18-containers-Runtime Class

concepts/containers/runtime-class/

FEATURE STATE: Kubernetes v1.14 beta

此頁描述RuntimeClass資源和執行時選擇機制。

Warning: RuntimeClass includes breaking changes in the beta upgrade in v1.14. If you were using RuntimeClass prior to v1.14, see Upgrading RuntimeClass from Alpha to Beta.

Runtime Class

RuntimeClass是用於選擇容器執行時配置的功能。容器執行時配置用於執行pod的容器。

Motivation

You can set a different RuntimeClass between different Pods to provide a balance of performance versus security. For example, if part of your workload deserves a high level of information security assurance, you might choose to schedule those Pods so that they run in a container runtime that uses hardware virtualization. You’d then benefit from the extra isolation of the alternative runtime, at the expense of some additional overhead.您可以在不同的pod之間設定不同的執行時類，以提供效能與安全性之間的平衡。例如，如果部分工作負載需要高階別的資訊保安保證，則可以選擇安排這些pod，以便它們在使用硬體虛擬化的容器執行時中執行。然後，您將從替代執行時的額外隔離中獲益，同時犧牲一些額外的開銷。

You can also use RuntimeClass to run different Pods with the same container runtime but with different settings.您還可以使用RuntimeClass使用相同的容器執行時執行不同的播客，但使用不同的設定。

Set Up

確保已啟用RuntimeClass功能入口（預設情況下為啟用狀態）。有關啟用功能門的說明，請參閱功能門,必須在apiservers和kubelets上啟用“runtimeclass”功能門。

在節點上配置cri實現（依賴於執行時）
建立相應的RuntimeClass資源

1. Configure the CRI implementation on nodes

configure. 通過RuntimeClass可用的配置依賴於容器執行時介面（CRI）實現。有關如何配置的CRI實現，請參見相應的文件 (below)

Note: RuntimeClass assumes a homogeneous node configuration across the cluster by default (which means that all nodes are configured the same way with respect to container runtimes). To support heterogenous node configurations, see Scheduling below.

The configurations have a corresponding handler name, referenced by the RuntimeClass. The handler must be a valid DNS 1123 label (alpha-numeric + - characters).

2. Create the corresponding RuntimeClass resources

The configurations setup in step 1 should each have an associated handler name, which identifies the configuration. For each handler, create a corresponding RuntimeClass object.

The RuntimeClass resource currently only has 2 significant fields: the RuntimeClass name (metadata.name) and the handler (handler). The object definition looks like this:

apiVersion: node.k8s.io/v1beta1  # RuntimeClass is defined in the node.k8s.io API group
kind: RuntimeClass
metadata:
  name: myclass  # The name the RuntimeClass will be referenced by
  # RuntimeClass is a non-namespaced resource
handler: myconfiguration  # The name of the corresponding CRI configuration

Note: It is recommended that RuntimeClass write operations (create/update/patch/delete) be restricted to the cluster administrator. This is typically the default. See Authorization Overview for more details.

Usage

Once RuntimeClasses are configured for the cluster, using them is very simple. Specify a runtimeClassName in the Pod spec. For example:

apiVersion: v1
kind: Pod
metadata:
  name: mypod
spec:
  runtimeClassName: myclass
  # ...

This will instruct the Kubelet to use the named RuntimeClass to run this pod. If the named RuntimeClass does not exist, or the CRI cannot run the corresponding handler, the pod will enter the Failed terminal phase. Look for a corresponding event for an error message.

If no runtimeClassName is specified, the default RuntimeHandler will be used, which is equivalent to the behavior when the RuntimeClass feature is disabled.

CRI Configuration

For more details on setting up CRI runtimes, see CRI installation.

dockershim

Kubernetes built-in dockershim CRI does not support runtime handlers.

containerd

Runtime handlers are configured through containerd’s configuration at /etc/containerd/config.toml. Valid handlers are configured under the runtimes section:

[plugins.cri.containerd.runtimes.${HANDLER_NAME}]

See containerd’s config documentation for more details: https://github.com/containerd/cri/blob/mas...

cri-o

Runtime handlers are configured through cri-o’s configuration at /etc/crio/crio.conf. Valid handlers are configured under the crio.runtime table:

[crio.runtime.runtimes.${HANDLER_NAME}]
  runtime_path = "${PATH_TO_BINARY}"

See cri-o’s config documentation for more details: https://github.com/kubernetes-sigs/cri-o/b...

Scheduling

FEATURE STATE: Kubernetes v1.16 beta

As of Kubernetes v1.16, RuntimeClass includes support for heterogenous clusters through its scheduling fields. Through the use of these fields, you can ensure that pods running with this RuntimeClass are scheduled to nodes that support it. To use the scheduling support, you must have the RuntimeClass admission controller enabled (the default, as of 1.16).

To ensure pods land on nodes supporting a specific RuntimeClass, that set of nodes should have a common label which is then selected by the runtimeclass.scheduling.nodeSelector field. The RuntimeClass’s nodeSelector is merged with the pod’s nodeSelector in admission, effectively taking the intersection of the set of nodes selected by each. If there is a conflict, the pod will be rejected.

If the supported nodes are tainted to prevent other RuntimeClass pods from running on the node, you can add tolerations to the RuntimeClass. As with the nodeSelector, the tolerations are merged with the pod’s tolerations in admission, effectively taking the union of the set of nodes tolerated by each.

To learn more about configuring the node selector and tolerations, see Assigning Pods to Nodes.

Pod Overhead

FEATURE STATE: Kubernetes v1.16 alpha

As of Kubernetes v1.16, RuntimeClass includes support for specifying overhead associated with running a pod, as part of the PodOverhead feature. To use PodOverhead, you must have the PodOverhead feature gate enabled (it is off by default).

Pod overhead is defined in RuntimeClass through the Overhead fields. Through the use of these fields, you can specify the overhead of running pods utilizing this RuntimeClass and ensure these overheads are accounted for in Kubernetes.

Upgrading RuntimeClass from Alpha to Beta

The RuntimeClass Beta feature includes the following changes:

The node.k8s.io API group and runtimeclasses.node.k8s.io resource have been migrated to a built-in API from a CustomResourceDefinition.
The spec has been inlined in the RuntimeClass definition (i.e. there is no more RuntimeClassSpec).
The runtimeHandler field has been renamed handler.
The handler field is now required in all API versions. This means the runtimeHandler field in the Alpha API is also required.
The handler field must be a valid DNS label (RFC 1123), meaning it can no longer contain . characters (in all versions). Valid handlers match the following regular expression: ^[a-z0-9]([-a-z0-9]*[a-z0-9])?$.

Action Required: The following actions are required to upgrade from the alpha version of the RuntimeClass feature to the beta version:

RuntimeClass resources must be recreated after upgrading to v1.14, and the runtimeclasses.node.k8s.io CRD should be manually deleted: kubectl delete customresourcedefinitions.apiextensions.k8s.io runtimeclasses.node.k8s.io
Alpha RuntimeClasses with an unspecified or empty runtimeHandler or those using a . character in the handler are no longer valid, and must be migrated to a valid handler configuration (see above).