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About nodes

A node is a virtual or bare-metal machine in a Kubernetes cluster. Worker nodes host your application containers, grouped as pods. The control plane nodes run services that are required to control the Kubernetes cluster. In OKD, the control plane nodes contain more than just the Kubernetes services for managing the OKD cluster.

Having stable and healthy nodes in a cluster is fundamental to the smooth functioning of your hosted application. In OKD, you can access, manage, and monitor a node through the Node object representing the node. Using the OpenShift CLI (oc) or the web console, you can perform the following operations on a node.

Read operations

The read operations allow an administrator or a developer to get information about nodes in an OKD cluster.

Management operations

As an administrator, you can easily manage a node in an OKD cluster through several tasks:

Enhancement operations

OKD allows you to do more than just access and manage nodes; as an administrator, you can perform the following tasks on nodes to make the cluster more efficient, application-friendly, and to provide a better environment for your developers.

About pods

A pod is one or more containers deployed together on a node. As a cluster administrator, you can define a pod, assign it to run on a healthy node that is ready for scheduling, and manage. A pod runs as long as the containers are running. You cannot change a pod once it is defined and is running. Some operations you can perform when working with pods are:

Read operations

As an administrator, you can get information about pods in a project through the following tasks:

Management operations

The following list of tasks provides an overview of how an administrator can manage pods in an OKD cluster.

Enhancement operations

You can work with pods more easily and efficiently with the help of various tools and features available in OKD. The following operations involve using those tools and features to better manage pods.

Operation User More information

Create and use a horizontal pod autoscaler.

Developer

You can use a horizontal pod autoscaler to specify the minimum and the maximum number of pods you want to run, as well as the CPU utilization or memory utilization your pods should target. Using a horizontal pod autoscaler, you can automatically scale pods.

Install and use a vertical pod autoscaler.

Administrator and developer

As an administrator, use a vertical pod autoscaler to better use cluster resources by monitoring the resources and the resource requirements of workloads.

As a developer, use a vertical pod autoscaler to ensure your pods stay up during periods of high demand by scheduling pods to nodes that have enough resources for each pod.

Provide access to external resources using device plug-ins.

Administrator

A device plug-in is a gRPC service running on nodes (external to the kubelet), which manages specific hardware resources. You can deploy a device plug-in to provide a consistent and portable solution to consume hardware devices across clusters.

Provide sensitive data to pods using the Secret object.

Administrator

Some applications need sensitive information, such as passwords and usernames. You can use the Secret object to provide such information to an application pod.

About containers

A container is the basic unit of an OKD application, which comprises the application code packaged along with its dependencies, libraries, and binaries. Containers provide consistency across environments and multiple deployment targets: physical servers, virtual machines (VMs), and private or public cloud.

Linux container technologies are lightweight mechanisms for isolating running processes and limiting access to only designated resources. As an administrator, You can perform various tasks on a Linux container, such as:

OKD provides specialized containers called Init containers. Init containers run before application containers and can contain utilities or setup scripts not present in an application image. You can use an Init container to perform tasks before the rest of a pod is deployed.

Apart from performing specific tasks on nodes, pods, and containers, you can work with the overall OKD cluster to keep the cluster efficient and the application pods highly available.

Common terms

This glossary defines common terms that are used in the node content. These terms help you understand nodes effectively.

Container

It is a lightweight and executable image that comprises software and all its dependencies. Containers virtualize the operating system, as a result, you can run containers anywhere from a data center to a public or private cloud to even a developer’s laptop.

Daemon set

Ensures that a replica of the pod runs on eligible nodes in an OKD cluster.

egress

The process of data sharing externally through a network’s outbound traffic from a pod.

garbage collection

The process of cleaning up cluster resources, such as terminated containers and images that are not referenced by any running pods.

Horizontal Pod Autoscaler(HPA)

Implemented as a Kubernetes API resource and a controller. You can use the HPA to specify the minimum and maximum number of pods that you want to run. You can also specify the CPU or memory utilization that your pods should target. The HPA scales out and scales in pods when a given CPU or memory threshold is crossed.

Ingress

Incoming traffic to a pod.

Job

A process that runs to completion. A job creates one or more pod objects and ensures that the specified pods are successfully completed.

Labels

You can use labels, which are key-value pairs, to organise and select subsets of objects, such as a pod.

Node

A worker machine in the OKD cluster. A node can be either be a virtual machine (VM) or a physical machine.

Node Tuning Operator

You can use the Node Tuning Operator to manage node-level tuning by using the TuneD daemon. It ensures custom tuning specifications are passed to all containerized TuneD daemons running in the cluster in the format that the daemons understand. The daemons run on all nodes in the cluster, one per node.

Self Node Remediation Operator

The Operator runs on the cluster nodes and identifies and reboots nodes that are unhealthy.

Pod

One or more containers with shared resources, such as volume and IP addresses, running in your OKD cluster. A pod is the smallest compute unit defined, deployed, and managed.

Toleration

Indicates that the pod is allowed (but not required) to be scheduled on nodes or node groups with matching taints. You can use tolerations to enable the scheduler to schedule pods with matching taints.

Taint

A core object that comprises a key,value, and effect. Taints and tolerations work together to ensure that pods are not scheduled on irrelevant nodes.