Fix nits in the Evented PLEG page
There are typos and inaccuracies in the current page. This PR fixes them.pull/40906/head
Qiming Teng
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7bdcd3da4c
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5130686665
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@ -5,88 +5,97 @@ content_type: task
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weight: 90
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---
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{{< feature-state for_k8s_version="v1.26" state="beta" >}}
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{{< feature-state for_k8s_version="v1.27" state="beta" >}}
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<!-- overview -->
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This page shows how to migrate notes to use event based updates for container status. The event-based
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This page shows how to migrate nodes to use event based updates for container status. The event-based
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implementation reduces node resource consumption by the kubelet, compared to the legacy approach
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that relies on polling.
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You may know this feature as _evented Pod lifecycle event generator (PLEG)_. That's the name used
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internally within the Kubernetes project for a key implementation detail.
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The polling based approach is referred to as _generic PLEG_.
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## {{% heading "prerequisites" %}}
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* You need to run a version of Kubernetes that provides this feature.
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Kubernetes {{< skew currentVersion >}} includes beta support for event-based container
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status updates. The feature is beta and is disabled by default.
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{{< version-check >}}
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Kubernetes v1.27 includes beta support for event-based container
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status updates. The feature is beta but is _disabled_ by default
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because it requires support from the container runtime.
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* {{< version-check >}}
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If you are running a different version of Kubernetes, check the documentation for that release.
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* The container runtime in use must support container lifecycle events.
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The kubelet automatically switches back to the legacy generic PLEG
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mechanism if the container runtime does not announce support for
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container lifecycle events, even if you have this feature gate enabled.
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<!-- steps -->
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## Why switch to Evented PLEG?
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* The current `Generic PLEG` incurs non-negligible overhead due to frequent polling of container statuses.
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* This overhead is exacerbated by Kubelet's parallelism, limiting its scalability
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and causing poor performance and reliability problems.
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* The goal of `Evented PLEG` is to reduce unnecessary work during inactivity by replacing periodic polling.
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* The _Generic PLEG_ incurs non-negligible overhead due to frequent polling of container statuses.
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* This overhead is exacerbated by Kubelet's parallelized polling of container states, thus limiting
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its scalability and causing poor performance and reliability problems.
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* The goal of _Evented PLEG_ is to reduce unnecessary work during inactivity
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by replacing periodic polling.
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## Switching to Evented PLEG
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1. Start the Kubelet with the [feature gate](/docs/reference/command-line-tools-reference/feature-gates/)
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`EventedPLEG` enabled. In Kubelet feature gates can be enabled by editing
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[config file](/docs/tasks/administer-cluster/kubelet-config-file/) and restarting the Kubelet service.
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`EventedPLEG` enabled. You can manage the kubelet feature gates editing the kubelet
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[config file](/docs/tasks/administer-cluster/kubelet-config-file/) and restarting the kubelet service.
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You need to do this on each node where you are using this feature.
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2. Please make sure the node is [drained](/docs/tasks/administer-cluster/safely-drain-node/) before proceeding.
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2. Make sure the node is [drained](/docs/tasks/administer-cluster/safely-drain-node/) before proceeding.
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3. Start the `CRI Runtime` with the `Evented PLEG` support.
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3. Start the container runtime with the container event generation enabled.
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{{< tabs name="tab_with_code" >}}
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{{% tab name="containerd" %}}
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{{% tab name="Containerd" %}}
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Version 1.7+
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{{% /tab %}}
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{{% tab name="CRI-O" %}}
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Version 1.26+
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Check if the CRI-O is already configured to emit `CRI Events` by verifying the configuration:
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Check if the CRI-O is already configured to emit CRI events by verifying the configuration,
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```shell
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crio config | grep enable_pod_events
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```
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If it is enabled it should show:
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If it is enabled, the output should be similar to the following:
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```
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```none
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enable_pod_events = true
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```
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To enable it, start the cri-o daemon with the flag `--enable-pod-events=true` or using a drop in config like:
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To enable it, start the CRI-O daemon with the flag `--enable-pod-events=true` or
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use a dropin config with the following lines:
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```
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```toml
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[crio.runtime]
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enable_pod_events: true
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```
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{{% /tab %}}
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{{< /tabs >}}
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{{< version-check >}}
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4. Verify that `Evented PLEG` is in use by looking for the term `EventedPLEG` in the kubelet logs.
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4. Verify that the kubelet is using event-based container stage change monitoring.
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To check, look for the term `EventedPLEG` in the kubelet logs.
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The output is similar to this:
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The output should be similar to this:
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```
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```console
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I0314 11:10:13.909915 1105457 feature_gate.go:249] feature gates: &{map[EventedPLEG:true]}
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```
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If you have set LOG_LEVEL to 4 and above, you might see more entries that
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indicate `Evented PLEG` is in use by the kubelet.
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If you have set `--v` to 4 and above, you might see more entries that indicate
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that the kubelet is using event-based container state monitoring.
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```
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```console
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I0314 11:12:42.009542 1110177 evented.go:238] "Evented PLEG: Generated pod status from the received event" podUID=3b2c6172-b112-447a-ba96-94e7022912dc
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I0314 11:12:44.623326 1110177 evented.go:238] "Evented PLEG: Generated pod status from the received event" podUID=b3fba5ea-a8c5-4b76-8f43-481e17e8ec40
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I0314 11:12:44.714564 1110177 evented.go:238] "Evented PLEG: Generated pod status from the received event" podUID=b3fba5ea-a8c5-4b76-8f43-481e17e8ec40
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@ -94,5 +103,6 @@ internally within the Kubernetes project for a key implementation detail.
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## {{% heading "whatsnext" %}}
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* Learn more about
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[KEP 3386](https://github.com/kubernetes/enhancements/blob/5b258a990adabc2ffdc9d84581ea6ed696f7ce6c/keps/sig-node/3386-kubelet-evented-pleg/README.md).
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* Learn more about the design in the Kubernetes Enhancement Proposal (KEP):
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[Kubelet Evented PLEG for Better Performance](https://github.com/kubernetes/enhancements/blob/5b258a990adabc2ffdc9d84581ea6ed696f7ce6c/keps/sig-node/3386-kubelet-evented-pleg/README.md).
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