Awesome

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. kubernetes-load-balanced-cluster

This recipe is in the book Practical MLOps.

9781098103002

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"
  }
]