We have many guards making sure that there are always at least two instances of the kube-apiserver. If we ever reach a single kube-apiserver and it causes disruption for the clients, other alerts such as KubeAPIErrorBudgetBurn will fire.
KubeAPIDown is here to make sure that Prometheus and really any client can reach the kube-apiserver, which they can even when there is only one instance of kube-apiserver running. If they can't or that availability is disrupted, `KubeAPIErrorBudgetBurn` will fire.
Comment 23058588 by Marcel Härri at 2023-09-19T06:57:07.949+0000

Mar 12 18:52:24.937 - 58s E namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/firing severity/critical ALERTS
{alertname="KubeAPIErrorBudgetBurn", alertstate="firing", long="1h", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="critical", short="5m"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 7m28s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 7m28s, firing for 0s:
May 14 18:20:57.263 - 448s  I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 28s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 28s, firing for 0s:
May 13 06:40:36.183 - 28s   I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 13m46s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 13m46s, firing for 0s:
May 14 12:32:10.232 - 826s  I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 28s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 28s, firing for 0s:
May 13 11:46:18.654 - 28s   I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 3m58s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 3m58s, firing for 0s:
May 12 21:45:30.879 - 238s  I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 28s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 28s, firing for 0s:
May 13 02:24:34.108 - 28s   I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 2m58s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 2m58s, firing for 0s:
May 12 14:51:50.495 - 178s  I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 28s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 28s, firing for 0s:
May 12 05:10:47.720 - 28s   I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 23m12s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 23m12s, firing for 0s:
May 12 10:31:19.174 - 230s  I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="1d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="2h"}
May 12 10:31:19.174 - 1162s I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 5m56s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 5m56s, firing for 0s:
May 08 23:29:49.282 - 28s   I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="1d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="2h"}
May 08 23:29:49.282 - 328s  I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 1m58s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 1m58s, firing for 0s:
May 08 18:03:45.567 - 118s  I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 3m58s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 3m58s, firing for 0s:
May 08 01:57:11.076 - 238s  I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 8m0s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 8m0s, firing for 0s:
May 11 17:48:47.814 - 452s  I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}
May 11 17:57:51.814 - 28s   I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 4m58s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 4m58s, firing for 0s:
May 07 13:57:53.544 - 298s  I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 28s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 28s, firing for 0s:
May 06 13:50:14.685 - 28s   I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 3m26s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 3m26s, firing for 0s:
May 06 19:33:49.960 - 148s  I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}
May 06 19:36:49.960 - 58s   I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 15m50s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 15m50s, firing for 0s:
May 06 06:11:55.670 - 922s  I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}
May 06 06:13:49.670 - 28s   I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="1d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="2h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 17m10s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 17m10s, firing for 0s:
May 06 00:42:56.202 - 42s   I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}
May 06 00:44:10.202 - 988s  I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 28s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 28s, firing for 0s:
May 05 18:55:10.559 - 28s   I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 4m28s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 4m28s, firing for 0s:
May 04 23:07:57.435 - 268s  I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 3m28s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 3m28s, firing for 0s:
May 05 11:29:24.093 - 208s  I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 4m28s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 4m28s, firing for 0s:
May 03 23:39:56.458 - 268s  I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 22m32s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 22m32s, firing for 0s:
May 03 16:23:50.824 - 172s  I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="1d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="2h"}
May 03 16:23:50.824 - 1180s I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 28s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 28s, firing for 0s:
May 02 20:59:47.476 - 28s   I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 5m58s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 5m58s, firing for 0s:
May 02 08:09:08.894 - 358s  I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 2m58s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 2m58s, firing for 0s:
May 02 01:19:19.975 - 178s  I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 5m58s on platformidentification.JobType{Release:"4.16", FromRelease:"", Platform:"azure", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 5m58s, firing for 0s:
Apr 30 22:12:59.888 - 358s  I namespace/openshift-kube-apiserver alert/KubeAPIErrorBudgetBurn alertstate/pending severity/warning ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}