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88 lines
2.8 KiB
Plaintext
88 lines
2.8 KiB
Plaintext
// Module included in the following assemblies:
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//
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// * nodes/nodes-cluster-overcommit.adoc
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[id="nodes-cluster-overcommit-node-memory_{context}"]
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= Reserving memory across quality of service tiers
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You can use the `qos-reserved` parameter to specify a percentage of memory to be reserved
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by a pod in a particular QoS level. This feature attempts to reserve requested resources to exclude pods
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from lower OoS classes from using resources requested by pods in higher QoS classes.
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By reserving resources for higher QOS levels, pods that do not have resource limits are prevented from encroaching on the resources
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requested by pods at higher QoS levels.
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.Prerequisites
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. Obtain the label associated with the static Machine Config Pool CRD for the type of node you want to configure.
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Perform one of the following steps:
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.. View the Machine Config Pool:
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+
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----
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$ oc describe machineconfigpool <name>
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----
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+
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For example:
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+
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[source,yaml]
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----
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$ oc describe machineconfigpool worker
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apiVersion: machineconfiguration.openshift.io/v1
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kind: MachineConfigPool
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metadata:
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creationTimestamp: 2019-02-08T14:52:39Z
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generation: 1
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labels:
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custom-kubelet: small-pods <1>
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----
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<1> If a label has been added it appears under `labels`.
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.. If the label is not present, add a key/value pair:
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+
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----
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$ oc label machineconfigpool worker custom-kubelet=small-pods
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----
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.Procedure
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. Create a Custom Resource (CR) for your configuration change.
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+
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.Sample configuration for a disabling CPU limits
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[source,yaml]
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----
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apiVersion: machineconfiguration.openshift.io/v1
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kind: KubeletConfig
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metadata:
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name: disable-cpu-units <1>
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spec:
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machineConfigPoolSelector:
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matchLabels:
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custom-kubelet: small-pods <2>
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kubeletConfig:
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cgroups-per-qos:
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- true
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cgroup-driver:
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- 'systemd'
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cgroup-root:
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- '/'
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qos-reserved: <3>
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- 'memory=50%'
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----
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<1> Assign a name to CR.
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<2> Specify the label to apply the configuration change.
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<3> Specifies how pod resource requests are reserved at the QoS level.
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{product-title} uses the `qos-reserved` parameter as follows:
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- A value of `qos-reserved=memory=100%` will prevent the `Burstable` and `BestEffort` QOS classes from consuming memory
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that was requested by a higher QoS class. This increases the risk of inducing OOM
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on `BestEffort` and `Burstable` workloads in favor of increasing memory resource guarantees
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for `Guaranteed` and `Burstable` workloads.
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- A value of `qos-reserved=memory=50%` will allow the `Burstable` and `BestEffort` QOS classes
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to consume half of the memory requested by a higher QoS class.
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- A value of `qos-reserved=memory=0%`
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will allow a `Burstable` and `BestEffort` QoS classes to consume up to the full node
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allocatable amount if available, but increases the risk that a `Guaranteed` workload
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will not have access to requested memory. This condition effectively disables this feature.
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