OpenShift: An Open-Source Container Application Platform

Overview of OpenShift

OpenShift is a powerful Platform as a Service (PaaS) that enables developers to build, deploy, and manage applications quickly and efficiently. It integrates with Docker and Kubernetes to provide a comprehensive container orchestration and management solution, offering several variations depending on your needs:

1. OpenShift Origin: The community-driven upstream project that is the foundation for OpenShift.
2. OpenShift Online: A public cloud service where you can develop, build, and deploy applications in a hosted environment.
3. OpenShift Dedicated: A private cloud offering managed by Red Hat.
4. OpenShift Enterprise: A robust and scalable enterprise version for on-premises deployment.

OpenShift Origin: A Deep Dive

OpenShift Origin builds on top of Docker and Kubernetes, adding tools that cater to both developers and operations teams. It accelerates the application lifecycle by providing:

• Docker: Docker is a tool designed to make it easier to create, deploy, and run applications by using containers. Containers are lightweight, portable, and run the same regardless of where they are deployed. They package up the application with all its dependencies, ensuring consistency across multiple development and production environments.
• Kubernetes (K8s): Kubernetes is an open-source platform designed for automating deployment, scaling, and operations of application containers. It organizes Docker containers into pods, manages their lifecycle, and scales them across a cluster of machines.
• Developer and Operational Tools: OpenShift provides tools like Source Code Management (SCM), pipelines for continuous integration/continuous deployment (CI/CD), a container registry, software-defined networking, APIs, and governance features that streamline the development process.

Installing and Starting OpenShift

To get started with OpenShift, you can follow the official installation guide available at OpenShift Documentation.

Steps to Install and Start OpenShift:

1. Download the minishift zip file from the official website.
2. Extract the contents and copy them to your C: drive.
3. Open a Command Prompt (cmd) and run the following command to start OpenShift with a VirtualBox driver:

   minishift.exe start --vm-driver virtualbox        

Accessing OpenShift

OpenShift can be accessed in three different ways:

1. REST API: For programmatic access, allowing you to interact with OpenShift programmatically via HTTP requests.
2. CLI (Command Line Interface): Provides a powerful way to interact with OpenShift using the oc command.
3. Web Console: A user-friendly graphical interface to manage your OpenShift resources.

Working with OpenShift CLI (oc)

The oc command-line client is a powerful tool for interacting with OpenShift. Below are some common commands and explanations:

• Set Up the Environment for oc:

  oc-env        

This command configures your shell environment for the oc client.

• Login as an Admin:

  oc login -u admin -p password        

This logs you in as an administrator.

• Login as a Developer:

  oc login -u developer -p password        

This logs you in as a developer user.

• Logout:

  oc logout        

This logs you out of your current OpenShift session.

• Check Current User:

  oc whoami -t        

This command returns the current user and authentication token being used.

• Manage Projects:

  oc get projects
  oc project dev-2        

The first command lists all projects you have access to. The second command switches to a specific project (dev-2).

• Rollout Management:

  oc rollout latest dc/simple-webapp-docker
  oc rollout history dc/simple-webapp-docker
  oc rollout describe dc/simple-webapp-docker
  oc rollout undo dc/simple-webapp-docker        

These commands are used for managing deployments, including initiating a rollout, viewing the rollout history, describing the current state, and undoing the last deployment.

• Persistent Volume Claims (PVC):

  oc get pvc
  oc delete pvc db        

These commands allow you to manage persistent storage claims, which are used to store data persistently across pod restarts.

• Resource Creation and Management:

  oc create -f app.yml -n project-1
  oc export service db        

These commands create resources from a YAML configuration file and export services for easier replication.

Example: Starting and Managing Minishift

To work with Minishift, the following commands are useful:

• Start Minishift:

  minishift.exe start --vm-driver virtualbox        

This command starts the Minishift VM using VirtualBox as the driver.

• Set Up Environment for Minishift:

  minishift oc-env        

Configures your shell environment for the Minishift oc client.

• Delete Minishift VM:

  minishift delete        

Removes the Minishift VM and any associated data.

• Check Minishift Status:

  minishift status        

Displays the current status of the Minishift VM.

• Restart OpenShift:

  minishift openshift restart        

Restarts the OpenShift cluster running within Minishift.

Using REST API with OpenShift

The REST API is a powerful way to interact with OpenShift programmatically. For example, to get user information or list all projects:

• Get Current User:

  oc whoami -t
  curl https://locahost:8443/oapi/v1/users -H "Authorization: Bearer <Token>"        

• List All Projects:

  curl https://192.168.99.100:8443/oapi/v1/projects -k -H "Authorization: Bearer fbegqvmGfxVH-1yC2d74FStFXotypp6FO8o0sWtGOyI"        

Building and Deploying Applications

OpenShift supports multiple deployment strategies and provides robust CI/CD capabilities. Here’s how a typical deployment pipeline might look:

1. Source Code Repository: Code is stored in a version control system like Git.
2. Source to Image (S2I): OpenShift builds Docker images directly from the source code.
3. Docker Image Creation: The S2I process creates a Docker image.
4. Docker Registry: The image is pushed to a Docker registry.
5. Deployment: The application is deployed to the OpenShift cluster.

Deployment Strategies:

• Recreate: Stops the old version of the application before starting the new one.
• Blue/Green: Deploys a new version alongside the old one, and then switches traffic to the new version.
• Rolling: Gradually replaces old instances with new ones.