Docker containerization in FastAPI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the base image for a FastAPI Docker container.

FastAPI

FROM [1]

Drag options to blanks, or click blank then click option'

Aalpine:latest

Bnode:latest

Cubuntu:20.04

Dpython:3.12-slim

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a Node.js or Ubuntu base image which is not optimized for Python FastAPI.

The base image python:3.12-slim is suitable for FastAPI apps using Python 3.12.

2fill in blank

medium

Complete the code to copy the application files into the Docker image.

FastAPI

COPY [1] /app

Drag options to blanks, or click blank then click option'

ADockerfile

Brequirements.txt

C.

Dmain.py

Attempts:

3 left

💡 Hint

Common Mistakes

Copying only one file like main.py or requirements.txt, missing other files.

Copying . copies all files from the current directory into the image's /app folder.

3fill in blank

hard

Fix the error in the command to install dependencies inside the Dockerfile.

FastAPI

RUN pip install [1] -r requirements.txt

Drag options to blanks, or click blank then click option'

A--requirement

B--install

C--upgrade

D--require

Attempts:

3 left

💡 Hint

Common Mistakes

Using invalid flags like --install or --require which cause errors.

The correct flag to specify a requirements file is -r or --requirement. The --upgrade flag upgrades packages but does not specify the requirements file.

4fill in blank

hard

Fill both blanks to expose the correct port and run the FastAPI app with uvicorn.

FastAPI

EXPOSE [1]
CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "[2]"]

Drag options to blanks, or click blank then click option'

A8000

B8080

C5000

D80

Attempts:

3 left

💡 Hint

Common Mistakes

Using different ports for expose and run causing connection issues.

FastAPI by default runs on port 8000. Exposing and running on the same port ensures accessibility.

5fill in blank

hard

Fill all three blanks to create a Dockerfile snippet that sets the working directory, copies files, and installs dependencies.

FastAPI

WORKDIR [1]
COPY [2] .
RUN pip install -r [3]

Drag options to blanks, or click blank then click option'

A/app

B.

Crequirements.txt

D/src

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong working directory or copying wrong files or missing requirements.txt.

Setting /app as working directory, copying current directory files, and installing from requirements.txt is standard practice.

Practice

1. What is the main purpose of using Docker with a FastAPI application?

easy

A. To package the app and its environment so it runs the same everywhere

B. To write the FastAPI code faster

C. To replace the need for Python in the app

D. To automatically generate API documentation

Solution

1. Step 1: Understand Docker's role

   Docker packages an app with all its dependencies into a container.

2. Step 2: Recognize the benefit for FastAPI

   This container runs the app the same way on any machine, avoiding environment issues.

3. Final Answer:

   To package the app and its environment so it runs the same everywhere -> Option A

4. Quick Check:

   Docker ensures consistent app environment = A [OK]

Hint: Docker ensures your app runs identically on any machine [OK]

Common Mistakes:

• Thinking Docker speeds up coding
• Believing Docker replaces Python
• Confusing Docker with API doc tools

2. Which line correctly sets the base image in a Dockerfile for a FastAPI app using Python 3.12?

easy

A. BASE python:3.12

B. FROM python:3.12-slim

C. IMAGE python:latest

D. START python:3.12

Solution

1. Step 1: Recall Dockerfile syntax for base image

   The correct keyword to set the base image is FROM followed by the image name.

2. Step 2: Match the correct Python version format

   python:3.12-slim is a valid lightweight Python 3.12 image.

3. Final Answer:

   FROM python:3.12-slim -> Option B

4. Quick Check:

   Base image line starts with FROM = A [OK]

Hint: Dockerfile base image always starts with FROM keyword [OK]

Common Mistakes:

• Using BASE or IMAGE instead of FROM
• Omitting the version tag
• Using START which is invalid

3. Given this Dockerfile snippet for FastAPI, what will happen when you run the container?

FROM python:3.12-slim
WORKDIR /app
COPY . /app
RUN pip install fastapi uvicorn
CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"]

medium

A. The container will fail because pip install is missing requirements.txt

B. The app will start but only listen on localhost inside the container

C. The FastAPI app will start and listen on port 8000 inside the container

D. The container will build but not run the app automatically

Solution

1. Step 1: Analyze the CMD command

   The CMD runs uvicorn with host 0.0.0.0 and port 8000, which means it listens on all interfaces inside the container.

2. Step 2: Check the RUN command

   pip installs fastapi and uvicorn directly, so dependencies are present for the app to run.

3. Final Answer:

   The FastAPI app will start and listen on port 8000 inside the container -> Option C

4. Quick Check:

   CMD runs uvicorn on 0.0.0.0:8000 = B [OK]

Hint: uvicorn host 0.0.0.0 means listen on all container interfaces [OK]

Common Mistakes:

• Assuming pip install needs requirements.txt always
• Thinking 0.0.0.0 means localhost only
• Believing CMD does not run automatically

4. You wrote this Dockerfile but your FastAPI app does not start inside the container:

FROM python:3.12-slim
WORKDIR /app
COPY . /app
RUN pip install -r requirements.txt
CMD uvicorn main:app --host 0.0.0.0 --port 8000

What is the likely error?

medium

A. CMD should be a JSON array, not a plain string

B. WORKDIR should be set after COPY

C. pip install command is missing fastapi package

D. COPY command should use absolute paths

Solution

1. Step 1: Check CMD syntax

   CMD should be given as a JSON array to avoid shell parsing issues in Dockerfiles.

2. Step 2: Identify the correct CMD format

   Correct CMD is: ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000"]

3. Final Answer:

   CMD should be a JSON array, not a plain string -> Option A

4. Quick Check:

   CMD must be JSON array for correct execution = C [OK]

Hint: Use JSON array for CMD to run commands properly in Docker [OK]

Common Mistakes:

• Writing CMD as a plain string instead of array
• Changing WORKDIR order unnecessarily
• Assuming pip install misses fastapi if requirements.txt exists

5. You want to optimize your FastAPI Docker image to be smaller and faster to build. Which approach is best?

hard

A. Use the latest Python image without specifying a version

B. Install all packages globally on your host machine before building

C. Copy the entire project including unnecessary files into the image

D. Use a multi-stage Dockerfile with a build stage and a slim final stage

Solution

1. Step 1: Understand multi-stage builds

   Multi-stage builds allow building dependencies in one stage and copying only needed files to a smaller final image.

2. Step 2: Recognize benefits for FastAPI Docker images

   This reduces image size and speeds up build by excluding build tools and caches from the final image.

3. Final Answer:

   Use a multi-stage Dockerfile with a build stage and a slim final stage -> Option D

4. Quick Check:

   Multi-stage builds optimize image size and build speed = D [OK]

Hint: Multi-stage Dockerfiles keep images small and fast to build [OK]

Common Mistakes:

• Installing packages on host instead of inside container
• Copying unnecessary files bloats image
• Using latest tag risks unexpected changes