If you are not familiar with the oc command, refer to OpenShift - Getting Started with the oc command.

An image contains the code used to create a deployment. Then, a deployment can be created from an image, which should then create a replica set (which is the number of pods that should be created), and then the pods should be created.

Replicas is the number of pods that should be created for the deployment.

When deploying an application using the oc new-app command, if the --as-deployment-config flag is not used, the application will be created as a deployment, not a deployment config. In this scenario, a replica set will be used to create the pods.

If the --as-deployment-config flag is used, the application will be created as a deployment config. In this scenario, a replication controller will be used to create the pods.

The oc get deploymentconfigs command can be used to view the applications that have been deployed using the --as-deployment-config flag.

~]$ oc get deploymentconfigs
NAME      REVISION   DESIRED   CURRENT   TRIGGERED BY
my-app    1          1         1         config,image(my-app:latest)

The oc get replicationcontrollers (or oc get rc) command can be used to list the replication controllers. In this example, the deployment config has 1 replica which means that 1 pod should be created for the deployment.

~]$ oc get rc
NAME       DESIRED   CURRENT   READY   AGE
my-app-1   1         1         1       42s

Here is a sample YAML that could be used to create a replication controller.

apiVersion: v1
kind: ReplicationController
metadata:
  name: my-replication-controller
  namespace: my-project
spec:
  replicas: 2
  selector:
    app: my-app
  template:
    metadata:
      name: my-app
      labels:
        app: my-app
    spec:
      containers:
        - name: my-app
          image: >-
            image-registry.openshift-image-registry.svc:5000/openshift/my-app:latest
          ports:
            - containerPort: 8080

The oc get pods command can be used to display the pods. In this example, as expected, one pod was created for the deployment config.

~]# oc get pods
NAME                       READY   STATUS     RESTARTS  AGE
my-app-5b9879db6d-9mzm2    1/1     Running    0         8d