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docs: clarifies scale down operation by CA in FAQ.md and main.go 

This commit clarifies the condition when a node can be scaled down by the Cluster Autoscaler (CA).
The changes updates the section and flag description in the FAQ.md and main.go files.
This commit is contained in:
faan11 2024-01-07 23:36:53 +01:00
parent 6a7e6a23f4
commit 6ec725638c
2 changed files with 3 additions and 3 deletions
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4
cluster-autoscaler/FAQ.md
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@ -590,7 +590,7 @@ any nodes left unregistered after this time.
Every 10 seconds (configurable by `--scan-interval` flag), if no scale-up is
needed, Cluster Autoscaler checks which nodes are unneeded. A node is considered for removal when **all** below conditions hold:
* The sum of cpu and memory requests of all pods running on this node ([DaemonSet pods](https://kubernetes.io/docs/concepts/workloads/controllers/daemonset/) and [Mirror pods](https://kubernetes.io/docs/tasks/configure-pod-container/static-pod/) are included by default but this is configurable with `--ignore-daemonsets-utilization` and `--ignore-mirror-pods-utilization` flags) is smaller
* The sum of cpu requests and sum of memory requests of all pods running on this node ([DaemonSet pods](https://kubernetes.io/docs/concepts/workloads/controllers/daemonset/) and [Mirror pods](https://kubernetes.io/docs/tasks/configure-pod-container/static-pod/) are included by default but this is configurable with `--ignore-daemonsets-utilization` and `--ignore-mirror-pods-utilization` flags) are smaller
than 50% of the node's allocatable. (Before 1.1.0, node capacity was used
instead of allocatable.) Utilization threshold can be configured using
`--scale-down-utilization-threshold` flag.
@ -770,7 +770,7 @@ The following startup parameters are supported for cluster autoscaler:
| `scale-down-delay-after-failure` | How long after scale down failure that scale down evaluation resumes | 3 minutes
| `scale-down-unneeded-time` | How long a node should be unneeded before it is eligible for scale down | 10 minutes
| `scale-down-unready-time` | How long an unready node should be unneeded before it is eligible for scale down | 20 minutes
| `scale-down-utilization-threshold` | Node utilization level, defined as sum of requested resources divided by capacity, below which a node can be considered for scale down | 0.5
| `scale-down-utilization-threshold` | The maximum value between the sum of cpu requests and sum of memory requests of all pods running on the node divided by node's corresponding allocatable resource, below which a node can be considered for scale down. This value is a floating point number that can range between zero and one. | 0.5
| `scale-down-non-empty-candidates-count` | Maximum number of non empty nodes considered in one iteration as candidates for scale down with drain<br>Lower value means better CA responsiveness but possible slower scale down latency<br>Higher value can affect CA performance with big clusters (hundreds of nodes)<br>Set to non positive value to turn this heuristic off - CA will not limit the number of nodes it considers." | 30
| `scale-down-candidates-pool-ratio` | A ratio of nodes that are considered as additional non empty candidates for<br>scale down when some candidates from previous iteration are no longer valid<br>Lower value means better CA responsiveness but possible slower scale down latency<br>Higher value can affect CA performance with big clusters (hundreds of nodes)<br>Set to 1.0 to turn this heuristics off - CA will take all nodes as additional candidates. | 0.1
| `scale-down-candidates-pool-min-count` | Minimum number of nodes that are considered as additional non empty candidates<br>for scale down when some candidates from previous iteration are no longer valid.<br>When calculating the pool size for additional candidates we take<br>`max(#nodes * scale-down-candidates-pool-ratio, scale-down-candidates-pool-min-count)` | 50

2
cluster-autoscaler/main.go
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@ -121,7 +121,7 @@ var (
scaleDownUnreadyTime = flag.Duration("scale-down-unready-time", config.DefaultScaleDownUnreadyTime,
"How long an unready node should be unneeded before it is eligible for scale down")
scaleDownUtilizationThreshold = flag.Float64("scale-down-utilization-threshold", config.DefaultScaleDownUtilizationThreshold,
"Sum of cpu or memory of all pods running on the node divided by node's corresponding allocatable resource, below which a node can be considered for scale down")
"The maximum value between the sum of cpu requests and sum of memory requests of all pods running on the node divided by node's corresponding allocatable resource, below which a node can be considered for scale down")
scaleDownGpuUtilizationThreshold = flag.Float64("scale-down-gpu-utilization-threshold", config.DefaultScaleDownGpuUtilizationThreshold,
"Sum of gpu requests of all pods running on the node divided by node's allocatable resource, below which a node can be considered for scale down."+
"Utilization calculation only cares about gpu resource for accelerator node. cpu and memory utilization will be ignored.")