring the metric but not scaling, the window below it shows the prometheus-adapter getting queried for the metric successfully.

HPA Description

One final item which I'm not clear on, is what is the purpose of the selector in the hpa definition above ? Is it to select specific values from the data range which is queried by prometheus ?

For example I know the field I'm querying is output by default by envoy as follows:

istio_requests_total{app="istio-ingressgateway",chart="gateways",connection_security_policy="unknown",destination_app="translate-pod",destination_canonical_revision="0.0.1",destination_canonical_service="translate-pod",destination_principal="spiffe://cluster.local/ns/default/sa/default",destination_service="translate-service.default.svc.cluster.local",destination_service_name="translate-service",destination_service_namespace="default",destination_version="0.0.1",destination_workload="translate-deployment",destination_workload_namespace="default",heritage="Tiller",install_operator_istio_io_owning_resource="unknown",instance="172.17.0.5:15020",istio="ingressgateway",istio_io_rev="default",job="kubernetes-pods",kubernetes_namespace="istio-system",kubernetes_pod_name="istio-ingressgateway-6cfd75fc57-flmhp",operator_istio_io_component="IngressGateways",pod_template_hash="6cfd75fc57",release="istio",reporter="source",request_protocol="http",response_code="200",response_flags="-",service_istio_io_canonical_name="istio-ingressgateway",service_istio_io_canonical_revision="latest",source_app="istio-ingressgateway",source_canonical_revision="latest",source_canonical_service="istio-ingressgateway",source_principal="spiffe://cluster.local/ns/istio-system/sa/istio-ingressgateway-service-account",source_version="unknown",source_workload="istio-ingressgateway",source_workload_namespace="istio-system"}

Does the selector allow you to further filter the series data, if not what is the purpose and how do you use it ?