Reconfiguring Kubelet in a live cluster

Dynamic Kubelet configuration is available as Beta in Kubernetes 1.11.

You can use this feature in IBM® Cloud Private to change the configuration of each Kubelet in a live Kubernetes cluster. To do so, you deploy a ConfigMap and configure each Node to use the ConfigMap.

For more information, see Reconfigure a Node's Kubelet in a Live Cluster Opens in a new tab . Make sure that you read the warnings.

Follow these steps to reconfigure Kubelet on a live node in your cluster:

Note: In IBM Cloud Private, the --dynamic-config-dir is set to /etc/cfc/kubelet/kubelet-dynamic-config by default.

Before you begin, ensure that kubectl CLI is set up. For more information, see Accessing your cluster from the Kubernetes CLI (kubectl).

Generate a file with the current configuration

Generate a configuration file that contains a node’s current configuration. Pick one of the following two ways:

Use the /etc/cfc/kubelet/kubelet-service-config file to create the first Kubelet ConfigMap.
Access the Kubelet server’s configz endpoint through the kubectl proxy. For more information, see Generate the configuration file for more information.

The /etc/cfc/kubelet/kubelet-service-config file is used in following sections to update the Kubelet configuration.

Edit the configuration file

Complete these steps to edit the configuration file:

Copy /etc/cfc/kubelet/kubelet-service-config to ./kubelet-dynamic-config.
```
cp /etc/cfc/kubelet/kubelet-service-config ./kubelet-dynamic-config
```

Edit the ./kubelet-dynamic-config file as required. For example, you can add resource reservations by updating the following configuration settings:

systemReserved:
  cpu: "500m"
  memory: "1500Mi"
  ephemeral-storage: "1Gi"
kubeReserved:
  cpu: "500m"
  memory: "1500Mi"
  ephemeral-storage: "1Gi"

For a list of available parameters, see the KubeletConfiguration contains the configuration for the Kubelet section of the Kubernetes sample file Opens in a new tab .

Push the configuration file to the control plane

Create the ConfigMap by pushing the configuration file to the control plane.

kubectl -n kube-system create configmap my-node-config --from-file=kubelet=kubelet-dynamic-config --append-hash -o yaml

The output resembles the following code:

apiVersion: v1
data:
  kubelet: |
    {...}
kind: ConfigMap
metadata:
  creationTimestamp: 2017-09-14T20:23:33Z
  name: my-node-config-gkt4c2m4b2
  namespace: kube-system
  resourceVersion: "119980"
  selfLink: /api/v1/namespaces/kube-system/configmaps/my-node-config-gkt4c2m4b2
  uid: 946d785e-998a-11e7-a8dd-42010a800006

The ConfigMap is created in the kube-system namespace. The --append-hash option appends a short checksum of the ConfigMap contents to the name.

Set the node to use the new configuration

Store the node name or IP address, and the ConfigMap name to two variables. See the following example commands:

  NODE_NAME=10.10.25.11

  CONFIG_MAP_NAME=my-node-config-gkt4c2m4b2

Run the following command to update the configuration of the node:

kubectl patch node ${NODE_NAME} -p "{\"spec\":{\"configSource\":{\"configMap\":{\"name\":\"${CONFIG_MAP_NAME}\",\"namespace\":\"kube-system\",\"kubeletConfigKey\":\"kubelet\"}}}}"

Note: You can write a script to update the configuration of multiple nodes.

Verify the updates

Retrieve the node information and check Node.Status.Config:

kubectl get node ${NODE_NAME} -o yaml

For more information, see Observe that the Node begins using the new configuration Opens in a new tab .

Revert to the local default configuration

Reset the node to use the default configuration.

Edit the node:
```
kubectl edit node ${NODE_NAME}
```

Remove the Node.Spec.ConfigSource field. For example, remove all of the following lines.

 configSource:
     configMap:
         name: CONFIG_MAP_NAME
         namespace: kube-system
         kubeletConfigKey: kubelet

Verify the update.
```
kubectl get node ${NODE_NAME} -o yaml
```

The Node.Status.Config is empty because you reset all the configuration sources to nil when you removed the Node.Spec.ConfigSource field. The local default configuration is now the assigned, active, and lastKnownGood configuration.