Managing nodes

You can manage nodes in your instance using the CLI.

When you perform node management operations, the CLI interacts with node objects that are representations of actual node hosts. The master uses the information from node objects to validate nodes with health checks.

To list all nodes that are known to the master:

To only list information about a single node, replace <node> with the full node name:

The STATUS column in the output of these commands can show nodes with the following conditions:

To get more detailed information about a specific node, including the reason for the current condition:

For example:

You can display usage statistics about nodes, which provide the runtime environments for containers. These usage statistics include CPU, memory, and storage consumption.

To view the usage statistics:

To view the usage statistics for nodes with labels:

You must choose the selector (label query) to filter on. Supports =, ==, and !=.

To add nodes to your existing OKD cluster, you can run an Ansible playbook that handles installing the node components, generating the required certificates, and other important steps. See the advanced installation method for instructions on running the playbook directly.

When you delete a node using the CLI, the node object is deleted in Kubernetes, but the pods that exist on the node itself are not deleted. Any bare pods not backed by a replication controller would be inaccessible to OKD, pods backed by replication controllers would be rescheduled to other available nodes, and local manifest pods would need to be manually deleted.

To delete a node from the OKD cluster:

To add or update labels on a node:

To see more detailed usage:

To list all or selected pods on one or more nodes:

To list all or selected pods on selected nodes:

By default, healthy nodes with a Ready status are marked as schedulable, meaning that new pods are allowed for placement on the node. Manually marking a node as unschedulable blocks any new pods from being scheduled on the node. Existing pods on the node are not affected.

To mark a node or nodes as unschedulable:

For example:

To mark a currently unschedulable node or nodes as schedulable:

Alternatively, instead of specifying specific node names (e.g., <node1> <node2>), you can use the --selector=<node_selector> option to mark selected nodes as schedulable or unschedulable.

Evacuating pods allows you to migrate all or selected pods from a given node or nodes. Nodes must first be marked unschedulable to perform pod evacuation.

Only pods backed by a replication controller can be evacuated; the replication controllers create new pods on other nodes and remove the existing pods from the specified node(s). Bare pods, meaning those not backed by a replication controller, are unaffected by default. You can evacuate a subset of pods by specifying a pod-selector. Pod selector is based on labels, so all the pods with the specified label will be evacuated.

To list pods that will be migrated without actually performing the evacuation, use the --dry-run option:

To actually evacuate all or selected pods on one or more nodes:

You can force deletion of bare pods by using the --force option:

Alternatively, instead of specifying specific node names (e.g., <node1> <node2>), you can use the --selector=<node_selector> option to evacuate pods on selected nodes.

To list objects that will be migrated without actually performing the evacuation, use the --dry-run option and set it to true:

To reboot a node without causing an outage for applications running on the platform, it is important to first evacuate the pods. For pods that are made highly available by the routing tier, nothing else needs to be done. For other pods needing storage, typically databases, it is critical to ensure that they can remain in operation with one pod temporarily going offline. While implementing resiliency for stateful pods is different for each application, in all cases it is important to configure the scheduler to use node anti-affinity to ensure that the pods are properly spread across available nodes.

Another challenge is how to handle nodes that are running critical infrastructure such as the router or the registry. The same node evacuation process applies, though it is important to understand certain edge cases.

You can configure node resources by adding kubelet arguments to the node configuration file (/etc/origin/node/node-config.yaml). Add the kubeletArguments section and include any desired options:

To view all available kubelet options:

This can also be set during an advanced installation using the openshift_node_kubelet_args variable. For example:

As you download Docker images and run and delete containers, Docker does not always free up mapped disk space. As a result, over time you can run out of space on a node, which might prevent OKD from being able to create new pods or cause pod creation to take several minutes.

For example, the following shows pods that are still in the ContainerCreating state after six minutes and the events log shows a FailedSync event.

One solution to this problem is to reset Docker storage to remove artifacts not needed by Docker.

On the node where you want to restart Docker storage:

By default, DNS routes all node traffic. During node registration, the master receives the node IP addresses from the DNS configuration, and therefore accessing nodes via DNS is the most flexible solution for most deployments.

If your deployment is using a cloud provider, then the node gets the IP information from the cloud provider. However, openshift-sdn attempts to determine the IP through a variety of methods, including a DNS lookup on the nodeName (if set), or on the system hostname (if nodeName is not set).

However, you may need to change the node traffic interface. For example, where:

Configuring the openshift_set_node_ip Ansible variable forces node traffic through an interface other than the default network interface.

To change the node traffic interface: