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content/en/blog/_posts/2022-09-14-pod-has-network-condition.md
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layout: blog | ||
title: 'Kubernetes 1.25: PodHasNetwork condition for pods' | ||
date: 2022-09-14 | ||
slug: pod-has-network-condition | ||
--- | ||
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**Author:** | ||
Deep Debroy (Apple) | ||
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Kubernetes 1.25 introduces Alpha support for a new kubelet-managed pod condition | ||
in the status field of a pod: `PodHasNetwork`. The kubelet, for a worker node, | ||
will use the `PodHasNetwork` condition to accurately surface the initialization | ||
state of a pod from the perspective of pod sandbox creation and network | ||
configuration by a container runtime (typically in coordination with CNI | ||
plugins). The kubelet starts to pull container images and start individual | ||
containers (including init containers) after the status of the `PodHasNetwork` | ||
condition is set to `True`. Metrics collection services that report latency of | ||
pod initialization from a cluster infrastructural perspective (i.e. agnostic of | ||
per container characteristics like image size or payload) can utilize the | ||
`PodHasNetwork` condition to accurately generate Service Level Indicators | ||
(SLIs). Certain operators or controllers that manage underlying pods may utilize | ||
the `PodHasNetwork` condition to optimize the set of actions performed when pods | ||
repeatedly fail to come up. | ||
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### How is this different from the existing Initialized condition reported for pods? | ||
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The kubelet sets the status of the existing `Initialized` condition reported in | ||
the status field of a pod depending on the presence of init containers in a pod. | ||
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If a pod specifies init containers, the status of the `Initialized` condition in | ||
the pod status will not be set to `True` until all init containers for the pod | ||
have succeeded. However, init containers, configured by users, may have errors | ||
(payload crashing, invalid image, etc) and the number of init containers | ||
configured in a pod may vary across different workloads. Therefore, | ||
cluster-wide, infrastructural SLIs around pod initialization cannot depend on | ||
the `Initialized` condition of pods. | ||
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If a pod does not specify init containers, the status of the `Initialized` | ||
condition in the pod status is set to `True` very early in the lifecycle of the | ||
pod. This occurs before the kubelet initiates any pod runtime sandbox creation | ||
and network configuration steps. As a result, a pod without init containers will | ||
report the status of the `Initialized` condition as `True` even if the container | ||
runtime is not able to successfully initialize the pod sandbox environment. | ||
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Relative to either situation above, the `PodHasNetwork` condition surfaces more | ||
accurate data around when the pod runtime sandbox was initialized with | ||
networking configured so that the kubelet can proceed to launch user-configured | ||
containers (including init containers) in the pod. | ||
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Note that a node agent may dynamically re-configure network interface(s) for a | ||
pod by watching changes in pod annotations that specify additional networking | ||
configuration (e.g. `k8s.v1.cni.cncf.io/networks`). Dynamic updates of pod | ||
networking configuration after the pod sandbox is initialized by Kubelet (in | ||
coordination with a container runtime) are not reflected by the `PodHasNetwork` | ||
condition. | ||
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### Try out the PodHasNetwork condition for pods | ||
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In order to have the kubelet report the `PodHasNetwork` condition in the status | ||
field of a pod, please enable the `PodHasNetworkCondition` feature gate on the | ||
kubelet. | ||
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For a pod whose runtime sandbox has been successfully created and has networking | ||
configured, the kubelet will report the `PodHasNetwork` condition with status set to `True`: | ||
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``` | ||
$ kubectl describe pod nginx1 | ||
Name: nginx1 | ||
Namespace: default | ||
... | ||
Conditions: | ||
Type Status | ||
PodHasNetwork True | ||
Initialized True | ||
Ready True | ||
ContainersReady True | ||
PodScheduled True | ||
``` | ||
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For a pod whose runtime sandbox has not been created yet (and networking not | ||
configured either), the kubelet will report the `PodHasNetwork` condition with | ||
status set to `False`: | ||
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``` | ||
$ kubectl describe pod nginx2 | ||
Name: nginx2 | ||
Namespace: default | ||
... | ||
Conditions: | ||
Type Status | ||
PodHasNetwork False | ||
Initialized True | ||
Ready False | ||
ContainersReady False | ||
PodScheduled True | ||
``` | ||
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### What’s next? | ||
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Depending on feedback and adoption, the Kubernetes team plans to push the | ||
reporting of the `PodHasNetwork` condition to Beta in 1.26 or 1.27. | ||
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### How can I learn more? | ||
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Please check out the | ||
[documentation](/docs/concepts/workloads/pods/pod-lifecycle/) for the | ||
`PodHasNetwork` condition to learn more about it and how it fits in relation to | ||
other pod conditions. | ||
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### How to get involved? | ||
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This feature is driven by the SIG Node community. Please join us to connect with | ||
the community and share your ideas and feedback around the above feature and | ||
beyond. We look forward to hearing from you! | ||
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### Acknowledgements | ||
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We want to thank the following people for their insightful and helpful reviews | ||
of the KEP and PRs around this feature: Derek Carr (@derekwaynecarr), Mrunal | ||
Patel (@mrunalp), Dawn Chen (@dchen1107), Qiutong Song (@qiutongs), Ruiwen Zhao | ||
(@ruiwen-zhao), Tim Bannister (@sftim), Danielle Lancashire (@endocrimes) and | ||
Agam Dua (@agamdua). |