IMPORTANT NOTE: This site is not official Red Hat documentation and is provided for informational purposes only. These guides may be experimental, proof of concept, or early adoption. Officially supported documentation is available at docs.openshift.com and access.redhat.com.

Custom AlertManager in ROSA 4.9.x

ROSA 4.9.x introduces a new way to provide custom AlertManager configuration to receive alerts from User Workload Management.

The OpenShift Administrator can use the Prometheus Operator to create a custom AlertManager resource and then use the AlertManagerConfig resource to configure User Workload Monitoring to use the custom AlertManager.

Prerequisites

AWS CLI
A Red Hat OpenShift for AWS (ROSA) cluster 4.9.0 or higher

Create Environment Variables

Before we get started we need to set some environment variables to be used throughout the guide.
```
export PROM_NAMESPACE=custom-alert-manager
```

Install Prometheus Operator

If you prefer you can do this from the Operator Hub in the cluster console itself.

Create a OperatorGroup and Subscription for the Prometheus Operator

cat << EOF | kubectl apply -f -
---
apiVersion: v1
kind: Namespace
metadata:
  name: ${PROM_NAMESPACE}
---
apiVersion: operators.coreos.com/v1
kind: OperatorGroup
metadata:
  name: federated-metrics
  namespace: ${PROM_NAMESPACE}
spec:
  targetNamespaces:
  - ${PROM_NAMESPACE}
---
apiVersion: operators.coreos.com/v1alpha1
kind: Subscription
metadata:
  name: prometheus
  namespace: ${PROM_NAMESPACE}
spec:
  channel: beta
  installPlanApproval: Automatic
  name: prometheus
  source: community-operators
  sourceNamespace: openshift-marketplace
EOF

Deploy AlertManager

Create an Alert Manager Configuration file

This will create a basic AlertManager configuration to send alerts to a slack channel. Configuring slack is outside the scope of this document. Update the variables to suit your slack integration.

   SLACK_API_URL=https://hooks.slack.com/services/XXX/XXX/XXX
   SLACK_CHANNEL='#paultest'
   cat << EOF | kubectl apply -n ${PROM_NAMESPACE} -f -
   apiVersion: v1
   kind: Secret
   metadata:
     name: custom-alertmanager
     namespace: ${PROM_NAMESPACE}
   stringData:
     alertmanager.yaml: |
       global:
         slack_api_url: "${SLACK_API_URL}"
       route:
         receiver: slack-notifications
         group_by: [alertname]
       receivers:
       - name: slack-notifications
         slack_configs:
         - channel: ${SLACK_CHANNEL}
           send_resolved: true
   ---
   apiVersion: monitoring.coreos.com/v1
   kind: Alertmanager
   metadata:
     name: custom-alertmanager
     namespace: ${PROM_NAMESPACE}
   spec:
     securityContext: {}
     replicas: 3
     configSecret: custom-alertmanager
   ---
   apiVersion: v1
   kind: Service
   metadata:
     name: custom-alertmanager
     namespace: ${PROM_NAMESPACE}
   spec:
     type: ClusterIP
     ports:
     - name: web
       port: 9093
       protocol: TCP
       targetPort: web
     selector:
       alertmanager: custom-alertmanager
   EOF

Configure User Workload Monitoring to use the custom AlertManager

Create an AlertManagerConfig for User Workload Monitoring

Note: This next command assumes the existing config.yaml in the user-workload-monitoring-config config map is empty. You should verify it with kubectl get -n openshift-user-workload-monitoring cm user-workload-monitoring-config -o yaml and simply edit in the differences if its not.

   cat << EOF | kubectl apply -f -
   apiVersion: v1
   kind: ConfigMap
   metadata:
     name: user-workload-monitoring-config
     namespace: openshift-user-workload-monitoring
   data:
     config.yaml: |
       thanosRuler:
         additionalAlertmanagerConfigs:
         - scheme: http
           pathPrefix: /
           timeout: "30s"
           apiVersion: v1
           staticConfigs: ["custom-alertmanager.$PROM_NAMESPACE.svc.cluster.   local:9093"]
   EOF

Create an Example Alert

Verify it works by creating a Prometheus Rule that will fire off an alert

cat << EOF | kubectl apply -n $PROM_NAMESPACE -f -
apiVersion: monitoring.coreos.com/v1
kind: PrometheusRule
metadata:
  name: prometheus-example-rules
  namespace: ${PROM_NAMESPACE}
spec:
  groups:
  - name: example.rules
    rules:
    - alert: ExampleAlert
      expr: vector(1)
EOF

Forward a port to the alert manager service

 kubectl port-forward -n ${PROM_NAMESPACE} svc/custom-alertmanager 9093:9093

Browse to http://localhost:9093/#/alerts to see the alert “ExampleAlert”
Check the Alert was sent to Slack