How can I run a cli app in a pod inside a Kubernetes cluster?

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I have a cli app written in NodeJS [not by me].

I want to deploy this on a k8s cluster like I have done many times with web servers.

I have not deployed something like this before, so I am in a kind of a loss.

I have worked with dockerized cli apps [like Terraform] before, and i know how to use them in a CICD.

But how should I deploy them in a pod so they are always available for usage from another app in the cluster?

Or is there a completely different approach that I need to consider?

#EDIT#

I am using this in the end of my Dockerfile ..

# the main executable
ENTRYPOINT ["sleep", "infinity"]
# a default command
CMD ["mycli help"]

That way the pod does not restart and the cli inside is waiting for commands like mycli do this

Is it a hacky way that is frowned upon or a legit solution?

kubernetes command-line-interface
2 Answers

Your edit is one solution, another one if you do not want or cannot change the Docker image is to Define a Command for a Container to loop infinitely, this would achieve the same as the Dockerfile ENTRYPOINT but without having to rebuild the image.

Here's an example of such implementation:

apiVersion: v1
kind: Pod
metadata:
  name: command-demo
  labels:
    purpose: demonstrate-command
spec:
  containers:
  - name: command-demo-container
    image: debian
    command: ["/bin/sh", "-ec", "while :; do echo '.'; sleep 5 ; done"]
  restartPolicy: OnFailure

As for your question about if this is a legit solution, this is hard to answer; I would say it depends on what your application is designed to do. Kubernetes Pods are designed to be ephemeral, so a good solution would be one that is running until the job is completed; for a web server, for example, the job is never completed because it should be constantly listening to requests.

user_169223430

If your pods are in the same cluster they are already available to other pods through Core-DNS. An internal DNS service which allows you to access them by their internal DNS name. Something like my-cli-app.my-namespace.svc.cluster. DNS for service and pods

You would then create a deployment file with all your apps. Note this doesn't need ports to work and also doesn't include communication through the internet.

#deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx-deployment
  labels:
    app: nginx
spec:
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:1.14.2
        ports:
        - containerPort: 80
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