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Kubernetes Hello World

A Kubernetes Hello World Project for Python Flask. This project uses a simple Flask app that returns correct change as the base project and converts it to Kubernetes.

This recipe is in the book Practical MLOps.

Assets in Repo

• Makefile: Builds project
• Dockerfile: Container configuration
• app.py: Flask app
• kube-hello-change.yaml: Kubernetes YAML Config

Get Started

• Create Python virtual environment python3 -m venv ~/.kube-hello && source ~/.kube-hello/bin/activate
• Run make all to install python libraries, lint project, including Dockerfile and run tests

Build and Run Docker Container

• Install Docker Desktop

• To build the image locally do the following.

docker build -t flask-change:latest . or run make build which has the same command.

• To verify container run docker image ls

• To run do the following: docker run -p 8080:8080 flask-change or run make run which has the same command

• In a separate terminal invoke the web service via curl, or run make invoke which has the same command

curl http://127.0.0.1:8080/change/1/34

[
  {
    "5": "quarters"
  }, 
  {
    "1": "nickels"
  }, 
  {
    "4": "pennies"
  }
]

• Stop the running docker container by using control-c command

Running Kubernetes Locally

• Verify Kubernetes is working via docker-desktop context

(.kube-hello) ➜  kubernetes-hello-world-python-flask git:(main) kubectl get nodes
NAME             STATUS   ROLES    AGE   VERSION
docker-desktop   Ready    master   30d   v1.19.3

• Run the application in Kubernetes using the following command which tells Kubernetes to setup the load balanced service and run it:

kubectl apply -f kube-hello-change.yaml or run make run-kube which has the same command

You can see from the config file that a load-balancer along with three nodes is the configured application.

apiVersion: v1
kind: Service
metadata:
  name: hello-flask-change-service
spec:
  selector:
    app: hello-python
  ports:
  - protocol: "TCP"
    port: 8080
    targetPort: 8080
  type: LoadBalancer

---
apiVersion: apps/v1
kind: Deployment
metadata:
  name: hello-python
spec:
  selector:
    matchLabels:
      app: hello-python
  replicas: 3
  template:
    metadata:
      labels:
        app: hello-python
    spec:
      containers:
      - name: flask-change
        image: flask-change:latest
        imagePullPolicy: Never
        ports:
        - containerPort: 8080

• Verify the container is running

kubectl get pods

Here is the output:

NAME                            READY   STATUS    RESTARTS   AGE
flask-change-7b7d7f467b-26htf   1/1     Running   0          8s
flask-change-7b7d7f467b-fh6df   1/1     Running   0          7s
flask-change-7b7d7f467b-fpsxr   1/1     Running   0          6s

• Describe the load balanced service:

kubectl describe services hello-python-service

You should see output similar to this:

Name:                     hello-python-service
Namespace:                default
Labels:                   <none>
Annotations:              <none>
Selector:                 app=hello-python
Type:                     LoadBalancer
IP Families:              <none>
IP:                       10.101.140.123
IPs:                      <none>
LoadBalancer Ingress:     localhost
Port:                     <unset>  8080/TCP
TargetPort:               8080/TCP
NodePort:                 <unset>  30301/TCP
Endpoints:                10.1.0.27:8080,10.1.0.28:8080,10.1.0.29:8080
Session Affinity:         None
External Traffic Policy:  Cluster
Events:                   <none>

Invoke the endpoint to curl it:

make invoke

curl http://127.0.0.1:8080/change/1/34
[
  {
    "5": "quarters"
  }, 
  {
    "1": "nickels"
  }, 
  {
    "4": "pennies"
  }
]

To cleanup the deployment do the following: kubectl delete deployment hello-python

References

• Azure Kubernetes deployment strategy
• Service Cluster Config YAML file
• Kubernetes.io Hello World