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Clarify selection of default HPA scaling policy 

Without first mentioning where the number 40 is coming from, it was a bit unclear why 40 would be the threshold value for policy selection in this case.
I hope this patch clarifies it.
This commit is contained in:
Jack Henschel 2021-02-10 12:23:04 +01:00
parent 8377d08841
commit a33e903e3a
1 changed files with 7 additions and 6 deletions
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13
content/en/docs/tasks/run-application/horizontal-pod-autoscale.md
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@ -383,7 +383,12 @@ behavior:
periodSeconds: 60 periodSeconds: 60
``` ```
When the number of pods is more than 40 the second policy will be used for scaling down. `periodSeconds` indicates the length of time in the past for which the policy must hold true.
The first policy _(Pods)_ allows at most 4 replicas to be scaled down in one minute. The second policy
_(Percent)_ allows at most 10% of the current replicas to be scaled down in one minute.
Since by default the policy which allows the highest amount of change is selected, the second policy will
only be used when the number of pod replicas is more than 40. With 40 or less replicas, the first policy will be applied.
For instance if there are 80 replicas and the target has to be scaled down to 10 replicas For instance if there are 80 replicas and the target has to be scaled down to 10 replicas
then during the first step 8 replicas will be reduced. In the next iteration when the number then during the first step 8 replicas will be reduced. In the next iteration when the number
of replicas is 72, 10% of the pods is 7.2 but the number is rounded up to 8. On each loop of of replicas is 72, 10% of the pods is 7.2 but the number is rounded up to 8. On each loop of
@ -391,10 +396,6 @@ the autoscaler controller the number of pods to be change is re-calculated based
of current replicas. When the number of replicas falls below 40 the first policy _(Pods)_ is applied of current replicas. When the number of replicas falls below 40 the first policy _(Pods)_ is applied
and 4 replicas will be reduced at a time. and 4 replicas will be reduced at a time.
`periodSeconds` indicates the length of time in the past for which the policy must hold true.
The first policy allows at most 4 replicas to be scaled down in one minute. The second policy
allows at most 10% of the current replicas to be scaled down in one minute.
The policy selection can be changed by specifying the `selectPolicy` field for a scaling The policy selection can be changed by specifying the `selectPolicy` field for a scaling
direction. By setting the value to `Min` which would select the policy which allows the direction. By setting the value to `Min` which would select the policy which allows the
smallest change in the replica count. Setting the value to `Disabled` completely disables smallest change in the replica count. Setting the value to `Disabled` completely disables
@ -441,7 +442,7 @@ behavior:
periodSeconds: 15 periodSeconds: 15
selectPolicy: Max selectPolicy: Max
``` ```
For scaling down the stabilization window is _300_ seconds(or the value of the For scaling down the stabilization window is _300_ seconds (or the value of the
`--horizontal-pod-autoscaler-downscale-stabilization` flag if provided). There is only a single policy `--horizontal-pod-autoscaler-downscale-stabilization` flag if provided). There is only a single policy
for scaling down which allows a 100% of the currently running replicas to be removed which for scaling down which allows a 100% of the currently running replicas to be removed which
means the scaling target can be scaled down to the minimum allowed replicas. means the scaling target can be scaled down to the minimum allowed replicas.