I al developing a Spring Boot application, I used docker-compose to create my containers. And for Kubernetes I used kompose via minikubes. I pushed my images to docker hub, and I tried to deploy my container with both ways

kompose up

and

kompose convert -f docker-compose.yaml kubectl create -f (deplymentfiles)

But I get this response

WARN Volume mount on the host "/home/App/src/main/docker/postgres-data" isn't supported - ignoring path on the host 
INFO We are going to create Kubernetes Deployments, Services and PersistentVolumeClaims for your Dockerized application. If you need different kind of resources, use the 'kompose convert' and 'kubectl create -f' commands instead. 

INFO Deploying application in "default" namespace 
INFO Successfully created Service: adminer        
INFO Successfully created Service: app            
INFO Successfully created Service: mypostgres     
INFO Successfully created Deployment: adminer     
INFO Successfully created Deployment: app         
INFO Successfully created Deployment: mypostgres  
INFO Successfully created PersistentVolumeClaim: mypostgres-claim0 of size 100Mi. If your cluster has dynamic storage provisioning, you don't have to do anything. Otherwise you have to create PersistentVolume to make PVC work 

when I run kubectl get pods

NAME                           READY     STATUS             RESTARTS   AGE
adminer-6cd96f8846-69qb8       1/1       Running            0          2m
app-5796c489ff-m46xk           0/1       ImagePullBackOff   0          2m
mypostgres-649865b4d8-nhglj    1/1       Running            0          2m

kubectl describe pod app-5796c489ff-m46xk

shows this

Name:           app-5796c489ff-m46xk
Namespace:      default
Node:           minikube/192.168.99.100
Start Time:     Mon, 11 Jun 2018 11:02:32 +0200
Labels:         io.kompose.service=app
                pod-template-hash=1352704599
Annotations:    <none>
Status:         Pending
IP:             172.17.0.3
Controlled By:  ReplicaSet/app-5796c489ff
Containers:
  app:
    Container ID:   
    Image:          iroolapp
    Image ID:       
    Port:           8086/TCP
    Host Port:      0/TCP
    State:          Waiting
      Reason:       ImagePullBackOff
    Ready:          False
    Restart Count:  0
    Environment:
      DATABASE_HOST:      mypostgres
      DATABASE_NAME:      test
      DATABASE_PASSWORD:  root
      DATABASE_PORT:      5432
      DATABASE_USER:      root
    Mounts:
      /var/run/secrets/kubernetes.io/serviceaccount from default-token-wdb8n (ro)
Conditions:
  Type           Status
  Initialized    True 
  Ready          False 
  PodScheduled   True 
Volumes:
  default-token-wdb8n:
    Type:        Secret (a volume populated by a Secret)
    SecretName:  default-token-wdb8n
    Optional:    false
QoS Class:       BestEffort
Node-Selectors:  <none>
Tolerations:     <none>
Events:
  Type     Reason                 Age              From               Message
  ----     ------                 ----             ----               -------
  Normal   Scheduled              3m               default-scheduler  Successfully assigned app-5796c489ff-m46xk to minikube
  Normal   SuccessfulMountVolume  3m               kubelet, minikube  MountVolume.SetUp succeeded for volume "default-token-wdb8n"
  Normal   Pulling                1m (x4 over 3m)  kubelet, minikube  pulling image "iroolapp"
  Warning  Failed                 1m (x4 over 3m)  kubelet, minikube  Failed to pull image "iroolapp": rpc error: code = Unknown desc = Error response from daemon: pull access denied for iroolapp, repository does not exist or may require 'docker login'
  Warning  Failed                 1m (x4 over 3m)  kubelet, minikube  Error: ErrImagePull
  Normal   BackOff                1m (x6 over 3m)  kubelet, minikube  Back-off pulling image "iroolapp"
  Warning  Failed                 1m (x6 over 3m)  kubelet, minikube  Error: ImagePullBackOff

Finally this is my docker-compose file

version: '3'
services:
  app:
    image: iroolapp
    depends_on:
    - mypostgres
    ports:
     - "9000:8086"
    environment:
      - DATABASE_HOST=mypostgres
      - DATABASE_USER=root
      - DATABASE_PASSWORD=root
      - DATABASE_NAME=test
      - DATABASE_PORT=5432

    networks:
        default:

  mypostgres:
    image: postgres:9.6-alpine
    container_name: mypostgres

    ports:
     - "5433:5432"


    environment:
     - POSTGRES_PASSWORD=root
     - POSTGRES_USER=root
     - POSTGRES_DB=irooldb
    volumes:
    - ./postgres-data:/var/lib/postgresql/data

  adminer:
    image: adminer
    ports:
      - 8080:8080
    networks:
        default:

networks:
   default:
      external:
        name: mynetwork

My question is: what does ImagePullBackoff refers to? using kompose is it a good approach? and is it a necessary step to push images to docker hub before using kubernetes