Docker containerization in Flask - Step-by-Step Execution

Concept Flow - Docker containerization

Write Flask app code

↓

Create Dockerfile

↓

Build Docker image

↓

Run Docker container

↓

App runs inside container

↓

Access app via browser or curl

This flow shows how you write a Flask app, create a Dockerfile, build an image, run a container, and access the app.

Execution Sample

Flask

FROM python:3.12-slim
WORKDIR /app
COPY requirements.txt ./
RUN pip install -r requirements.txt
COPY . ./
CMD ["python", "app.py"]

This Dockerfile sets up a Python 3.12 environment, installs dependencies, copies app files, and runs the Flask app.

Execution Table

Step	Action	Details	Result
1	Write Flask app	Create app.py with Flask code	Flask app code ready
2	Create Dockerfile	Define base image and commands	Dockerfile ready
3	Build image	Run 'docker build -t flask-app .'	Docker image 'flask-app' created
4	Run container	Run 'docker run -p 5000:5000 flask-app'	Container runs Flask app on port 5000
5	Access app	Open http://localhost:5000 in browser	Flask app page loads
6	Stop container	Ctrl+C or 'docker stop <container_id>'	Container stops
7	Exit	No more commands	Process ends

💡 Process ends after container stops and no further commands run

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	Final
Flask app code	None	app.py created	app.py present	app.py in image	app.py running in container	app.py serving requests	app.py stopped
Dockerfile	None	None	Dockerfile created	Dockerfile used in image	Dockerfile not needed now	Dockerfile not needed	Dockerfile not needed
Docker image	None	None	None	Image 'flask-app' built	Image running as container	Image running	Image remains
Docker container	None	None	None	None	Container running	Container running	Container stopped

Key Moments - 3 Insights

Why do we need a Dockerfile after writing the Flask app?

The Dockerfile tells Docker how to build the image with the app and its environment. Without it, Docker doesn't know what to include or how to run the app. See execution_table step 2.

What happens when we run 'docker build'?

Docker reads the Dockerfile and creates an image with all files and dependencies. This image is like a snapshot of the app environment. See execution_table step 3.

Why do we map ports when running the container?

Mapping ports (like 5000:5000) connects the container's internal port to the host machine, so you can access the Flask app from your browser. See execution_table step 4.

Visual Quiz - 3 Questions

Look at the execution table, what is the result after step 3?

A Docker container stopped

B Flask app code running

C Docker image 'flask-app' created

D Dockerfile deleted

💡 Hint

Check the 'Result' column for step 3 in the execution_table

At which step does the Flask app start running inside the container?

A Step 4

B Step 3

C Step 2

D Step 5

💡 Hint

Look for when the container runs the Flask app in the execution_table

If you forget to map ports when running the container, what changes in the execution?

A The container will not start

B You cannot access the app from the browser

C The Docker image will not build

D The Flask app code will be missing

💡 Hint

Think about the port mapping explained in key_moments and execution_table step 4

Concept Snapshot

Docker containerization with Flask:
1. Write Flask app code (app.py).
2. Create Dockerfile to define environment.
3. Build Docker image with 'docker build'.
4. Run container with port mapping 'docker run -p'.
5. Access app via localhost port.
6. Container isolates app and dependencies.

Full Transcript

Docker containerization for a Flask app involves writing the app code, creating a Dockerfile to specify the environment, building a Docker image from that Dockerfile, and running a container from the image. The container runs the Flask app isolated from the host system. Port mapping allows access to the app from a browser. The process stops when the container is stopped.