k8s custom metric exporter json returned values - kubernetes

Question

I've tried to make a custom metric exporter for my kubernetes ..
And still failing to get the right value in order to exploit if within an hpa with this simplistic "a" variable ..
I don't really know how to export it according to different routes .. if I do {"a":"1"}, the error message on the hpa tells me it's missing kind .. then another fields ..
So I've did sum up the complete reproducible experiment below, in order to make it the simplest ever
Any Idea on how to complete this task ?
Thanks a lot for any clue, advice, enlightment, comment, notice
apiVersion: v1
kind: ConfigMap
metadata:
name: exporter
namespace: test
data:
os.php: |
<?php // If anyone knows a simple replacement other than swoole .. he's welcome --- Somehow I only think I'll need to know what the json output is expected for theses routes
$server = new Swoole\HTTP\Server("0.0.0.0",443,SWOOLE_PROCESS,SWOOLE_SOCK_TCP | SWOOLE_SSL);
$server->set(['worker_num' => 1,'ssl_cert_file' => __DIR__ . '/example.com+5.pem','ssl_key_file' => __DIR__ . '/example.com+5-key.pem']);
$server->on('Request', 'onMessage');
$server->start();
function onMessage($req, $res){
$value=1;
$url=$req->server['request_uri'];
file_put_contents('monolog.log',"\n".$url,8);//Log
if($url=='/'){
$res->end('{"status":"healthy"}');return;
} elseif($url=='/metrics'){
$res->end('a '.$value);return;
} elseif($url=='/apis/custom.metrics.k8s.io/v1beta1'){ // <-- This url is called lots of time in the logs
$res->end('{"kind": "APIResourceList","apiVersion": "v1","groupVersion": "custom.metrics.k8s.io/v1beta1","resources": [{"name": "namespaces/a","singularName": "","namespaced": false,"kind": "MetricValueList","verbs": ["get"]}]}');return;
} elseif($url=='/apis/custom.metrics.k8s.io/v1beta1/namespaces/test/services/test-metrics-exporter/a'){
$res->end('{"kind": "MetricValueList","apiVersion": "custom.metrics.k8s.io/v1beta1","metadata": {"selfLink": "/apis/custom.metrics.k8s.io/v1beta1/namespaces/test/services/test-metrics-exporter-svc/a"},"items": [{"describedObject": {"kind": "Service","namespace": "test","name": "test-metrics-exporter-svc","apiVersion": "/v1"},"metricName": "a","timestamp": "2020-06-21T08:35:58Z","value": "'.$value.'","selector": null}]}');return;
}
$res->status(404);return;
}
---
apiVersion: v1
kind: Service
metadata:
name: test-metrics-exporter
namespace: test
annotations:
prometheus.io/port: '443'
prometheus.io/scrape: 'true'
spec:
ports:
- port: 443
protocol: TCP
selector:
app: test-metrics-exporter
---
apiVersion: apps/v1
kind: Deployment
metadata:
name: test-metrics-exporter
namespace: test
spec:
selector:
matchLabels:
app: test-metrics-exporter
template:
metadata:
labels:
app: test-metrics-exporter
spec:
terminationGracePeriodSeconds: 1
volumes:
- name: exporter
configMap:
name: exporter
defaultMode: 0744
items:
- key: os.php
path: os.php
containers:
- name: test-metrics-exporter
image: openswoole/swoole:latest
imagePullPolicy: IfNotPresent
volumeMounts:
- name: exporter
mountPath: /var/www/os.php
subPath: os.php
command:
- /bin/sh
- -c
- |
touch monolog.log;
apt update && apt install wget -y && wget https://github.com/FiloSottile/mkcert/releases/download/v1.4.3/mkcert-v1.4.3-linux-amd64
cp mkcert-v1.4.3-linux-amd64 /usr/local/bin/mkcert && chmod +x /usr/local/bin/mkcert
mkcert example.com "*.example.com" example.test localhost 127.0.0.1 ::1
php os.php &
tail -f monolog.log
---
apiVersion: apps/v1
kind: Deployment
metadata:
name: alpine
namespace: test
spec:
selector:
matchLabels:
app: alpine
template:
metadata:
labels:
app: alpine
spec:
terminationGracePeriodSeconds: 1
containers:
- name: alpine
image: alpine
imagePullPolicy: IfNotPresent
command:
- /bin/sh
- -c
- |
tail -f /dev/null
---
kind: HorizontalPodAutoscaler
apiVersion: autoscaling/v2beta1
metadata:
name: alpine
namespace: test
spec:
scaleTargetRef:
kind: Deployment
name: alpine
apiVersion: apps/v1
minReplicas: 1
maxReplicas: 10
metrics:
- type: Object
object:
target:
kind: Service
name: test-metrics-exporter
metricName: a
targetValue: '1'
---
# This is the Api hook for custom metrics
apiVersion: apiregistration.k8s.io/v1beta1
kind: APIService
metadata:
name: v1beta1.custom.metrics.k8s.io
namespace: test
spec:
insecureSkipTLSVerify: true
group: custom.metrics.k8s.io
groupPriorityMinimum: 1000
versionPriority: 5
version: v1beta1
service:
name: test-metrics-exporter
namespace: test
port: 443