OpenShift Fundamentals
OpenShift is Red Hat's Kubernetes-based application platform. It combines container orchestration with integrated tools for building, exposing, securing, updating, and operating applications across datacenters and public clouds.
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Intro
OpenShift Fundamentals
OpenShift is a Kubernetes-based application platform from Red Hat. Kubernetes supplies the API, scheduler, controllers, and workload resources that keep containers running across a cluster. OpenShift adds an integrated operating system, cluster lifecycle automation, developer workflows, security controls, a web console, and supported platform services.
That distinction matters. Kubernetes coordinates containerized workloads, but it does not define a complete application platform. OpenShift assembles Kubernetes with tested components and manages much of the assembly as one release. Teams can run the platform on their own infrastructure or consume a managed OpenShift service from a cloud provider.
The cluster architecture
An OpenShift cluster has a control plane and compute nodes. Control-plane machines run the Kubernetes API server, scheduler, controllers, and the etcd key-value store. Compute nodes run application pods. Each node uses the kubelet to communicate with the control plane and CRI-O to run containers.
OpenShift Container Platform uses Red Hat Enterprise Linux CoreOS, or RHCOS, as its purpose-built node operating system. Ignition applies the initial machine configuration during first boot. The Machine Config Operator then manages operating-system and node configuration as declared cluster state.
Operators are controllers that encode operational knowledge. Cluster Operators manage platform components such as networking, authentication, monitoring, and the web console. The Cluster Version Operator coordinates platform updates. Operator Lifecycle Manager installs and updates optional applications packaged as Operators. These are related mechanisms, but they manage different lifecycles.
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Sources
- https://www.redhat.com/en/technologies/cloud-computing/openshift
Supports
- OpenShift portfolio, supported hybrid-cloud positioning, and consumption models
- Official product homepage used by the manifest and Landscape
- https://docs.redhat.com/en/documentation/openshift_container_platform/4.21/html-single/architecture/index
Supports
- OpenShift as a Kubernetes application platform and its control-plane and compute-node architecture
- RHCOS, Ignition, CRI-O, kubelet, Operators, CVO, MCO, OLM, console, oc, registry, and update architecture
- Pods, Services, Routes, installation methods, restricted networks, and platform limitations
- https://docs.redhat.com/en/documentation/openshift_container_platform/4.21/html/building_applications/index
Supports
- Application creation from source, images, manifests, Helm, and Operators
- Projects, Deployments, Services, application maintenance, and developer workflows
- Reference-path rationale for the building applications guide
- https://docs.redhat.com/en/documentation/openshift_container_platform/4.21/html/building_applications/projects
Supports
- Project creation, membership, roles, isolation, quotas, and system-project restrictions
- https://docs.redhat.com/en/documentation/openshift_container_platform/4.21/html-single/project_apis/project_apis
Supports
- Project as an alternative representation of a Kubernetes namespace
- Projects as units of isolation and collaboration rather than separate clusters
- https://docs.redhat.com/en/documentation/openshift_container_platform/4.21/html/network_apis/route-route-openshift-io-v1
Supports
- Route as public DNS and an HTTP or HTTPS aware proxy layer for Services
- Route TLS behavior and router-to-Service endpoint path
- https://docs.redhat.com/en/documentation/openshift_container_platform/4.21/html/images/index
Supports
- Image and image-stream reference behavior and the Images reference-path rationale
- Source-to-Image as a build process
- https://docs.redhat.com/en/documentation/openshift_container_platform/4.21/html/images/managing-image-streams
Supports
- Image streams as virtual views of related images rather than image data stores
- Image stream tags, change tracking, and build or deployment triggers
- https://docs.redhat.com/en/documentation/openshift_container_platform/4.21/html-single/updating_clusters/
Supports
- CVO, update service, channels, release image, Cluster Operator, and MCO update flow
- Update conditions, compatible Operators, failure behavior, and no supported rollback
- Reference-path rationale for the updating clusters guide
- https://docs.redhat.com/en/documentation/openshift_container_platform/4.21/html/updating_clusters/performing-a-cluster-update
Supports
- Backups, capacity, disruption budgets, machine config pools, and update preconditions
- Pod eviction and node-drain blockers during updates
- https://docs.redhat.com/en/documentation/openshift_container_platform/4.21/html/authentication_and_authorization/using-rbac
Supports
- Namespaced and cluster-wide roles, bindings, and least-scope authorization decisions
- https://docs.redhat.com/en/documentation/openshift_container_platform/4.21/html-single/security_apis/security_apis
Supports
- Security Context Constraints governing pod security-context requests
- https://docs.redhat.com/en/documentation/openshift_container_platform/4.21/html-single/tutorials/tutorials
Supports
- Guided project creation, image deployment, Service, and Route practice path
- Reference-path rationale for the tutorials
- https://github.com/sindresorhus/awesome
Supports
- Required discovery starting point and link to the curated Awesome Kubernetes list
- https://github.com/ramitsurana/awesome-kubernetes/wiki/Awesome---Kubernetes
Supports
- Curation presence of Helm, Kustomize, cert-manager, and K9s
- Awesome Links discovery decision
- https://helm.sh/docs/intro/introduction/
Supports
- Helm charts as versioned packages for defining, installing, upgrading, and rolling back Kubernetes applications
- Helm Awesome Link rationale
- https://kubernetes.io/docs/tasks/manage-kubernetes-objects/kustomization/
Supports
- Kustomize bases, overlays, generators, and manifest customization
- Kustomize Awesome Link rationale
- https://cert-manager.io/docs/
Supports
- Certificate resources, issuers, Secrets, and automated renewal on Kubernetes and OpenShift
- cert-manager Awesome Link rationale
- https://k9scli.io/topics/commands/
Supports
- K9s resource, namespace, context, log, and read-only inspection capabilities
- K9s Awesome Link rationale
- https://www.rancher.com/products/rancher-platform
Supports
- Rancher Prime cluster provisioning, import, centralized policy, monitoring, and multi-distribution management
- Rancher Prime placement and licensing model in Landscape
- https://www.vmware.com/products/app-platform/tanzu
Supports
- Tanzu Platform private-cloud application platform, code-to-deployment, and platform operations focus
- Tanzu placement in the OpenShift Landscape comparison
- https://cloud.google.com/kubernetes-engine/enterprise
Supports
- GKE Enterprise fleet, policy, and managed Kubernetes platform role
- GKE Enterprise placement in the OpenShift Landscape comparison
- https://aws.amazon.com/rosa/
Supports
- ROSA as a managed OpenShift service integrated with AWS accounts and services
- ROSA placement in Landscape
- https://azure.microsoft.com/products/openshift
Supports
- Azure Red Hat OpenShift as a jointly operated managed OpenShift service
- ARO placement in Landscape
- https://www.ibm.com/products/openshift
Supports
- Red Hat OpenShift on IBM Cloud as a managed OpenShift service
- IBM Cloud placement in Landscape
- https://www.redhat.com/en/about/press-releases/red-hat-launches-openshift-dedicated-delivering-its-container-application-platform-public-cloud-offering
Supports
- November 2011 OpenShift Online launch date and original hosted PaaS model
- December 2015 OpenShift Dedicated general availability and consumption models
- https://www.redhat.com/en/blog/Announcing-OpenShift-Origin-Open-Source-Code-For-Platform-as-a-Service
Supports
- April 30, 2012 Origin source release, Apache License version 2, and upstream purpose
- https://www.redhat.com/en/blog/red-hat-collaborates-with-open-source-community-to-deliver-innovative-platform-as-a-service
Supports
- March 2013 Origin upstream relationship, pull-request model, and public continuous integration
- https://www.redhat.com/en/blog/openshift-kubernetes-where-weve-been-and-where-were-going-part-1
Supports
- 2014 decision to standardize OpenShift on Kubernetes and June 2015 OpenShift 3 launch
- https://www.redhat.com/en/about/press-releases/red-hat-delivers-openshift-enterprise-3-power-new-web-scale-distributed-application-platform
Supports
- June 24, 2015 OpenShift Enterprise 3 general availability
- Combination of Docker-format containers, Kubernetes, and RHEL 7
- https://www.redhat.com/en/blog/red-hat-openshift-container-platform-4-now-defaults-cri-o-underlying-container-engine
Supports
- CRI-O technology preview in OpenShift 3.7, general availability in 3.9, and default in OpenShift 4
- https://www.redhat.com/en/about/press-releases/red-hat-unveils-roadmap-coreos-integration-red-hat-openshift
Supports
- January 2018 CoreOS acquisition and integration of Tectonic, Container Linux, Quay, and Operator work
- https://www.redhat.com/en/about/press-releases/red-hat-redefines-enterprise-kubernetes-through-full-stack-automation-red-hat-openshift-4
Supports
- May 8, 2019 OpenShift 4 introduction and Operator-based full-stack automated operations
- https://aws.amazon.com/about-aws/whats-new/2021/03/amazon-and-red-hat-announce-general-availability-rosa/
Supports
- March 24, 2021 ROSA general availability, OpenShift APIs, AWS integration, and service procurement