We are going to build a docker image locally and then run a Pod inside the Kubernetes cluster with that image.
Build a docker image locally using dockerfile.
Save the following docker file ubuntu-sleep.dockerfile
FROM ubuntu
ENTRYPOINT ["sleep"]
CMD ["5"]
Build image docker build -t ubuntu-sleep -f ubuntu-sleep.dockerfile .
(base) ~/code/devops/kubernetes/CKAD (master ✗) docker build -t ubuntu-sleep -f ubuntu-sleep.dockerfile .
[+] Building 0.1s (5/5) FINISHED
=> [internal] load build definition from ubuntu-sleeper.dockerfile 0.0s
=> => transferring dockerfile: 51B 0.0s
=> [internal] load .dockerignore 0.0s
=> => transferring context: 2B 0.0s
=> [internal] load metadata for docker.io/library/ubuntu:latest 0.0s
=> CACHED [1/1] FROM docker.io/library/ubuntu 0.0s
=> exporting to image 0.0s
=> => exporting layers 0.0s
=> => writing image sha256:b739783c0472bbc0008474a0e9f1c5a55dc0419fd4d7851bed8b08fec7596332 0.0s
=> => naming to docker.io/library/ubuntu-sleep
Create a Kind Cluster with the name demo.
kind create cluster --name=demo
(base) ~/code/devops/kubernetes/CKAD (master ✗) kind create cluster --name=demo
Creating cluster "demo" ...
✓ Ensuring node image (kindest/node:v1.25.3) 🖼
✓ Preparing nodes 📦
✓ Writing configuration 📜
✓ Starting control-plane 🕹️
✓ Installing CNI 🔌
✓ Installing StorageClass 💾
Set kubectl context to "kind-demo"
You can now use your cluster with:
kubectl cluster-info --context kind-demo
Have a nice day! 👋
Load the docker image to the kind cluster demo
kind load docker-image ubuntu-sleep --name demo
(base) ~/code/devops/kubernetes/CKAD (master ✗) kind load docker-image ubuntu-sleep --name demo
Image: "" with ID "sha256:b739783c0472bbc0008474a0e9f1c5a55dc0419fd4d7851bed8b08fec7596332" not yet present on node "demo-control-plane", loading...
Kind load is a very useful command and provides multiple options as well. To get more info about the kind load command use the -h option.
Run a pod inside the demo cluster with the following command
kubectl run ubuntu-sleep --image=ubuntu-sleep
(base) ~/code/devops/kubernetes/CKAD (master ✗) kubectl run ubuntu-sleep --image=ubuntu-sleep
pod/ubuntu-sleep created
(base) ~/code/devops/kubernetes/CKAD (master ✗) kubectl get pod ubuntu-sleep
NAME READY STATUS RESTARTS AGE
ubuntu-sleep 0/1 ImagePullBackOff 0 14s
When we check the pod status it is ImagePullBackOff which means it is failing in running the container with the given image. Wait, what did we do wrong?
Lets, try to debug the problem. As we all know the Kind runs a kubernetes cluster inside docker right? KIND (Kubernetes Inside Docker)
Run the following command to check if the image is already available.
(base) ~/code/devops/kubernetes/CKAD (master ✗) docker exec -it demo-control-plane crictl images
IMAGE TAG IMAGE ID SIZE
docker.io/kindest/kindnetd v20221004-44d545d1 7ba9b35cf55e6 23.7MB
docker.io/kindest/local-path-helper v20220607-9a4d8d2a 304f67e47fc80 2.75MB
docker.io/kindest/local-path-provisioner v0.0.22-kind.0 7902f9a1c54fa 15.6MB
docker.io/library/ubuntu-sleep latest b739783c0472b 71.8MB
registry.k8s.io/coredns/coredns v1.9.3 b19406328e70d 13.4MB
registry.k8s.io/etcd 3.5.4-0 8e041a3b0ba8b 81.1MB
registry.k8s.io/kube-apiserver v1.25.3 feafd6a91eb52 74.2MB
registry.k8s.io/kube-controller-manager v1.25.3 05b17bba8656e 62.3MB
registry.k8s.io/kube-proxy v1.25.3 aa31a9b19ccdf 59.6MB
registry.k8s.io/kube-scheduler v1.25.3 253d0aeea8c69 50.6MB
registry.k8s.io/pause 3.7 e5a475a038057 268kB
Yeah! it's there. Then what the hack problem is?
If we sit back and relax and look again at the pod events we see it is trying to pull the image, but why? we already have that in our local system.
ahhh! we didn't specify the pull policy and the default one is imagePullPolicy: Always
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled 12m default-scheduler Successfully assigned default/ubuntu-sleep to demo-control-plane
Normal Pulling 10m (x4 over 12m) kubelet Pulling image "ubuntu-sleep"
Warning Failed 10m (x4 over 12m) kubelet Failed to pull image "ubuntu-sleep": rpc error: code = Unknown desc = failed to pull and unpack image "docker.io/library/ubuntu-sleep:latest": failed to resolve reference "docker.io/library/ubuntu-sleep:latest": pull access denied, repository does not exist or may require authorization: server message: insufficient_scope: authorization failed
Warning Failed 10m (x4 over 12m) kubelet Error: ErrImagePull
Warning Failed 10m (x6 over 12m) kubelet Error: ImagePullBackOff
Normal BackOff 2m19s (x43 over 12m) kubelet Back-off pulling image "ubuntu-sleep"
Run the pod again, this time with image-pull-policy option
kubectl run ubuntu-sleep-1 --image=ubuntu-sleep --image-pull-policy=Never
(base) ~/code/devops/kubernetes/CKAD (master ✗) kubectl run ubuntu-sleep-1 --image=ubuntu-sleep --image-pull-policy=Never
pod/ubuntu-sleep-1 created
(base) ~/code/devops/kubernetes/CKAD (master ✗) kubectl get pod
NAME READY STATUS RESTARTS AGE
ubuntu-sleep 0/1 ImagePullBackOff 0 8m16s
ubuntu-sleep-1 1/1 Running 0 5s
(base) ~/code/devops/kubernetes/CKAD (master ✗)
woala!!! It is working and the container is running!
Happy Learning...
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