1. First, you need to create an EKS cluster. You can use the AWS Management Console, AWS CLI, or any other preferred method to create the cluster.
2. Once the cluster is created, you need to install Prometheus on it. Alertmanager is a part of the Prometheus ecosystem and requires Prometheus to be installed to function properly. You can follow the instructions in the Prometheus documentation to install Prometheus on EKS.
3. After installing Prometheus, you need to create a Kubernetes deployment for Alertmanager. You can use the following YAML file as a template:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: alertmanager
spec:
  replicas: 1
  selector:
    matchLabels:
      app: alertmanager
  template:
    metadata:
      labels:
        app: alertmanager
    spec:
      containers:
        - name: alertmanager
          image: prom/alertmanager
          args:
            - "--config.file=/etc/alertmanager/config.yml"
          ports:
            - containerPort: 9093
          volumeMounts:
            - name: config
              mountPath: /etc/alertmanager
      volumes:
        - name: config
          configMap:
            name: alertmanager-config

This YAML file creates a Kubernetes deployment with one replica of the Alertmanager container, using the prom/alertmanager image. It also mounts a configuration file for Alertmanager, which is stored in a Kubernetes ConfigMap.

After creating the deployment YAML file, you need to create a ConfigMap with the Alertmanager configuration. You can use the following YAML file as a template:

apiVersion: v1
kind: ConfigMap
metadata:
name: alertmanager-config
data:
config.yml: |-
global:
slack_api_url:
route:
group_by: ['alertname']
group_wait: 30s
group_interval: 5m
repeat_interval: 12h
receiver: 'slack'
receivers:
- name: 'slack'
slack_configs:
- channel: '#alerts'
send_resolved: true
username: 'Alertmanager'

This YAML file creates a ConfigMap with the Alertmanager configuration. You need to replace <YOUR_SLACK_API_URL> it with the URL for your Slack webhook.

5. After creating the deployment and ConfigMap YAML files, you can deploy Alertmanager to your EKS cluster using the kubectl apply command:

kubectl apply -f alertmanager-deployment.yaml
kubectl apply -f alertmanager-configmap.yaml

After deploying Alertmanager, you can verify that it is running by checking the logs for the Alertmanager pod:

kubectl logs <alertmanager-pod-name>

You should see an output indicating that Alertmanager has started and is running.

7. Finally, you can configure Prometheus to use Alertmanager as a notification receiver. You can add the following section to your Prometheus configuration file:

alerting:
  alertmanagers:
  - static_configs:
    - targets:
      - alertmanager:9093

This configuration tells Prometheus to send alerts to Alertmanager at the address alertmanager:9093.

That’s it! You have now installed Alertmanager on your EKS cluster and configured Prometheus to send alerts to it.