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 1m58s on platformidentification.JobType{Release:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 1m58s, firing for 0s:
Apr 27 11:50:21.884 - 118s  I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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 2m28s on platformidentification.JobType{Release:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 2m28s, firing for 0s:
Apr 26 13:17:50.114 - 148s  I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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 58s on platformidentification.JobType{Release:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 58s, firing for 0s:
Apr 26 00:16:48.243 - 58s   I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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 2m28s on platformidentification.JobType{Release:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 2m28s, firing for 0s:
Apr 25 18:55:33.101 - 148s  I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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 1m28s on platformidentification.JobType{Release:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 1m28s, firing for 0s:
Apr 24 16:37:03.822 - 88s   I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 28s, firing for 0s:
Apr 24 00:06:20.140 - 28s   I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 2m58s, firing for 0s:
Apr 23 10:47:25.981 - 178s  I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 28s, firing for 0s:
Apr 24 08:30:57.177 - 28s   I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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 58s on platformidentification.JobType{Release:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 58s, firing for 0s:
Apr 22 16:24:15.508 - 58s   I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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 4m56s on platformidentification.JobType{Release:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 4m56s, firing for 0s:
Apr 22 11:46:06.120 - 268s  I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}
Apr 22 11:51:06.120 - 28s   I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 3m58s, firing for 0s:
Apr 23 02:59:19.227 - 238s  I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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 58s on platformidentification.JobType{Release:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 58s, firing for 0s:
Apr 21 10:36:13.529 - 58s   I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 1m58s, firing for 0s:
Apr 20 15:05:22.481 - 118s  I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 3m28s, firing for 0s:
Apr 20 10:28:03.069 - 208s  I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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 6m58s on platformidentification.JobType{Release:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 6m58s, firing for 0s:
Apr 19 12:59:59.233 - 418s  I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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 1m28s on platformidentification.JobType{Release:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 1m28s, firing for 0s:
Apr 19 05:20:52.265 - 88s   I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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 1m28s on platformidentification.JobType{Release:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 1m28s, firing for 0s:
Apr 18 22:19:08.266 - 88s   I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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 56s on platformidentification.JobType{Release:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 56s, firing for 0s:
Apr 18 13:59:42.934 - 28s   I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}
Apr 18 14:01:12.934 - 28s   I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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 2m28s on platformidentification.JobType{Release:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 2m28s, firing for 0s:
Apr 18 09:38:39.652 - 148s  I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 28s, firing for 0s:
Apr 17 06:03:43.620 - 28s   I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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 4m26s on platformidentification.JobType{Release:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 4m26s, firing for 0s:
Apr 18 04:21:13.684 - 30s   I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}
Apr 18 04:22:15.684 - 208s  I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}
Apr 18 04:22:45.684 - 28s   I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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 1m28s on platformidentification.JobType{Release:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 1m28s, firing for 0s:
Apr 15 11:06:00.285 - 88s   I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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 58s on platformidentification.JobType{Release:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 58s, firing for 0s:
Apr 16 04:10:21.346 - 58s   I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver 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:"4.14", FromRelease:"", Platform:"vsphere", Architecture:"amd64", Network:"ovn", Topology:"ha"} (maxAllowed=0s): pending for 2m58s, firing for 0s:
Apr 15 05:27:46.931 - 178s  I alert/KubeAPIErrorBudgetBurn namespace/openshift-kube-apiserver ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}