How to match the PrometheusRule to the AlertmanagerConfig with Prometheus Operator - kubernetes

Question

I have multiple prometheusRules(rule a, rule b), and each rule defined different exp to constraint the alert; then, I have different AlertmanagerConfig(one receiver is slack, then other one's receiver is opsgenie); How can we make a connection between rules and alertmanagerconfig? for example: if rule a is triggered, I want to send message to slack; if rule b is triggered, I want to send message to opsgenie.
Here is what I tried, however, that does not work. Did I miss something?
This is prometheuisRule file
apiVersion: monitoring.coreos.com/v1
kind: PrometheusRule
metadata:
labels:
prometheus: service-prometheus
role: alert-rules
app: kube-prometheus-stack
release: monitoring-prom
name: rule_a
namespace: monitoring
spec:
groups:
- name: rule_a_alert
rules:
- alert: usage_exceed
expr: salesforce_api_usage > 100000
labels:
severity: urgent
This is alertManagerConfig
apiVersion: monitoring.coreos.com/v1alpha1
kind: AlertmanagerConfig
metadata:
labels:
alertmanagerConfig: slack
name: slack
namespace: monitoring
resourceVersion: "25842935"
selfLink: /apis/monitoring.coreos.com/v1alpha1/namespaces/monitoring/alertmanagerconfigs/opsgenie-and-slack
uid: fbb74924-5186-4929-b363-8c056e401921
spec:
receivers:
- name: slack-receiver
slackConfigs:
- apiURL:
key: apiURL
name: slack-config
route:
groupBy:
- job
groupInterval: 60s
groupWait: 60s
receiver: slack-receiver
repeatInterval: 1m
routes:
- matchers:
- name: job
value: service_a
receiver: slack-receiver

Answer 1

You need to match on a label of the alert, in your case you're trying to match on the label job with the value service_a which doesn't exist. You could either match on a label that does exist in the prometheuisRule file, eg severity, by changing the match in the alertManagerConfig file:
route:
routes:
- match:
severity: urgent
receiver: slack-receiver
or you could add another label to the prometheuisRule file:
spec:
groups:
- name: rule_a_alert
rules:
- alert: usage_exceed
expr: salesforce_api_usage > 100000
labels:
severity: urgent
job: service_a