I have tried to deploy alertmanager service on a taint node by defining tolerations explicityl.

apiVersion: apps/v1
kind: Deployment
metadata:
  name: alertmanager
  namespace: monitoring
spec:
  replicas: 1
  selector:
    matchLabels:
      app: alertmanager
  template:
    metadata:
      name: alertmanager
      labels:
        app: alertmanager
    spec:
      tolerations:
      - key: "prometheusnew"
        operator: "Equal"
        value: "false"
        effect: "NoExecute"
      affinity:
        nodeAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
            nodeSelectorTerms:
            - matchExpressions:
              - key: placement_affinity
                operator: In
                values:
                - prometheusnew
      containers:
      - name: alertmanager
        image: prom/alertmanager:v0.15.3
        args:
          - '--config.file=/etc/alertmanager/config.yml'
          - '--storage.path=/alertmanager'
        ports:
        - name: alertmanager
          containerPort: 9093
        volumeMounts:
        - name: config-volume
          mountPath: /etc/alertmanager
        - name: alertmanager
          mountPath: /alertmanager
      volumes:
      - name: config-volume
        configMap:
          name: alertmanager
      - name: alertmanager
        emptyDir: {}

The cluster ip 172.30.148.104 is accessible from the same node but the pods and service ip is not accessible from any other nodes or pods in different node.

NAME           TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)    AGE
alertmanager   ClusterIP   172.30.148.104   <none>        9093/TCP   20m

Pods are running fine and if deploy without taint tolerations it works fine. Appreciate any help, thanks.