Chapter 2. OpenShift Dedicated architecture
2.1. Introduction to OpenShift Dedicated
OpenShift Dedicated is a platform for developing and running containerized applications. It is designed to allow applications and the data centers that support them to expand from just a few machines and applications to thousands of machines that serve millions of clients.
With its foundation in Kubernetes, OpenShift Dedicated incorporates the same technology that serves as the engine for massive telecommunications, streaming video, gaming, banking, and other applications. Its implementation in open Red Hat technologies lets you extend your containerized applications beyond a single cloud to on-premise and multi-cloud environments.
2.1.1. About Kubernetes
Although container images and the containers that run from them are the primary building blocks for modern application development, to run them at scale requires a reliable and flexible distribution system. Kubernetes is the defacto standard for orchestrating containers.
Kubernetes is an open source container orchestration engine for automating deployment, scaling, and management of containerized applications. The general concept of Kubernetes is fairly simple:
- Start with one or more worker nodes to run the container workloads.
- Manage the deployment of those workloads from one or more control plane nodes.
- Wrap containers in a deployment unit called a pod. Using pods provides extra metadata with the container and offers the ability to group several containers in a single deployment entity.
- Create special kinds of assets. For example, services are represented by a set of pods and a policy that defines how they are accessed. This policy allows containers to connect to the services that they need even if they do not have the specific IP addresses for the services. Replication controllers are another special asset that indicates how many pod replicas are required to run at a time. You can use this capability to automatically scale your application to adapt to its current demand.
In only a few years, Kubernetes has seen massive cloud and on-premise adoption. The open source development model allows many people to extend Kubernetes by implementing different technologies for components such as networking, storage, and authentication.
2.1.2. The benefits of containerized applications
Using containerized applications offers many advantages over using traditional deployment methods. Where applications were once expected to be installed on operating systems that included all their dependencies, containers let an application carry their dependencies with them. Creating containerized applications offers many benefits.
2.1.2.1. Operating system benefits
Containers use small, dedicated Linux operating systems without a kernel. Their file system, networking, cgroups, process tables, and namespaces are separate from the host Linux system, but the containers can integrate with the hosts seamlessly when necessary. Being based on Linux allows containers to use all the advantages that come with the open source development model of rapid innovation.
Because each container uses a dedicated operating system, you can deploy applications that require conflicting software dependencies on the same host. Each container carries its own dependent software and manages its own interfaces, such as networking and file systems, so applications never need to compete for those assets.
2.1.2.2. Deployment and scaling benefits
If you employ rolling upgrades between major releases of your application, you can continuously improve your applications without downtime and still maintain compatibility with the current release.
You can also deploy and test a new version of an application alongside the existing version. If the container passes your tests, simply deploy more new containers and remove the old ones.
Since all the software dependencies for an application are resolved within the container itself, you can use a standardized operating system on each host in your data center. You do not need to configure a specific operating system for each application host. When your data center needs more capacity, you can deploy another generic host system.
Similarly, scaling containerized applications is simple. OpenShift Dedicated offers a simple, standard way of scaling any containerized service. For example, if you build applications as a set of microservices rather than large, monolithic applications, you can scale the individual microservices individually to meet demand. This capability allows you to scale only the required services instead of the entire application, which can allow you to meet application demands while using minimal resources.
2.1.3. OpenShift Dedicated overview
OpenShift Dedicated provides enterprise-ready enhancements to Kubernetes, including the following enhancements:
- Integrated Red Hat technology. Major components in OpenShift Dedicated come from Red Hat Enterprise Linux (RHEL) and related Red Hat technologies. OpenShift Dedicated benefits from the intense testing and certification initiatives for Red Hat’s enterprise quality software.
- Open source development model. Development is completed in the open, and the source code is available from public software repositories. This open collaboration fosters rapid innovation and development.
Although Kubernetes excels at managing your applications, it does not specify or manage platform-level requirements or deployment processes. Powerful and flexible platform management tools and processes are important benefits that OpenShift Dedicated 4 offers. The following sections describe some unique features and benefits of OpenShift Dedicated.
2.1.3.1. Custom operating system
OpenShift Dedicated uses Red Hat Enterprise Linux CoreOS (RHCOS) as the operating system for all control plane and worker nodes.
RHCOS includes:
- Ignition, which OpenShift Dedicated uses as a firstboot system configuration for initially bringing up and configuring machines.
- CRI-O, a Kubernetes native container runtime implementation that integrates closely with the operating system to deliver an efficient and optimized Kubernetes experience. CRI-O provides facilities for running, stopping, and restarting containers. It fully replaces the Docker Container Engine, which was used in OpenShift Dedicated 3.
- Kubelet, the primary node agent for Kubernetes that is responsible for launching and monitoring containers.
2.1.3.2. Simplified update process
Updating, or upgrading, OpenShift Dedicated is a simple, highly-automated process. Because OpenShift Dedicated completely controls the systems and services that run on each machine, including the operating system itself, from a central control plane, upgrades are designed to become automatic events.
2.1.3.3. Other key features
Operators are both the fundamental unit of the OpenShift Dedicated 4 code base and a convenient way to deploy applications and software components for your applications to use. In OpenShift Dedicated, Operators serve as the platform foundation and remove the need for manual upgrades of operating systems and control plane applications. OpenShift Dedicated Operators such as the Cluster Version Operator and Machine Config Operator allow simplified, cluster-wide management of those critical components.
Operator Lifecycle Manager (OLM) and the OperatorHub provide facilities for storing and distributing Operators to people developing and deploying applications.
The Red Hat Quay Container Registry is a Quay.io container registry that serves most of the container images and Operators to OpenShift Dedicated clusters. Quay.io is a public registry version of Red Hat Quay that stores millions of images and tags.
Other enhancements to Kubernetes in OpenShift Dedicated include improvements in software defined networking (SDN), authentication, log aggregation, monitoring, and routing. OpenShift Dedicated also offers a comprehensive web console and the custom OpenShift CLI (oc) interface.
