Flask + Docker + Kubernetes Application

📋 Overview#

This repository contains everything needed to deploy a scalable Flask web application with a PostgreSQL database using Docker for containerization and Kubernetes for orchestration, suitable for microservices and cloud‑native applications.​

🏗️ Project Structure#

flask-app/
├── app.py # Main Flask application
├── Dockerfile # Docker configuration for Flask app
└── requirements.txt # Python dependencies

K8s/
├── configmap.yaml # ConfigMap for non-sensitive configuration
├── flask-deployment.yaml # Deployment configuration for Flask app
├── ingress.yaml # Ingress for external access
├── postgres.deployment.yaml# Deployment configuration for Postgres
└── secret.yaml # Secret for sensitive configuration

🔧 Flask Application#

The Flask app connects to PostgreSQL and exposes health and database‑check endpoints for Kubernetes probes, with configuration driven by environment variables.​

Key features:​

• PostgreSQL integration

• Environment‑variable based configuration

• Health check endpoint for probes

• Database connection test endpoint

Requirements#

Flask==2.3.3 psycopg2-binary==2.9.9 gunicorn==21.2.0

🐳 Docker Setup#

Build the image:​

cd flask-app
docker build -t mypyapp:latest .

Create Docker network:​

docker network create my-app-network

Run PostgreSQL:​

docker run -d \
 --name postgres-db \
 --network my-app-network \
 -e POSTGRES_USER=myuser \
 -e POSTGRES_PASSWORD=mypassword \
 -e POSTGRES_DB=mydatabase \
 -p 5432:5432 \
 -v postgres_data:/var/lib/postgresql/data \
 postgres:13

Run Flask container:​

docker run -d \
 --name mypyapp \
 --network my-app-network \
 -e POSTGRES_HOST=postgres-db \
 -e POSTGRES_DB=mydatabase \
 -e POSTGRES_USER=myuser \
 -e POSTGRES_PASSWORD=mypassword \
 -p 5000:5000 \
 mypyapp

☸️ Kubernetes Deployment#

Create namespace:​

kubectl create namespace dev-app

Apply configs in order:​

kubectl apply -f K8s/configmap.yaml
kubectl apply -f K8s/secret.yaml
kubectl apply -f K8s/postgres.deployment.yaml
kubectl apply -f K8s/flask-deployment.yaml
kubectl apply -f K8s/ingress.yaml

Verify:​

kubectl get pods -n dev-app
kubectl get services -n dev-app
kubectl get deployments -n dev-app

🔍 Kubernetes Objects#

• ConfigMap: non‑sensitive config such as DB host and app environment.​

• Secret: DB credentials stored securely.​

• PostgreSQL Deployment: persistent volume, env vars from ConfigMap/Secret, internal headless service.​

• Flask Deployment: multiple replicas, resource limits, liveness/readiness probes, env from ConfigMap/Secret.​

• Ingress: external access with host/path routing via an ingress controller.​

🛠️ Troubleshooting#

# View logs
kubectl logs -n dev-app <pod-name>

# Describe pod
kubectl describe pod -n dev-app <pod-name>

# Port-forward
kubectl port-forward -n dev-app service/flask-service 8080:80

# Exec into pod
kubectl exec -it -n dev-app <pod-name> -- /bin/bash

📊 Scaling#

kubectl scale -n dev-app deployment/flask-app --replicas=5

🔄 CI/CD Integration#

Typical flow:​

1. Build Docker image in CI.

2. Push image to a container registry.

3. Update Kubernetes deployment with new image tag.

4. Apply any updated manifests.

🔒 Security#

• DB credentials in Kubernetes Secrets.​

• Optional network policies for traffic control.

• Resource limits to avoid resource exhaustion.

• Probes to ensure only healthy pods receive traffic.​

📚 References#

• Flask, Docker, Kubernetes, and PostgreSQL official docs are recommended for deeper dives into configuration and best practices.​

1. https://github.com/sagesta/Deploy-Backend-with-Kubernetes