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Chapter 1. Overview of nodes
1.1. 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 Red Hat OpenShift Service on AWS, the control plane nodes contain more than just the Kubernetes services for managing the Red Hat OpenShift Service on AWS cluster.
Having stable and healthy nodes in a cluster is fundamental to the smooth functioning of your hosted application. In Red Hat OpenShift Service on AWS, 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.
The following components of a node are responsible for maintaining the running of pods and providing the Kubernetes runtime environment.
- Container runtime
- The container runtime is responsible for running containers. Kubernetes offers several runtimes such as containerd, cri-o, rktlet, and Docker.
- Kubelet
- Kubelet runs on nodes and reads the container manifests. It ensures that the defined containers have started and are running. The kubelet process maintains the state of work and the node server. Kubelet manages network rules and port forwarding. The kubelet manages containers that are created by Kubernetes only.
- Kube-proxy
- Kube-proxy runs on every node in the cluster and maintains the network traffic between the Kubernetes resources. A Kube-proxy ensures that the networking environment is isolated and accessible.
- DNS
- Cluster DNS is a DNS server which serves DNS records for Kubernetes services. Containers started by Kubernetes automatically include this DNS server in their DNS searches.
Read operations
The read operations allow an administrator or a developer to get information about nodes in an Red Hat OpenShift Service on AWS cluster.
- List all the nodes in a cluster.
- Get information about a node, such as memory and CPU usage, health, status, and age.
- List pods running on a node.
Enhancement operations
Red Hat OpenShift Service on AWS 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.
- Manage node-level tuning for high-performance applications that require some level of kernel tuning by using the Node Tuning Operator.
- Run background tasks on nodes automatically with daemon sets. You can create and use daemon sets to create shared storage, run a logging pod on every node, or deploy a monitoring agent on all nodes.
- Run background tasks on nodes automatically with daemon sets. You can create and use daemon sets to create shared storage, run a logging pod on every node, or deploy a monitoring agent on all nodes.
1.2. 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:
- List pods associated with a project, including information such as the number of replicas and restarts, current status, and age.
- View pod usage statistics such as CPU, memory, and storage consumption.
Management operations
The following list of tasks provides an overview of how an administrator can manage pods in an Red Hat OpenShift Service on AWS cluster.
Control scheduling of pods using the advanced scheduling features available in Red Hat OpenShift Service on AWS:
- Node-to-pod binding rules such as pod affinity, node affinity, and anti-affinity.
- Node labels and selectors.
- Pod topology spread constraints.
- Configure how pods behave after a restart using pod controllers and restart policies.
- Limit both egress and ingress traffic on a pod.
- Add and remove volumes to and from any object that has a pod template. A volume is a mounted file system available to all the containers in a pod. Container storage is ephemeral; you can use volumes to persist container data.
Enhancement operations
You can work with pods more easily and efficiently with the help of various tools and features available in Red Hat OpenShift Service on AWS. The following operations involve using those tools and features to better manage pods.
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Secrets: Some applications need sensitive information, such as passwords and usernames. An administrator can use the
Secretobject to provide sensitive data to pods using theSecretobject.
1.3. About containers
A container is the basic unit of an Red Hat OpenShift Service on AWS 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:
Red Hat OpenShift Service on AWS 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 Red Hat OpenShift Service on AWS cluster to keep the cluster efficient and the application pods highly available.
1.4. Glossary of common terms for Red Hat OpenShift Service on AWS nodes
This glossary defines common terms that are used in the node content.
- 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 Red Hat OpenShift Service on AWS 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.
- 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 Red Hat OpenShift Service on AWS 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 Red Hat OpenShift Service on AWS 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.
