100+ Free EX342 Practice Questions

Explanation: `oc new-app <git-url>` creates all necessary resources to build and deploy an application from source using S2I. OpenShift detects the language, selects an appropriate builder image, creates a BuildConfig, a DeploymentConfig (or Deployment), an ImageStream, and a Service. It is the primary command for getting new applications onto a cluster from source.

Explanation: `oc expose deployment/frontend --port=80` creates a ClusterIP Service and an HTTP Route for the deployment in one command. OpenShift automatically assigns a hostname based on the project name and cluster wildcard DNS. The `oc expose` command simplifies what would otherwise require separate `oc create service` and `oc create route` steps.

Explanation: A `BuildConfig` defines how OpenShift builds container images. It specifies the build strategy (S2I, Docker, or Custom), the source (Git, binary, Dockerfile), the output ImageStream tag, and triggers. Triggers can be configured to fire builds automatically when the source code changes (via webhooks) or when the base builder image is updated.

Explanation: `oc start-build myapp --follow` starts a new build and streams the log output. To view logs for an existing build without starting a new one, use `oc logs build/myapp-1`. The `--follow` flag streams the build log in real time until the build completes or fails.

Explanation: Using `valueFrom.configMapKeyRef` in the container's `env` section injects a specific ConfigMap key as an environment variable. The YAML snippet uses `name: DB_URL` for the env var and `valueFrom.configMapKeyRef: {name: app-config, key: database.url}`. This is the standard Kubernetes/OpenShift pattern for injecting individual config values as environment variables.

Explanation: A `Secret` stores sensitive data in base64-encoded form. It is important to note that base64 is encoding, not encryption — Secrets are not encrypted at rest by default unless etcd encryption is enabled. Secrets can be mounted as files or injected as environment variables into containers.

Explanation: An `ImageStream` is an OpenShift abstraction that tracks container images by tag, decoupling the image reference from the actual registry URL. When an ImageStreamTag is updated (by a build, import, or tag), deployments referencing it can be triggered to automatically roll out. This enables CI/CD pipelines where a new build automatically triggers a deployment.

Explanation: `oc create pvc` with `--storage-class` and `--size` creates a PersistentVolumeClaim. Alternatively, you can apply a YAML manifest with `apiVersion: v1, kind: PersistentVolumeClaim`. The PVC requests dynamic provisioning from the `standard` StorageClass for 5Gi of storage. The actual PersistentVolume is provisioned by the storage backend.

Explanation: `ImagePullBackOff` occurs when OpenShift fails to pull the container image from the registry. Common causes include: incorrect image name or tag, the image does not exist in the specified registry, missing or incorrect registry credentials (Secret not linked to ServiceAccount), or the registry is unreachable from the cluster.

Explanation: `oc scale deployment/backend --replicas=5` changes the desired replica count for the named Deployment. OpenShift immediately begins creating or terminating pods to reach the target count. This works with Deployment, DeploymentConfig, ReplicaSet, StatefulSet, and Job resources.