Running a two-tier application on Docker is a great way to ensure isolation, scalability, and portability for your apps. In this guide, we’ll deploy a Flask app connected to a MySQL database, using Docker containers on an EC2 instance. By the end, you’ll be able to access your Flask app via your public IP.

Prerequisites

Before we begin, ensure:

Docker is installed on your EC2 instance.
Port 5000 is open in your EC2 security group to access the Flask app.

Step 1: Write a Dockerfile for the Flask Application

The first step is to create a Dockerfile that sets up the Flask app, including all dependencies.

Dockerfile

# Use an official Python runtime as the base image
FROM python:3.9-slim

# Set the working directory in the container
WORKDIR /app

# Install required system packages
RUN apt-get update \
    && apt-get upgrade -y \
    && apt-get install -y gcc default-libmysqlclient-dev pkg-config \
    && rm -rf /var/lib/apt/lists/*

# Copy the requirements file into the container
COPY requirements.txt .

# Install app dependencies
RUN pip install mysqlclient
RUN pip install --no-cache-dir -r requirements.txt

# Copy the rest of the application code
COPY . .

# Expose port 5000 for Flask
#EXPOSE 5000

# Specify the command to run your application
CMD ["python", "app.py"]

This Dockerfile installs necessary dependencies, such as mysqlclient, and sets up the Flask app.

Step 2: Build the Docker Image for the Flask App

With the Dockerfile ready, build the Docker image for the Flask application:

docker build -t flask-app .

This command tags the image as flask-app, which you can verify by running docker images.

Step 3: Create a Docker Network and Volume

To allow communication between the containers, create a custom network. We’ll also create a Docker volume to persist MySQL data.

docker network create flask-mysql-net
docker volume create mysql-data

flask-mysql-net is the network that will connect both containers.
mysql-data is the volume that will store MySQL data, preserving it even if the container stops or is removed.

Step 4: Run the MySQL Container with Network and Volume Attached

Now, start the MySQL container, attaching the flask-mysql-net network and mysql-data volume directly:

docker run --name mysql-container --network flask-mysql-net \
    -v mysql-data:/var/lib/mysql \
    -e MYSQL_ROOT_PASSWORD=admin \
    -e MYSQL_DATABASE=mydb \
    -d mysql:5.7

In this command:

--network flask-mysql-net connects the container to the flask-mysql-net network.
-v mysql-data:/var/lib/mysql mounts the mysql-data volume to MySQL’s data directory (/var/lib/mysql), ensuring data persistence.
-e MYSQL_ROOT_PASSWORD=admin and -e MYSQL_DATABASE=mydb set up the root password and initial database.

Step 5: Run the Flask App Container with Network Attached

Next, run the Flask container and connect it to the flask-mysql-net network, passing the MySQL host as an environment variable.

docker run -p 5000:5000 --name flask-app --network flask-mysql-net \
    -e DATABASE_HOST=mysql-container flask-app

This command:

Maps port 5000 of the container to port 5000 on the EC2 instance, allowing external access.
Connects the Flask container to the flask-mysql-net network.
Sets the DATABASE_HOST environment variable to mysql-container, enabling Flask to communicate with MySQL.

Step 6: Open Port 5000 on EC2 Security Group

To access the Flask app from your browser, open port 5000 in the EC2 security group:

Go to the Security Groups section in your AWS EC2 dashboard.
Edit the Inbound Rules to allow HTTP traffic on port 5000.

With this configuration, you can now access your Flask app via http://your-ec2-public-ip:5000.

Step 7: Verify Data in the MySQL Container

To ensure the connection is successful and data is correctly stored, access the MySQL container and query the database.

Start an interactive session in the MySQL container:
```
 docker exec -it mysql-container bash
```
Enter the MySQL CLI:
```
 mysql -u root -p
```
After entering the password, list the databases and select the flaskdb database to check data:
```
 SHOW DATABASES;
 USE flaskdb;
 SELECT * FROM messages;
```

Access Your Flask App

After setting everything up and opening the necessary port, you can access your application in a web browser using http://your-ec2-public-ip:5000.

Project-05: Deploying a Flask App with MySQL Using Docker on EC2: Attaching Network and Volume