Red Hat SummitChapter 6. Glossary of common terms for OpenShift Container Platform
This glossary defines common Kubernetes and OpenShift Container Platform terms.
- access policies
- A set of roles that dictate how users, applications, and entities within a cluster interact with one another. An access policy increases cluster security.
- admission plugins
- Admission plugins enforce security policies, resource limitations, or configuration requirements.
- authentication
- To control access to an OpenShift Container Platform cluster, a cluster administrator can configure user authentication to ensure only approved users access the cluster. To interact with an OpenShift Container Platform cluster, you must authenticate with the OpenShift Container Platform API. You can authenticate by providing an OAuth access token or an X.509 client certificate in your requests to the OpenShift Container Platform API.
- bootstrap
- A temporary machine that runs minimal Kubernetes and deploys the OpenShift Container Platform control plane.
- build
- A build is the process of transforming input parameters, such as source code, into a runnable container image. This process is defined by a BuildConfig object, which specifies the entire build workflow. OpenShift Container Platform utilizes Kubernetes to create containers from the build images and push them to the integrated container registry.
- certificate signing requests (CSRs)
- A resource requests a denoted signer to sign a certificate. This request might get approved or denied.
- Cluster Version Operator (CVO)
- An Operator that checks with the OpenShift Container Platform Update Service to see the valid updates and update paths based on current component versions and information in the graph.
- compute nodes
- Nodes that are responsible for executing workloads for cluster users.
- configuration drift
- A situation where the configuration on a node does not match what the machine config specifies.
- container
- Container is a lightweight, portable application instance that runs in OCI-compliant environments on compute nodes. Each container is a runtime instance of an Open Container Initiative (OCI)-compliant image, which is a binary package containing the application and its dependencies. A single compute node can host multiple containers, with its capacity determined by the memory and CPU resources available, whether on cloud infrastructure, physical hardware, or virtualized environments.
- container orchestration engine
- Software that automates the deployment, management, scaling, and networking of containers.
- container workloads
- Applications that are packaged and deployed in containers.
- control groups (cgroups)
- Partitions sets of processes into groups to manage and limit the resources processes consume.
- control plane
- A container orchestration layer that exposes the API and interfaces to define, deploy, and manage the life cycle of containers. Control planes are also known as control plane machines.
- CRI-O
- A Kubernetes native container runtime implementation that integrates with the operating system to deliver an efficient Kubernetes experience.
- Deployment and DeploymentConfig
OpenShift Container Platform supports both Kubernetes Deployment objects and OpenShift Container Platform DeploymentConfig objects for managing application rollout and scaling.
A Deployment object defines how an application is deployed as pods. It specifies the container image to pull from the registry, the number of replicas to maintain, and the labels that guide scheduling onto compute nodes. The Deployment creates and manages a ReplicaSet, which ensures the specified number of pods are running. Additionally, Deployment objects support various rollout strategies to update pods while maintaining application availability.
A DeploymentConfig object extends Deployment functionality by introducing change triggers, which automatically create new deployment versions when a new container image version becomes available or when other defined changes occur. This enables automated rollout management within OpenShift Container Platform.
- Dockerfile
- A text file that contains the user commands to perform on a terminal to assemble the image.
- hosted control planes
A OpenShift Container Platform feature that enables hosting a control plane on the OpenShift Container Platform cluster from its data plane and workers. This model performs the following actions:
- Optimize infrastructure costs required for the control planes.
- Improve the cluster creation time.
- Enable hosting the control plane using the Kubernetes native high level primitives. For example, deployments and stateful sets.
- Allow a strong network segmentation between the control plane and workloads.
- hybrid cloud deployments
- Deployments that deliver a consistent platform across bare metal, virtual, private, and public cloud environments. This offers speed, agility, and portability.
- Ignition
- A utility that RHCOS uses to manipulate disks during initial configuration. It completes common disk tasks, including partitioning disks, formatting partitions, writing files, and configuring users.
- installer-provisioned infrastructure
- The installation program deploys and configures the infrastructure that the cluster runs on.
- kubelet
- A primary node agent that runs on each node in the cluster to ensure that containers are running in a pod.
- Kubernetes
- Kubernetes is an open source container orchestration engine for automating deployment, scaling, and management of containerized applications.
- kubernetes manifest
- Specifications of a Kubernetes API object in a JSON or YAML format. A configuration file can include deployments, config maps, secrets, daemon sets.
- Machine Config Daemon (MCD)
- A daemon that regularly checks the nodes for configuration drift.
- Machine Config Operator (MCO)
- An Operator that applies the new configuration to your cluster machines.
- machine config pools (MCP)
- A group of machines, such as control plane components or user workloads, that are based on the resources that they handle.
- metadata
- Additional information about cluster deployment artifacts.
- microservices
- An approach to writing software. Applications can be separated into the smallest components, independent from each other by using microservices.
- mirror registry
- A registry that holds the mirror of OpenShift Container Platform images.
- monolithic applications
- Applications that are self-contained, built, and packaged as a single piece.
- namespaces
- A namespace isolates specific system resources that are visible to all processes. Inside a namespace, only processes that are members of that namespace can see those resources.
- networking
- Network information of OpenShift Container Platform cluster.
- node
- A compute machine in the OpenShift Container Platform cluster. A node is either a virtual machine (VM) or a physical machine.
- OpenShift CLI (
oc) - A command line tool to run OpenShift Container Platform commands on the terminal.
- OpenShift Dedicated
- A managed RHEL OpenShift Container Platform offering on Amazon Web Services (AWS) and Google Cloud Platform (GCP). OpenShift Dedicated focuses on building and scaling applications.
- OpenShift Update Service (OSUS)
- For clusters with internet access, Red Hat Enterprise Linux (RHEL) provides over-the-air updates by using an OpenShift update service as a hosted service located behind public APIs.
- OpenShift image registry
- A registry provided by OpenShift Container Platform to manage images.
- Operator
The preferred method of packaging, deploying, and managing a Kubernetes application in an OpenShift Container Platform cluster. An Operator is a Kubernetes-native application designed to translate operational knowledge into a software that is packaged and shared with customers. Traditionally, tasks such as installation, configuration, scaling, updates, and failover were managed manually by administrators by using scripts or automation tools like Ansible. Operators bring these capabilities into Kubernetes, making them natively integrated and automated within the cluster.
Operators manage both Day 1 operations such as installation and configuration, and Day 2 operations such as scaling, updates, backups, failover and restores. By leveraging Kubernetes APIs and concepts, Operators provide an automated and consistent way to manage complex applications.
- OperatorHub
- A platform that contains various OpenShift Container Platform Operators to install.
- Operator Lifecycle Manager (OLM)
- OLM helps you to install, update, and manage the lifecycle of Kubernetes native applications. OLM is an open source toolkit designed to manage Operators in an effective, automated, and scalable way.
- OSTree
- An upgrade system for Linux-based operating systems that performs atomic upgrades of complete file system trees. OSTree tracks meaningful changes to the file system tree using an addressable object store, and is designed to complement existing package management systems.
- over-the-air (OTA) updates
- The OpenShift Container Platform Update Service (OSUS) provides over-the-air updates to OpenShift Container Platform, including Red Hat Enterprise Linux CoreOS (RHCOS).
- pod
- A pod is one or more containers deployed together on one host. It consists of a colocated group of containers with shared resources such as volumes and IP addresses. A pod is also the smallest compute unit defined, deployed, and managed. In OpenShift Container Platform, pods replace individual application containers as the smallest deployable unit. Pods are the orchestrated unit in OpenShift Container Platform. OpenShift Container Platform schedules and runs all containers in a pod on the same node. Complex applications are made up of multiple pods, each with their own containers. They interact externally and also with another inside the OpenShift Container Platform environment.
- private registry
- OpenShift Container Platform can use any server implementing the container image registry API as a source of the image which helps the developers to push and pull their private container images.
- project
OpenShift Container Platform uses projects to enable groups of users or developers to work together. A project defines the scope of resources, manages user access, and enforces resource quotas and limits.
A project is a Kubernetes namespace with additional annotations that provide role-based access control (RBAC) and management capabilities. It serves as the central mechanism for organizing resources, ensuring isolation between different user groups.
- public registry
- OpenShift Container Platform can use any server implementing the container image registry API as a source of the image which allows the developers to push and pull their public container images.
- RHEL OpenShift Container Platform Cluster Manager
- A managed service where you can install, modify, operate, and upgrade your OpenShift Container Platform clusters.
- RHEL Quay Container Registry
- A Quay.io container registry that serves most of the container images and Operators to OpenShift Container Platform clusters.
- replication controllers
- An asset that indicates how many pod replicas are required to run at a time.
- ReplicaSet and ReplicationController
-
The Kubernetes
ReplicaSetandReplicationControllerobjects ensure that the desired number of pod replicas are running at all times. If a pod fails, exits, or is deleted, these controllers automatically create new pods to maintain the specified replica count. Conversely, if there are more pods than required, the ReplicaSet or ReplicationController scales down by terminating excess pods to match the defined replica count. - role-based access control (RBAC)
- A key security control to ensure that cluster users and workloads have only access to resources required to execute their roles.
- route
- A route is a way to expose a service by giving it an externally reachable hostname, such as www.example.com. Each route consists of a route name, a service selector, and optionally, a security configuration.
- router
- A router processes defined routes and their associated service endpoints, enabling external clients to access applications. While deploying a multi-tier application in OpenShift Container Platform is straightforward, external traffic cannot reach the application without the routing layer.
- scaling
- The increasing or decreasing of resource capacity.
- service
- A service in OpenShift Container Platform defines a logical set of pods and the access policies for reaching them. It provides a stable internal IP address and hostname, ensuring seamless communication between application components as pods are created and destroyed.
- Source-to-Image (S2I) image
- An image created based on the programming language of the application source code in OpenShift Container Platform to deploy applications.
- storage
- OpenShift Container Platform supports many types of storage, both for on-premise and cloud providers. You can manage container storage for persistent and non-persistent data in an OpenShift Container Platform cluster.
- telemetry
- A component to collect information such as size, health, and status of OpenShift Container Platform.
- template
- A template describes a set of objects that can be parameterized and processed to produce a list of objects for creation by OpenShift Container Platform.
- user-provisioned infrastructure
- You can install OpenShift Container Platform on the infrastructure that you provide. You can use the installation program to generate the assets required to provision the cluster infrastructure, create the cluster infrastructure, and then deploy the cluster to the infrastructure that you provided.
- web console
- A user interface (UI) to manage OpenShift Container Platform.
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