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"}

Found files: [/logs/artifacts/junit/test-failures-summary_20240426-123514.json]
response Body: {"ProwJobName":"periodic-ci-openshift-multiarch-master-nightly-4.12-ocp-e2e-aws-ovn-arm64-techpreview-serial","ProwJobRunID":1783825316989374464,"Release":"4.12","CompareRelease":"4.12","Tests":[{"Name":"[bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above info","Risk":{"Level":{"Name":"High","Level":100},"Reasons":["This test has passed 100.00% of 24 runs on jobs ['periodic-ci-openshift-multiarch-master-nightly-4.12-ocp-e2e-aws-ovn-arm64-techpreview-serial'] in the last 14 days."]},"OpenBugs":[]}],"OverallRisk":{"Level":{"Name":"High","Level":100},"Reasons":["Maximum failed test risk: High"]},"OpenBugs":[]}

Found files: [/logs/artifacts/junit/test-failures-summary_20240426-123514.json]
response Body: {"ProwJobName":"periodic-ci-openshift-multiarch-master-nightly-4.12-ocp-e2e-aws-ovn-arm64-techpreview-serial","ProwJobRunID":1783825316989374464,"Release":"4.12","CompareRelease":"4.12","Tests":[{"Name":"[bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above info","Risk":{"Level":{"Name":"High","Level":100},"Reasons":["This test has passed 100.00% of 24 runs on jobs ['periodic-ci-openshift-multiarch-master-nightly-4.12-ocp-e2e-aws-ovn-arm64-techpreview-serial'] in the last 14 days."]},"OpenBugs":[]}],"OverallRisk":{"Level":{"Name":"High","Level":100},"Reasons":["Maximum failed test risk: High"]},"OpenBugs":[]}

Apr 26 12:35:14.264 - 122s  E alert/KubeAPIErrorBudgetBurn ns/openshift-kube-apiserver ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="firing", long="6h", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="critical", short="30m"}
Apr 26 12:35:14.264 - 5394s E alert/Watchdog ns/openshift-monitoring ALERTS{alertname="Watchdog", alertstate="firing", namespace="openshift-monitoring", prometheus="openshift-monitoring/k8s", severity="none"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 1h28m54s on platformidentification.JobType{Release:"4.12", FromRelease:"", Platform:"aws", Architecture:"arm64", Network:"ovn", Topology:"ha"} (maxAllowed=2s): pending for 1h26m52s, firing for 2m2s:
Apr 26 12:37:16.264 - 926s  I alert/KubeAPIErrorBudgetBurn ns/openshift-kube-apiserver ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="1d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="2h"}
Apr 26 12:37:16.264 - 4286s I alert/KubeAPIErrorBudgetBurn ns/openshift-kube-apiserver ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}
Apr 26 12:35:14.264 - 122s  E alert/KubeAPIErrorBudgetBurn ns/openshift-kube-apiserver ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="firing", long="6h", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="critical", short="30m"}

# [bz-kube-apiserver][invariant] alert/KubeAPIErrorBudgetBurn should not be at or above pending
KubeAPIErrorBudgetBurn was at or above pending for at least 7m36s on platformidentification.JobType{Release:"4.12", FromRelease:"", Platform:"aws", Architecture:"arm64", Network:"ovn", Topology:"ha"} (maxAllowed=2s): pending for 7m36s, firing for 0s:
Apr 23 17:25:19.906 - 78s   I alert/KubeAPIErrorBudgetBurn ns/openshift-kube-apiserver ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="1d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="2h"}
Apr 23 17:25:19.906 - 378s  I alert/KubeAPIErrorBudgetBurn ns/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 2m26s on platformidentification.JobType{Release:"4.12", FromRelease:"", Platform:"aws", Architecture:"arm64", Network:"ovn", Topology:"ha"} (maxAllowed=2s): pending for 2m26s, firing for 0s:
Apr 25 00:33:16.413 - 146s  I alert/KubeAPIErrorBudgetBurn ns/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 2m48s on platformidentification.JobType{Release:"4.12", FromRelease:"", Platform:"aws", Architecture:"arm64", Network:"ovn", Topology:"ha"} (maxAllowed=2s): pending for 2m48s, firing for 0s:
Apr 23 10:14:30.807 - 168s  I alert/KubeAPIErrorBudgetBurn ns/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 2m40s on platformidentification.JobType{Release:"4.12", FromRelease:"", Platform:"aws", Architecture:"arm64", Network:"ovn", Topology:"ha"} (maxAllowed=2s): pending for 2m40s, firing for 0s:
Apr 22 07:55:42.250 - 160s  I alert/KubeAPIErrorBudgetBurn ns/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 1m12s on platformidentification.JobType{Release:"4.12", FromRelease:"", Platform:"aws", Architecture:"arm64", Network:"ovn", Topology:"ha"} (maxAllowed=2s): pending for 1m12s, firing for 0s:
Apr 20 11:42:15.159 - 72s   I alert/KubeAPIErrorBudgetBurn ns/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 27m12s on platformidentification.JobType{Release:"4.12", FromRelease:"", Platform:"aws", Architecture:"arm64", Network:"ovn", Topology:"ha"} (maxAllowed=2s): pending for 27m12s, firing for 0s:
Apr 18 16:25:08.298 - 156s  I alert/KubeAPIErrorBudgetBurn ns/openshift-kube-apiserver ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="1d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="2h"}
Apr 18 16:25:08.298 - 1476s I alert/KubeAPIErrorBudgetBurn ns/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 5m40s on platformidentification.JobType{Release:"4.12", FromRelease:"", Platform:"aws", Architecture:"arm64", Network:"ovn", Topology:"ha"} (maxAllowed=2s): pending for 5m40s, firing for 0s:
Apr 18 10:02:53.266 - 340s  I alert/KubeAPIErrorBudgetBurn ns/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 1m32s on platformidentification.JobType{Release:"4.12", FromRelease:"", Platform:"aws", Architecture:"arm64", Network:"ovn", Topology:"ha"} (maxAllowed=2s): pending for 1m32s, firing for 0s:
Apr 18 12:54:16.371 - 92s   I alert/KubeAPIErrorBudgetBurn ns/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:"4.12", FromRelease:"", Platform:"aws", Architecture:"arm64", Network:"ovn", Topology:"ha"} (maxAllowed=2s): pending for 1m28s, firing for 0s:
Apr 15 21:09:20.016 - 88s   I alert/KubeAPIErrorBudgetBurn ns/openshift-kube-apiserver ALERTS{alertname="KubeAPIErrorBudgetBurn", alertstate="pending", long="3d", namespace="openshift-kube-apiserver", prometheus="openshift-monitoring/k8s", severity="warning", short="6h"}