OpenShift Tutorial

OpenShift is a Kubernetes-based container platform developed by Red Hat. It provides a set of tools and services designed to help developers build, deploy, and manage applications in a cloud-native environment. Here are some key features of OpenShift:

1.     Container Orchestration: At its core, OpenShift uses Kubernetes for container orchestration, which means it helps manage the deployment, scaling, and operation of containerized applications.

2.     Developer Tools: OpenShift includes a variety of tools to simplify the development process, such as integrated CI/CD pipelines, source-to-image (S2I) builds, and application templates.

3.     Operator Framework: It uses operators to manage complex applications and their lifecycle, making it easier to deploy and maintain applications with specific operational needs.

4.     Multi-Cloud and Hybrid Cloud: OpenShift supports deployment across different cloud environments (public, private, and hybrid) and on-premises infrastructure.

5.     Security and Compliance: It comes with built-in security features like role-based access control (RBAC), security context constraints (SCCs), and network policies to help ensure secure application deployment and management.

6.     User Experience: OpenShift offers a web-based console and CLI tools that provide a user-friendly experience for managing applications and clusters.

7.     Networking and Storage: It includes features for managing networking and storage, integrating with various networking plugins and storage solutions.

 

OpenShift’s Architecture

OpenShift’s architecture is designed to facilitate the deployment, management, and scaling of containerized applications. It is built on top of Kubernetes and integrates various components to enhance its functionality and ease of use. Here’s a high-level overview of the key components and their roles in OpenShift's architecture:

1. Control Plane

• Master Nodes: The control plane consists of master nodes responsible for managing the Kubernetes cluster. They handle tasks such as scheduling, API requests, and managing the overall state of the cluster. Key components include:
• API Server: Exposes the Kubernetes API and serves as the entry point for all administrative tasks.
• Scheduler: Determines which node should run a given pod based on resource requirements and other factors.
• Controller Manager: Ensures that the desired state of the cluster is maintained by running controllers that handle various aspects of the cluster (e.g., replication, deployments).
• etcd: A distributed key-value store that holds the cluster's state and configuration data.

2. Worker Nodes

• Nodes: These are the machines (physical or virtual) that run the containerized applications. Each node has:
• Kubelet: An agent that runs on each node, ensuring that containers are running in a pod.
• Kube Proxy: Maintains network rules on nodes, enabling communication between pods and services.
• Container Runtime: The software responsible for running containers, such as Docker or containerd.

3. OpenShift-Specific Components

• OpenShift API Server: Extends the Kubernetes API to include OpenShift-specific features and resources, such as builds and image streams.
• OpenShift Controller Manager: Manages OpenShift-specific resources and functions, including deployments and application lifecycle management.
• Router: Provides external access to services and applications running within the cluster. It typically uses HTTP or HTTPS and implements load balancing and routing rules.
• Registry: A built-in container image registry for storing and managing container images. OpenShift provides an integrated solution for storing and accessing container images used in the cluster.
• Service Catalog: Provides access to external services and integrates them into the OpenShift environment. This is useful for provisioning and managing external services like databases or message brokers.

4. Additional Components

• Developer and Operations Tools:
• Web Console: A graphical interface for managing and monitoring the OpenShift cluster and applications.
• CLI Tools: The oc command-line tool for interacting with the OpenShift cluster and performing administrative tasks.
• CI/CD Pipelines: Integrated tools for continuous integration and continuous deployment, enabling automated builds, tests, and deployments.

5. Networking and Storage

• Networking: OpenShift provides networking solutions for managing communication between pods, services, and external clients. This includes DNS, service discovery, and network policies.
• Storage: OpenShift supports various storage solutions for persistent data, including local storage, networked storage (e.g., NFS), and cloud-based storage services.

6. Security

• Security Context Constraints (SCCs): Define permissions and access controls for containers running within the cluster.
• Role-Based Access Control (RBAC): Manages permissions and access to cluster resources based on roles assigned to users and groups.

Overall, OpenShift's architecture combines Kubernetes' powerful orchestration capabilities with additional features and tools to support enterprise-grade application development and management. It integrates various components to provide a comprehensive platform for running containerized applications efficiently and securely.

 OpenShift Commands

Here are some commonly used oc commands in OpenShift that can help you manage and interact with your OpenShift cluster:

Basic Commands

1.     Login and Logout

• oc login <URL> --token=<token>: Log in to an OpenShift cluster using a token.
• oc logout: Log out from the current OpenShift cluster session.

2.     Get Information

• oc status: Display a summary of the current project and cluster status.
• oc whoami: Show information about the current user.
• oc get nodes: List all nodes in the cluster.
• oc get pods: List all pods in the current namespace.
• oc get services: List all services in the current namespace.
• oc get deployments: List all deployments in the current namespace.
• oc get projects: List all projects (namespaces) in the cluster.

3.     Describe Resources

• oc describe pod <pod-name>: Show detailed information about a specific pod.
• oc describe service <service-name>: Show detailed information about a specific service.
• oc describe deployment <deployment-name>: Show detailed information about a specific deployment.

4.     Logs and Debugging

• oc logs <pod-name>: Fetch logs from a specific pod.
• oc exec -it <pod-name> -- /bin/bash: Start a shell session inside a container of a specific pod.

Resource Management

1.     Creating and Deleting Resources

• oc create -f <filename>.yaml: Create resources from a YAML or JSON file.
• oc delete -f <filename>.yaml: Delete resources defined in a YAML or JSON file.
• oc create namespace <namespace-name>: Create a new namespace.
• oc delete namespace <namespace-name>: Delete a namespace and its resources.

2.     Updating Resources

• oc apply -f <filename>.yaml: Apply changes to resources defined in a YAML or JSON file.
• oc patch <resource-type> <resource-name> -p '{"spec": {"key": "value"}}': Apply a partial update to a resource.

Applications and Builds

1.     Deployments

• oc new-app <image-name>: Create a new application from a container image.
• oc expose deployment <deployment-name>: Create a service to expose a deployment.
• oc rollout status deployment/<deployment-name>: Check the status of a rollout for a deployment.
• oc scale deployment <deployment-name> --replicas=<number>: Scale the number of replicas for a deployment.

2.     Builds

• oc new-build <image-name>: Create a new build configuration from a container image.
• oc start-build <build-name>: Start a new build manually.
• oc get builds: List all builds.

Configuration and Secrets

1.     ConfigMaps and Secrets

• oc create configmap <configmap-name> --from-literal=<key>=<value>: Create a ConfigMap from literal values.
• oc create secret generic <secret-name> --from-literal=<key>=<value>: Create a secret from literal values.
• oc get configmaps: List all ConfigMaps in the current namespace.
• oc get secrets: List all secrets in the current namespace.

2.     Environment Variables

• oc set env deployment/<deployment-name> <key>=<value>: Set environment variables for a deployment.
• oc set image deployment/<deployment-name> <container-name>=<image>: Update the image for a deployment.

Projects and Context

1.     Namespace Management

• oc project <project-name>: Switch to a different project (namespace).
• oc new-project <project-name>: Create a new project.

2.     Context Management

• oc config view: View the current Kubernetes configuration.
• oc config use-context <context-name>: Switch between different contexts in your Kubernetes configuration.

Advanced Commands

1.     Resource Quotas and Limits

• oc get quota: List resource quotas in the current namespace.
• oc describe quota <quota-name>: Show detailed information about a specific resource quota.

2.     Network and Services

• oc get routes: List all routes in the current namespace.
• oc describe route <route-name>: Show detailed information about a specific route.

These commands cover a broad range of tasks, from basic cluster management to more advanced application deployment and troubleshooting. You can combine and tailor them based on your specific needs and the structure of your OpenShift environment.