# PrometheusNotConnectedToAlertmanagers alert: what it means and how to fix it

What the PrometheusNotConnectedToAlertmanagers Prometheus alert means, its common causes, the PromQL rule and the runbook steps to fix it, with a ready-to-use rule in YAML.

Last reviewed 2026-10-31

Prometheus has discovered no Alertmanager to send alerts to. Rules are still evaluated and alerts still show as firing on the Prometheus `/alerts` page, but no notifications go out. Everything is silent and nothing looks wrong, which is why this alert should be routed through a channel that does not depend on the same Alertmanager.

* **Severity**: Warning (`warning`)
* **Fires after**: 10m
* Part of the [Prometheus alert rules](https://n9e.github.io/alert-rules/prometheus.md) (`prometheus.yml`)

## The rule[​](#the-rule "Direct link to The rule")

```
# Without max_over_time, failed scrapes could create false negatives, see

# https://www.robustperception.io/alerting-on-gauges-in-prometheus-2-0 for details.

max_over_time(prometheus_notifications_alertmanagers_discovered{job="prometheus-k8s",namespace="monitoring"}[5m]) < 1
```

Alert message: `Prometheus {{$labels.namespace}}/{{$labels.pod}} is not connected to any Alertmanagers.`

## Common causes[​](#common-causes "Direct link to Common causes")

* The `alerting` section of the configuration is missing or was removed.
* Alertmanager discovery returns nothing: wrong service name, namespace or port name. With the Operator, check `spec.alerting.alertmanagers` in the Prometheus resource.
* Prometheus lacks RBAC permissions to list the endpoints of the Alertmanager service.
* All Alertmanager Pods are down, so the service has no endpoints.

## How to fix it[​](#how-to-fix-it "Direct link to How to fix it")

1. Check whether the Alertmanager instances are healthy and reachable;
2. Confirm Alertmanager discovery on the Prometheus /status page;
3. If the queue is full, check whether Alertmanager processing is stuck or the alert volume spiked abnormally;
4. After recovery, confirm Alertmanager actually received the alerts so nothing fails silently.

## Notes[​](#notes "Direct link to Notes")

* The Prometheus `/status` page (Runtime & Build Information) lists the Alertmanagers it has discovered.
* The expression selects `job="prometheus-k8s"`, `namespace="monitoring"`. If your scrape job or namespace is named differently, change these matchers or the rule never matches.

## Metrics it uses[​](#metrics-it-uses "Direct link to Metrics it uses")

* `prometheus_notifications_alertmanagers_discovered` (Prometheus's own metrics)

## Related alerts[​](#related-alerts "Direct link to Related alerts")

* [PrometheusErrorSendingAlertsToAnyAlertmanager](https://n9e.github.io/alert-rules/prometheus.md#prometheuserrorsendingalertstoanyalertmanager): …% minimum errors while sending alerts from Prometheus …/… to any Alertmanager.
* [PrometheusErrorSendingAlertsToSomeAlertmanagers](https://n9e.github.io/alert-rules/prometheus.md#prometheuserrorsendingalertstosomealertmanagers): …% errors while sending alerts from Prometheus …/… to Alertmanager ….
* [PrometheusNotificationQueueRunningFull](https://n9e.github.io/alert-rules/prometheus.md#prometheusnotificationqueuerunningfull): Alert notification queue of Prometheus …/… is running full.

## Prometheus rule YAML[​](#prometheus-rule-yaml "Direct link to Prometheus rule YAML")

Add this to a rules file loaded through `rule_files`, or download every Prometheus rule at once as [`prometheus.yml`](https://n9e.github.io/alert-rules/prometheus.yml).

```
- alert: PrometheusNotConnectedToAlertmanagers

  expr: |-

    # Without max_over_time, failed scrapes could create false negatives, see

    # https://www.robustperception.io/alerting-on-gauges-in-prometheus-2-0 for details.

    max_over_time(prometheus_notifications_alertmanagers_discovered{job="prometheus-k8s",namespace="monitoring"}[5m]) < 1

  for: 10m

  labels:

    severity: warning

  annotations:

    summary: "Prometheus {{$labels.namespace}}/{{$labels.pod}} is not connected to any Alertmanagers."

    runbook_url: "https://n9e.github.io/alert-rules/prometheus/prometheusnotconnectedtoalertmanagers"
```

**With Nightingale**: this rule ships in the [Kubernetes integration](https://n9e.github.io/integrations/kubernetes.md) template; [import it into a business group](https://n9e.github.io/docs/data/integrations/import.md) and Nightingale attaches the runbook to every alert it sends.

## Sources and license[​](#sources-and-license "Direct link to Sources and license")

The rule expression is adapted from [kube-prometheus](https://github.com/prometheus-operator/kube-prometheus) (Apache-2.0). The runbook steps come from [Nightingale's integration templates](https://github.com/ccfos/nightingale/tree/main/integrations) (Apache-2.0); the explanation and causes are written for this page.