httpd Docker image CrashLoopBackOff on Kubernetes - docker

Question

I have a simple docker image which is working fine locally.
It is basically the same as the example on apache's httpd page.
FROM httpd:2.4
COPY ./public-html/ /usr/local/apache2/htdocs/
As per the page example, I can build and run my image as follows:
$ docker build -t gcr.io/${PROJECT_ID}/hello-app:v1 .
$ docker run -dit --name my-running-app -p 8080:80 <img_id>
I then head over to http://localhost:8080 , and everything seems to be working as it should.
However, when I try to create a deployment for my Google Cloud Kubernetes instance, my pod fails and gets to the state of CrashLoopBackOff. (This is after I have pushed the image to Google Cloud Registry, so that the deployment may grab the image from there.)
I think that this CrashLoopBackOff problem is happening due to me not having an ENTRYPOINT to my container; ie, the pod spawns, no command is issued, and then it is completed and crashes.
I have 2 questions then:
What command should I add to my Dockerfile to get the http server up and running on the pod (assuming my assessment of the problem is indeed correct)?
How is this running locally? Locally I simply $ docker run -dit --name my-running-app -p 8080:80 <img_id>. I do not specify that the container should run httpd, yet it does? How is this happening?
Edit - additional information:
I deployed onto K8's by doing the following:
$ kubectl create deployment hello-app --image=gcr.io/${PROJECT_ID}/hello-app:v1
Kubectl logs:
$ kubectl logs <pod_name>
standard_init_linux.go:211: exec user process caused "exec format error"
kubectl describe:
$ kubectl describe pod hello-app-6b89cd98f6-gn65p
Name: <name>
Namespace: default
Priority: 0
Node: <my_node>
Start Time: Mon, 22 Mar 2021 12:32:51 +0200
Labels: app=hello-app
pod-template-hash=6b89cd98f6
Annotations: <none>
Status: Running
IP: 10.12.1.13
IPs:
IP: 10.12.1.13
Controlled By: <replica_set>
Containers:
hello-app:
Container ID: <cid>
Image: <img>
Image ID: <img_id>
Port: <none>
Host Port: <none>
State: Waiting
Reason: CrashLoopBackOff
Last State: Terminated
Reason: Error
Exit Code: 1
Started: Mon, 22 Mar 2021 15:12:18 +0200
Finished: Mon, 22 Mar 2021 15:12:18 +0200
Ready: False
Restart Count: 36
Environment: <none>
Mounts:
/var/run/secrets/kubernetes.io/serviceaccount from default-token-b8p9t (ro)
Conditions:
Type Status
Initialized True
Ready False
ContainersReady False
PodScheduled True
Volumes:
default-token-b8p9t:
Type: Secret (a volume populated by a Secret)
SecretName: default-token-b8p9t
Optional: false
QoS Class: BestEffort
Node-Selectors: <none>
Tolerations: node.kubernetes.io/not-ready:NoExecute op=Exists for 300s
node.kubernetes.io/unreachable:NoExecute op=Exists for 300s
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Warning BackOff 4m9s (x741 over 164m) kubelet Back-off restarting failed container

Answer 1

CrashLoopBackOff error means the pod keeps crashing and kubernetes has given up on it. You have to determine what is causing the crash.
Overally the cause of problem may be that:
type of parameters of the pod or container have been configured incorrectly
the application inside the container keeps crashing
an error occurred while deploying Kubernetes
You can type watch kubectl describe <pod-name> to check events as the pod is being created. But if the pod crashes after it starts up, you need to get the container logs kubectl logs -f <your-pod-name>.
Read more: kubernetes-crashloopbackoff.
As #Krishna Chaurasia said check the thread which is implying that the default command being run is not an executable - executable formats could be different for different platforms. As #Sagar Velankar mentioned use in Docker file in FROM line --platform flag to specify linux/amd64 as the target architecture. See: dockerfile-from.
You can use docker buildx docs.docker.com/docker-for-mac/multi-arch to build and push multi architecture images and kubelet will pull the image with correct architecture.