What is the meaning of ImagePullBackOff status on

Question

I'm trying to run my first kubernetes pod locally. I've run the following command (from here):

export ARCH=amd64
docker run -d \
    --volume=/:/rootfs:ro \
    --volume=/sys:/sys:ro \
    --volume=/var/lib/docker/:/var/lib/docker:rw \
    --volume=/var/lib/kubelet/:/var/lib/kubelet:rw \
    --volume=/var/run:/var/run:rw \
    --net=host \
    --pid=host \
    --privileged \
    gcr.io/google_containers/hyperkube-${ARCH}:${K8S_VERSION} \
    /hyperkube kubelet \
        --containerized \
        --hostname-override=127.0.0.1 \
        --api-servers=http://localhost:8080 \
        --config=/etc/kubernetes/manifests \
        --cluster-dns=10.0.0.10 \
        --cluster-domain=cluster.local \
        --allow-privileged --v=2

Then, I've trying to run the following:

kubectl create -f ./run-aii.yaml

run-aii.yaml:

apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  name: aii
spec:
  replicas: 2
  template:
    metadata:
      labels:
        run: aii
    spec:
      containers:
      - name: aii
        image: aii
        ports:
        - containerPort: 5144
        env:
        - name: KAFKA_IP
          value: kafka
        volumeMounts:
        - mountPath: /root/script
          name: scripts-data
          readOnly: true
        - mountPath: /home/aii/core
          name: core-aii
          readOnly: true
        - mountPath: /home/aii/genome
          name: genome-aii
          readOnly: true
        - mountPath: /home/aii/main
          name: main-aii
          readOnly: true
      - name: kafka
        image: kafkazoo
        volumeMounts:
        - mountPath: /root/script
          name: scripts-data
          readOnly: true
        - mountPath: /root/config
          name: config-data
          readOnly: true
      - name: ws
        image: ws
        ports:
        - containerPort: 3000
      volumes:
      - name: scripts-data
        hostPath:
          path: /home/aii/general/infra/script
      - name: config-data
        hostPath:
          path: /home/aii/general/infra/config
      - name: core-aii
        hostPath: 
          path: /home/aii/general/core
      - name: genome-aii
        hostPath: 
          path: /home/aii/general/genome
      - name: main-aii
        hostPath: 
          path: /home/aii/general/main

Now, when I run: kubectl get pods I'm getting:

NAME                    READY     STATUS             RESTARTS   AGE
aii-806125049-18ocr     0/3       ImagePullBackOff   0          52m
aii-806125049-6oi8o     0/3       ImagePullBackOff   0          52m
aii-pod                 0/3       ImagePullBackOff   0          23h
k8s-etcd-127.0.0.1      1/1       Running            0          2d
k8s-master-127.0.0.1    4/4       Running            0          2d
k8s-proxy-127.0.0.1     1/1       Running            0          2d
nginx-198147104-9kajo   1/1       Running            0          2d

BTW: docker images return:

REPOSITORY                                 TAG                 IMAGE ID            CREATED             SIZE
ws                                         latest              fa7c5f6ef83a        7 days ago          706.8 MB
kafkazoo                                   latest              84c687b0bd74        9 days ago          697.7 MB
aii                                        latest              bd12c4acbbaf        9 days ago          1.421 GB
node                                       4.4                 1a93433cee73        11 days ago         647 MB
gcr.io/google_containers/hyperkube-amd64   v1.2.4              3c4f38def75b        11 days ago         316.7 MB
nginx                                      latest              3edcc5de5a79        2 weeks ago         182.7 MB
docker_kafka                               latest              e1d954a6a827        5 weeks ago         697.7 MB
spotify/kafka                              latest              30d3cef1fe8e        12 weeks ago        421.6 MB
wurstmeister/zookeeper                     latest              dc00f1198a44        3 months ago        468.7 MB
centos                                     latest              61b442687d68        4 months ago        196.6 MB
centos                                     centos7.2.1511      38ea04e19303        5 months ago        194.6 MB
gcr.io/google_containers/etcd              2.2.1               a6cd91debed1        6 months ago        28.19 MB
gcr.io/google_containers/pause             2.0                 2b58359142b0        7 months ago        350.2 kB
sequenceiq/hadoop-docker                   latest              5c3cc170c6bc        10 months ago       1.766 GB

why do I get the ImagePullBackOff ??

Answer 1

The issue arises when the image is not present on the cluster and k8s engine is going to pull the respective registry. k8s Engine enables 3 types of ImagePullPolicy mentioned :

1. Always : It always pull the image in container irrespective of changes in the image
2. Never : It will never pull the new image on the container
3. IfNotPresent : It will pull the new image in cluster if the image is not present.

Best Practices : It is always recommended to tag the new image in both docker file as well as k8s deployment file. So That it can pull the new image in container.

Answer 2

I had this error when I tried to create a replicationcontroller. The issue was, I wrongly spelt the nginx image name in template definition.

Note: This error occurs when kubernetes is unable to pull the specified image from the repository.