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OpenShift Cheat Sheet

A comprehensive cheat sheet covering essential OpenShift commands, concepts, and configurations for developers and operators.

Core Concepts & Commands

Basic Concepts

Project (Namespace): A logical grouping of resources, like a Kubernetes namespace.
Pod: The smallest deployable unit, containing one or more containers.
Service: Exposes an application running on a set of Pods as a network service.
Route: Exposes a service to the outside world.
DeploymentConfig: Defines the desired state of your application deployments.
Image Stream: Manages container images and their tags.

Common `oc` Commands

oc login <openshift_url>

Log in to the OpenShift cluster.

oc new-project <project_name>

Create a new project (namespace).

oc project <project_name>

Switch to a specific project.

oc get pods

List all pods in the current project.

oc create -f <file.yaml>

Create resources from a YAML file.

oc apply -f <file.yaml>

Apply changes to resources defined in a YAML file.

Resource Management

oc describe <resource_type> <resource_name>

Get detailed information about a resource.

oc delete <resource_type> <resource_name>

Delete a resource.

oc edit <resource_type> <resource_name>

Edit a resource directly.

oc logs <pod_name>

View the logs of a pod.

oc exec -it <pod_name> -- <command>

Execute a command inside a pod. Example: oc exec -it my-pod -- bash

Deployments and Services

DeploymentConfig Basics

DeploymentConfigs manage application deployments. They define the desired state (number of replicas, container image, etc.) and automatically roll out updates.

Use oc new-app to quickly create a DeploymentConfig from a container image or Git repository.

Example creating DeploymentConfig from image:

oc new-app openshift/hello-openshift --name=my-app

Service Management

oc expose dc/<deployment_config_name>

Create a service to expose a DeploymentConfig.

oc get svc

List services in the current project.

oc describe svc/<service_name>

Get details about a service.

Scaling Applications

oc scale dc/<deployment_config_name> --replicas=<number>

Scale the number of replicas for a DeploymentConfig.

oc autoscale dc/<deployment_config_name> --min=<min_replicas> --max=<max_replicas>

Configure autoscaling for a DeploymentConfig.

Rolling Updates

OpenShift supports rolling updates to minimize downtime during deployments. When you update a DeploymentConfig, OpenShift automatically updates the application instances without interrupting service.

To trigger a new deployment after changing the DeploymentConfig, use:

oc rollout latest dc/<deployment_config_name>

Routes and Networking

Route Configuration

Routes expose services to external traffic. They define the hostnames and paths that external clients use to access your applications.

Use oc expose to quickly create a route for a service:

oc expose svc/<service_name> --hostname=<desired_hostname>

Route Management Commands

oc get routes

List routes in the current project.

oc describe route/<route_name>

Get details about a specific route.

oc delete route/<route_name>

Delete a route.

Securing Routes with TLS

You can secure routes using TLS certificates. OpenShift supports edge, passthrough, and re-encrypt TLS termination.

To configure TLS, you’ll need to create a secret containing your TLS certificate and key, and then reference that secret in your route definition.

Example of creating secret:

oc create secret tls my-tls-secret --cert=path/to/cert.pem --key=path/to/key.pem

Builds and Image Streams

Build Concepts

Builds transform source code into runnable container images. OpenShift supports different build strategies, including Docker, Source-to-Image (S2I), and custom builds.

BuildConfigs define how builds are executed.

Image Streams

Image Streams manage container image tags and provide a level of indirection between deployments and the underlying images. This allows you to update images without modifying your deployment configurations.

When a new image is pushed to the registry, OpenShift can automatically trigger new deployments based on the updated Image Stream tags.

Common Build Commands

oc new-build <git_repo_url> --name=<build_name>

Create a new build configuration from a Git repository (S2I).

oc start-build <build_name>

Start a build.

oc get builds

List builds in the current project.

oc logs build/<build_name>

View the logs of a build.

Working with Image Streams

oc import-image <image_name> --from=<registry_url>/<image_name> --confirm

Import an image from a registry into an Image Stream.

oc get imagestreams

List Image Streams in the current project.

oc describe imagestream/<imagestream_name>

Get details about an Image Stream.
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