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DevOps Tools - OpenShift


What is OpenShift?

OpenShift is a family of containerization software developed by Red Hat. Its flagship product is the OpenShift Container Platform—an on-premises platform as a service built around Docker containers orchestrated and managed by Kubernetes on a foundation of Red Hat Enterprise Linux. The family's other products provide this platform through different environments: Origin Community Distribution (OKD) serves as the community-driven upstream (akin to CentOS), OpenShift Online is the platform offered as software as a service, and Openshift Dedicated is the platform offered as a managed service. 


OpenShift originally came from Red Hat's acquisition of Makara - a company with a proprietary PaaS solution based on Linux containers. Even though OpenShift was announced in May 2011, it was proprietary technology and did not become open-source until May of 2012. Up until v3, the container technology and container orchestration technology used custom developed technologies. This changed in v3 with the adoption of Docker as the container technology, and Kubernetes as the container orchestration technology. The v4 product has many other architectural changes - a prominent one being a shift to using CRIO as the container runtime, and Buildah as the container build tool, thus breaking the exclusive dependency on Docker. 

OpenShift Architecture

The main differentiator between OpenShift and vanilla Kubernetes is the notion of build related artifacts being first class Kubernetes resources upon which standard Kubernetes operations can apply. The OpenShift client program is "oc" - which offers a superset of capabilities offered by the "kubectl" client program of Kubernetes. Using this client, one can directly interact with the build related resources using sub-commands (such as "new-build" or "start-build"). In addition to this, an OpenShift-native pod build technology called Source-to-Image (S2I) is available out of the box. For the OpenShift platform, this provides capabilities equivalent to what Jenkins can do.

Some other differences when OpenShift is compared to Kubernetes:

  1. The v4 product line uses the CRI-O runtime - which means that docker daemons are not present on the master or worker nodes. This improves the security posture of the cluster.
  2. The out-of-the-box install of OpenShift comes included with an image repository.
  3. ImageStreams (a sequence of pointers to images which can be associated with deployments) and Templates (a packaging mechanism for application components) are unique to OpenShift and simplify application deployment and management.
  4. The "new-app" command which can be used to initiate an application deployment automatically applies the app label (with the value of the label taken from the --name argument) to all resources created as a result of the deployment. This can simplify the management of application resources.


OpenShift Products

OpenShift Container Platform

OpenShift Container Platform (formerly known as OpenShift Enterprise is Red Hat's on-premises private platform as a service product, built around a core of application containers powered by Docker, with orchestration and management provided by Kubernetes, on a foundation of Red Hat Enterprise Linux and Red Hat Enterprise Linux CoreOS (RHCOS).

OpenShift Origin

OpenShift Origin, also known since August 2018 as OKD (Origin Community Distribution) is the upstream community project used in OpenShift Online, OpenShift Dedicated, and OpenShift Container Platform. Built around a core of Docker container packaging and Kubernetes container cluster management, Origin is augmented by application lifecycle management functionality and DevOps tooling. Origin provides an open source application container platform. All source code for the Origin project is available under the Apache License (Version 2.0) on GitHub.

Red Hat OpenShift Online

Red Hat OpenShift Online (RHOO) is Red Hat's public cloud application development and hosting service which runs on AWS.

Online offered version 2 of the Origin project source code, which is also available under the Apache License Version 2.0. This version supported a variety of languages, frameworks, and databases via pre-built "cartridges" running under resource-quota "gears". Developers could add other language, database, or components via the OpenShift Cartridge application programming interface. This was deprecated in favour of OpenShift 3 and was withdrawn on 30 September 2017 for non-paying customers and 31 December 2017 for paying customers.

OpenShift 3 is built around Kubernetes. It can run any Docker-based container, but Openshift Online is limited to running containers that do not require root.

OpenShift Dedicated

OpenShift Dedicated is Red Hat's managed private cluster offering, built around a core of application containers powered by Docker, with orchestration and management provided by Kubernetes, on a foundation of Red Hat Enterprise Linux. It is available on the Amazon Web Services (AWS), Google Cloud Platform (GCP) and Microsoft Azure marketplaces since December 2016. 

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