bugfix: refactor alerts to accomodate for single-node clusters #1010
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For the sake of brevity, let:
Q: kube_node_status_allocatable{job="kube-state-metrics",resource="cpu"} (allocable), and,
QQ: namespace_cpu:kube_pod_container_resource_requests:sum{} (requested), thus,
both quota alerts relevant here exist in the form: sum(QQ) by (cluster) - (sum(Q) by (cluster) - max(Q) by (cluster)) > 0 and (sum(Q) by (cluster) - max(Q) by (cluster)) > 0,
which, in case of a single-node cluster (sum(Q) by (cluster) = max(Q) by (cluster)), is reduced to,
sum(QQ) by (cluster) > 0, i.e., the alert will fire if *any* request limits exist.
To address this, drop the "max(Q) by (cluster)" buffer assumed in
non-SNO clusters from SNO, reducing the expression to: sum(QQ) by (cluster) - sum(Q) by (cluster) > 0 (total requeted - total allocable > 0 to trigger alert),
since there is only a single node, so a buffer of the same sort does not
make sense.
Signed-off-by: Pranshu Srivastava <[email protected]>
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rexagod
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Jan 6, 2025
| and | ||
| (sum(kube_node_status_allocatable{%(kubeStateMetricsSelector)s,resource="cpu"}) by (%(clusterLabel)s) - max(kube_node_status_allocatable{%(kubeStateMetricsSelector)s,resource="cpu"}) by (%(clusterLabel)s)) > 0 | ||
| sum(namespace_cpu:kube_pod_container_resource_requests:sum{%(ignoringOverprovisionedWorkloadSelector)s}) by (%(clusterLabel)s) - | ||
| sum(kube_node_status_allocatable{%(kubeStateMetricsSelector)s,resource="cpu"}) by (%(clusterLabel)s) > 0) |
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Suggested change
| sum(kube_node_status_allocatable{%(kubeStateMetricsSelector)s,resource="cpu"}) by (%(clusterLabel)s) > 0) | |
| 0.95 * sum(kube_node_status_allocatable{%(kubeStateMetricsSelector)s,resource="cpu"}) by (%(clusterLabel)s) > 0) |
Since a max(Q) buffer is not applicable in SNO, how about a numeric buffer of 5% (or more?)? That should help alert before things go out of budget.
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skl
reviewed
Jan 7, 2025
| @@ -34,18 +34,34 @@ | |||
| } + | |||
| if $._config.showMultiCluster then { | |||
| expr: ||| | |||
| sum(namespace_cpu:kube_pod_container_resource_requests:sum{%(ignoringOverprovisionedWorkloadSelector)s}) by (%(clusterLabel)s) - (sum(kube_node_status_allocatable{%(kubeStateMetricsSelector)s,resource="cpu"}) by (%(clusterLabel)s) - max(kube_node_status_allocatable{%(kubeStateMetricsSelector)s,resource="cpu"}) by (%(clusterLabel)s)) > 0 | |||
| (count(kube_node_info) == 1 | |||
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If showMultiCluster is true that implies the cluster label is available, so the check here should probably use the cluster label (so that each cluster is checked on whether it has a single node).
Additionally, I suggest a de-dupe for multiple KSM using max like so:
Suggested change
| (count(kube_node_info) == 1 | |
| (count by (cluster) (max by (cluster, node) (kube_node_info)) == 1 |
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| and | ||
| (sum(kube_node_status_allocatable{%(kubeStateMetricsSelector)s,resource="cpu"}) by (%(clusterLabel)s) - | ||
| max(kube_node_status_allocatable{%(kubeStateMetricsSelector)s,resource="cpu"}) by (%(clusterLabel)s)) > 0) |
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From what I gather here, this pre-existing latter part of the and effectively removes single-node clusters (because "sum(cpu) - max(cpu)" can never be greater than zero on a single-node cluster).
This seems to conflict with the PR description:
the alert will fire if any request limits exist
Can you be more specific or provide a test case where the existing rule is not behaving as expected? Maybe this particular alert isn't affected?
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For the sake of brevity, let:
thus, both quota alert expressions relevant here (
KubeCPUOvercommitandKubeMemoryOvercommit) exist in the form:sum(QQ) by (cluster) - (sum(Q) by (cluster) - max(Q) by (cluster)) > 0 and (sum(Q) by (cluster) - max(Q) by (cluster)) > 0, which, in case of a single-node cluster (sum(Q) by (cluster)=max(Q) by (cluster)), is reduced to,sum(QQ) by (cluster) > 0, i.e., the alert will fire if any request limits exist.To address this, drop the
max(Q) by (cluster)buffer assumed in non-SNO clusters from SNO, reducing the expression to:sum(QQ) by (cluster) - sum(Q) by (cluster) > 0(total requeted - total allocable > 0 to trigger alert), since there is only a single node, so a buffer of the same sort does not make sense.