52 lines
2.1 KiB
Markdown
52 lines
2.1 KiB
Markdown
---
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title: Container Runtime Interface (CRI)
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content_type: concept
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weight: 50
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---
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<!-- overview -->
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The CRI is a plugin interface which enables the kubelet to use a wide variety of
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container runtimes, without having a need to recompile the cluster components.
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You need a working
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{{<glossary_tooltip text="container runtime" term_id="container-runtime">}} on
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each Node in your cluster, so that the
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{{< glossary_tooltip text="kubelet" term_id="kubelet" >}} can launch
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{{< glossary_tooltip text="Pods" term_id="pod" >}} and their containers.
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{{< glossary_definition prepend="The Container Runtime Interface (CRI) is" term_id="container-runtime-interface" length="all" >}}
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<!-- body -->
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## The API {#api}
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{{< feature-state for_k8s_version="v1.23" state="stable" >}}
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The kubelet acts as a client when connecting to the container runtime via gRPC.
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The runtime and image service endpoints have to be available in the container
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runtime, which can be configured separately within the kubelet by using the
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`--image-service-endpoint` and `--container-runtime-endpoint` [command line
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flags](/docs/reference/command-line-tools-reference/kubelet)
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For Kubernetes v{{< skew currentVersion >}}, the kubelet prefers to use CRI `v1`.
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If a container runtime does not support `v1` of the CRI, then the kubelet tries to
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negotiate any older supported version.
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The v{{< skew currentVersion >}} kubelet can also negotiate CRI `v1alpha2`, but
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this version is considered as deprecated.
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If the kubelet cannot negotiate a supported CRI version, the kubelet gives up
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and doesn't register as a node.
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## Upgrading
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When upgrading Kubernetes, then the kubelet tries to automatically select the
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latest CRI version on restart of the component. If that fails, then the fallback
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will take place as mentioned above. If a gRPC re-dial was required because the
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container runtime has been upgraded, then the container runtime must also
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support the initially selected version or the redial is expected to fail. This
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requires a restart of the kubelet.
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## {{% heading "whatsnext" %}}
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- Learn more about the CRI [protocol definition](https://github.com/kubernetes/cri-api/blob/c75ef5b/pkg/apis/runtime/v1/api.proto)
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