kubelet

The kubelet component runs on each node in a Kubernetes cluster, which serves as the primary administrative agent for each node, monitoring application servers and routing administrative requests to servers. You can configure kubelet for all cluster nodes through the kubelet section of the MKE configuration file, an example of which follows:

spec:
  kubelet:
    eventRecordQPS: 50
    maxPods: 110
    podPidsLimit: -1
    podsPerCore: 0
    protectKernelDefaults: false
    seccompDefault: false
    workerKubeReserved:
      cpu: 50m
      ephemeral-storage: 500Mi
      memory: 300Mi
    managerKubeReserved:
      cpu: 250m
      ephemeral-storage: 4Gi
      memory: 2Gi

You can further configure a kubelet using the extraArgs field to define flags. This field accepts a list of key-value pairs, which are passed directly to the kubelet process at runtime.

Example extraArgs field configuration:

spec:
  kubelet:
    extraArgs:
      event-burst: 100
      event-qps: 50

You can also configure a kubelet with custom profiles. Such profiles offer greater control of the KubeletConfiguration and can be targeted to specific hosts.

kubelet custom profiles

You can deploy custom profiles to configure kubelet on a per-node basis.

A kubelet custom profile comprises a profile name and a set of values. The profile name identifies the profile and targets it to specific nodes in the cluster, while the values are merged into the final kubelet configuration that is applied to a target node.

Create a custom profile

You can specify custom profiles in the kubelet.customProfiles section of the MKE configuration file. Profiles must each have a unique name, and values can refer to fields in the kubelet configuration file.

For detail on all possible values, refer to the official Kubernetes documentation Set Kubelet Parameters Via A Configuration File.

The following example configuration creates a custom profile named hardworker that specifies thresholds for the garbage collection of images and eviction:

spec:
  kubelet:
    customProfiles:
      - name: hardworker
        values:
          imageGCHighThresholdPercent: 85
          imageGCLowThresholdPercent: 80
          evictionHard:
            imagefs.available: 15%
            memory.available: 100Mi
            nodefs.available: 10%
            nodefs.inodesFree: 5%

Apply a custom profile to a node

Hosts can be assigned a custom profile through the hosts section of the MKE configuration file, whereas the profile name is an installation time argument for the host.

The following example configuration applies the hardworker custom profile to the localhost node:

  hosts:
  - role: single
    ssh:
      address: localhost
      keyPath: ~/.ssh/id_rsa
      port: 22
      user: root
      installFlags:
        - --profile=hardworker

Precedence of kubelet configuration

The kubelet configuration of each node is created by merging several different configuration sources. For MKE 4, the order is as follows:

1. Structured configuration values specified in the kubelet section of the MKE configuration, which is the lowest precedence.
2. Custom profile values specified in kublelet.customProfiles.
3. Runtime flags specified in kubelet.extraArgs, which is the highest precedence.

For more information on kubelet configuration value precedence, refer to the official Kubernetes documentation Kubelet configuration merging order.