How to deploy containerized Flask application to a Kubernetes with Kubeadm on Virtual Machines - Part 3
May 21, 2023
This is the third and final part of a series of hands-on tutorials for deploying containerized Flask application to a Kubernetes with Kubeadm on Virtual Machines.
Series
Overview
In this tutorial, we are going to
- Install Docker
- Write Flask application
- Contanerize Flask application
- Push Docker image to Docker Hub
- Deploying the container on the cluster
Requirements
- A Docker account. You can sign up here.
1. Docker installation (Master only)
First, we need to install Docker
1.1 Update the apt package index
sudo apt update
sudo apt-get install ca-certificates curl gnupg lsb-release
1.2 Add Docker’s official GPG key:
sudo mkdir -m 0755 -p /etc/apt/keyrings
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg
1.3 setup repository
echo \
"deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu \
$(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
1.4 Install Docker Engine
sudo apt-get update
sudo apt-get install docker-ce
Select N when asking about Configuration file '/etc/containerd/config.toml' since we already setup in containerd runtime setup section in Part 2.
1.5 (Optional) Executing the Docker Command Without sudo
sudo usermod -aG docker ${USER}
su - ${USER}
2. Write a Flask application (Master only)
2.1 Create a new directory
Create a new directory named helloworld and change the directory into it
mkdir helloworld
cd helloworld
2.2 Write Flask API
Create a file named app.py and paste the following code into it.
from flask import Flask
app = Flask(__name__)
@app.route("/")
def hello_world():
return "Hello Kubernetes"
if __name__ == "__main__":
app.run(debug=True, host="0.0.0.0", port=8080)
2.3 Add Flask dependency
Create a file named requirements.txt and paste the following code into it.
Flask
3 Contanerize Flask Application (Master only)
3.1 Create a Docker file
Create a file named Dockerfile with the following contents.
# Use the official lightweight Python image.
FROM python:3.10-slim
# Copy local code to the container image.
ENV APP_HOME /app
WORKDIR /app
COPY . ./
# Install production dependencies.
RUN pip install --no-cache-dir -r requirements.txt
# Run the web service on container startup.
CMD [ "flask", "run","--host","0.0.0.0","--port","8080"]
3.2 Build Docker image
Build a Docker image called flask-backend. Since we need to upload to the Docker hub, we need to use our login ID as a preface. So that will become <YOUR-DOCKER-ID>/flask-backed. For my case, I need to use aknay/flask-backend.
docker build --tag aknay/flask-backend .
You can list the docker that you just built by running docker image ls and you should see the following image listed.
REPOSITORY TAG IMAGE ID CREATED SIZE
aknay/flask-backend latest ebc930c236c8 21 minutes ago 136MB
You can remove the docker image using
docker rmi -f <IMAGE ID>
3.3 Testing Docker image locally
You can run the image by running
docker run --detach --publish 8080:8080 <IMAGE ID>
The command is
docker run --detach --publish <TRAFFIC-FROM-PORT>:<TO-CONTAINER-PORT> <IMAGE-ID>
When you run docker ps, you should see an output similar to this.
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
513453b7a0ad aknay/flask-backend "flask run --host 0.…" 18 seconds ago Up 16 seconds 0.0.0.0:8080->8080/tcp, :::8080->8080/tcp naughty_neumann8080/tcp, :::8080->8080/tcp pedantic_almeida
If you use curl localhost:8080 on the terminal, You should see the message Hello Kubernetes on the terminal (which is a reply from our Flask API).
3.4 Stop Docker image
We can now stop the running container with this command docker stop <CONTAINER ID> since we successfully tested the docker.
4. Push the Docker image to Docker Hub (Master only)
We need to push our Docker image to Docker Hub because the image will be later downloaded and deployed on the cluster.
4.1 Login to Docker Hub
Log in to Docker Hub using your username and password
docker login
4.2 Push image to Docker Hub
docker push <YOUR-DOCKER-HUB-ID>/flask-backend
5. Deploying the container on the cluster (Master only)
5.1 Create a deployment
A Deployment provides declarative updates for Pods and ReplicaSets. You can learn more about it from here. So we need a create a deployment.yml first. Note that you need to change the image name (in deployment.yml) based on your docker hub id. Mine is aknay/flask-backend.
kind: Service
apiVersion: v1
metadata:
name: flask-app-service
labels:
app: flask-app
spec:
selector:
app: flask-app
ports:
- port: 8080
targetPort: 8080
type: ClusterIP
---
apiVersion: apps/v1
kind: Deployment
metadata:
name: flask-app
labels:
app: flask-app
spec:
replicas: 2
selector:
matchLabels:
app: flask-app
template:
metadata:
labels:
app: flask-app
spec:
containers:
- name: flask-app
image: aknay/flask-backend
imagePullPolicy: Always
ports:
- containerPort: 8080
protocol: TCP
5.2 Deploying on cluster
Then create the deployment by kubectl apply -f deployment.yml.
Let’s check the service first by kubectl get service. Now our flask-app-service is running.
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
flask-app-service ClusterIP 10.96.101.16 <none> 8080/TCP 12s
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 160m
5.3 Checking deployment
Now we check the deployment by kubectl get deployment. As you see below, our app is running with two replicas (based on what we defined in deployments.yml).
NAME READY UP-TO-DATE AVAILABLE AGE
flask-app 2/2 2 2 107s
5.4 Testing our cluster
Let’s test our app by curl <CLUSTER-IP>:8080 (which is running flash-app-service) and you should see the expected message Hello Kubernetes.
For me, I need to use my cluster IP address
curl 10.96.101.16:8080
Now we successfully deploy our docker image to our cluster.
5.5 (Reference) Listing Pods with Nodes
You can list all pods on nodes using the following command
kubectl get pods --all-namespaces -o wide
You should see the following.
NAMESPACE NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
default flask-app-6bdfd677c5-7gc98 1/1 Running 0 7m48s 10.244.1.4 worker-vbox <none> <none>
default flask-app-6bdfd677c5-t4fjx 1/1 Running 0 7m48s 10.244.1.3 worker-vbox <none> <none>
kube-flannel kube-flannel-ds-c4wfg 1/1 Running 0 147m 10.0.2.15 master-vbox <none> <none>
kube-flannel kube-flannel-ds-p775s 1/1 Running 0 147m 10.0.2.5 worker-vbox <none> <none>
kube-system coredns-5d78c9869d-f5dgw 1/1 Running 0 167m 10.244.1.2 worker-vbox <none> <none>
kube-system coredns-5d78c9869d-f6wmn 1/1 Running 0 167m 10.244.0.2 master-vbox <none> <none>
kube-system etcd-master-vbox 1/1 Running 0 167m 10.0.2.15 master-vbox <none> <none>
kube-system kube-apiserver-master-vbox 1/1 Running 0 167m 10.0.2.15 master-vbox <none> <none>
kube-system kube-controller-manager-master-vbox 1/1 Running 0 167m 10.0.2.15 master-vbox <none> <none>
kube-system kube-proxy-gzcgl 1/1 Running 0 167m 10.0.2.15 master-vbox <none> <none>
kube-system kube-proxy-v5lzg 1/1 Running 0 154m 10.0.2.5 worker-vbox <none> <none>
kube-system kube-scheduler-master-vbox 1/1 Running 0 167m 10.0.2.15 master-vbox <none> <none>
You can see that our two pods in running on the worker as expected.
5.6 (Reference) Cleaning up
- You can delete the deployment with
kubectl kubectl delete -f deployment.ymlor you can deleted individually like so.kubectl delete deployment <YOUR DEPLOYMENT NAME>. - For the service,
kubectl delete service <YOUR SERVICE NAME>
Reference
- https://docs.docker.com/engine/install/ubuntu/
- https://cloud.google.com/run/docs/quickstarts/build-and-deploy/deploy-python-service