WSGI servers (Gunicorn, uWSGI) in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Flask class from the flask package.

Flask

from flask import [1]
app = Flask(__name__)

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

Ajsonify

BRequest

Crender_template

DFlask

Attempts:

3 left

💡 Hint

Common Mistakes

Importing Request instead of Flask

Using render_template which is for templates

Using jsonify which is for JSON responses

The Flask class is imported from the flask package to create the app instance.

2fill in blank

medium

Complete the command to run a Flask app using Gunicorn on port 8000.

Flask

gunicorn [1]:app -b 0.0.0.0:8000

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

Aapp.py

Bflask_app

Capp

Dmain

Attempts:

3 left

💡 Hint

Common Mistakes

Including the .py extension in the module name

Using a wrong module name that does not exist

Gunicorn expects the Python module name without the .py extension. If your file is app.py, you use 'app'.

3fill in blank

hard

Fix the error in the uWSGI command to serve the Flask app from app.py.

Flask

uwsgi --http :5000 --wsgi-file [1] --callable app

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

Aapp.py

Bapp

Cflask_app.py

Dmain.py

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the .py extension

Using a wrong filename

The --wsgi-file option requires the Python file name including the .py extension.

4fill in blank

hard

Fill both blanks to create a Gunicorn command that runs the app with 4 workers on port 8080.

Flask

gunicorn [1]:app -w [2] -b 0.0.0.0:8080

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

Aapp

B4

C2

Dmain

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong module name

Setting workers to a string instead of a number

The module name is 'app' and the number of workers is set to 4 with -w 4.

5fill in blank

hard

Fill all three blanks to create a uWSGI command that serves app.py with 2 processes and 4 threads on port 9090.

Flask

uwsgi --http :9090 --wsgi-file [1] --processes [2] --threads [3] --callable app

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

Aapp.py

B2

C4

Dapp

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting the .py extension

Confusing processes and threads values

Using the callable name in place of the file

The file is app.py, with 2 processes and 4 threads specified for uWSGI.

Practice

1. What is the main role of a WSGI server like Gunicorn or uWSGI when running a Flask application?

easy

A. To connect the Flask app to the web and handle multiple user requests efficiently

B. To write the Flask application code

C. To create the HTML templates for the Flask app

D. To manage the database connections directly

Solution

1. Step 1: Understand WSGI server purpose

   WSGI servers act as a bridge between the web and Flask app, managing requests.

2. Step 2: Identify what Gunicorn and uWSGI do

   They handle multiple users and serve the Flask app efficiently in production.

3. Final Answer:

   To connect the Flask app to the web and handle multiple user requests efficiently -> Option A

4. Quick Check:

   WSGI server role = Connect app and handle requests [OK]

Hint: WSGI servers link web and app, not write code [OK]

Common Mistakes:

• Thinking WSGI servers write app code
• Confusing WSGI with template engines
• Assuming WSGI manages databases

2. Which of the following is the correct command to start a Flask app using Gunicorn on port 8000?

easy

A. gunicorn app.py --port 8000

B. gunicorn run app --port=8000

C. gunicorn -w 4 -b 0.0.0.0:8000 app:app

D. gunicorn app:app --workers=2 --port=8000

Solution

1. Step 1: Recall Gunicorn syntax

   Gunicorn uses '-w' for workers and '-b' for binding address and port.

2. Step 2: Check correct app reference and port

   Correct format is 'gunicorn -w 4 -b 0.0.0.0:8000 app:app' to run app with 4 workers on port 8000.

3. Final Answer:

   gunicorn -w 4 -b 0.0.0.0:8000 app:app -> Option C

4. Quick Check:

   Gunicorn uses -w and -b flags [OK]

Hint: Gunicorn uses -w for workers and -b for bind address [OK]

Common Mistakes:

• Using --port instead of -b for binding
• Incorrect app reference like app.py instead of app:app
• Wrong flag order or missing workers

3. Given the command gunicorn -w 3 -b 127.0.0.1:5000 app:app, what will happen when you try to access the Flask app from another computer on the network?

medium

A. The app will be accessible from any computer on the network

B. The app will automatically bind to all interfaces

C. The app will refuse all connections and crash

D. The app will only be accessible from the local machine (127.0.0.1)

Solution

1. Step 1: Understand binding address 127.0.0.1

   Binding to 127.0.0.1 means the server listens only on localhost, not external network.

2. Step 2: Check network accessibility

   Other computers cannot access the app because it is not bound to the external IP or 0.0.0.0.

3. Final Answer:

   The app will only be accessible from the local machine (127.0.0.1) -> Option D

4. Quick Check:

   127.0.0.1 = localhost only [OK]

Hint: 127.0.0.1 binds only local access, not network [OK]

Common Mistakes:

• Assuming 127.0.0.1 allows network access
• Thinking Gunicorn auto-binds to all interfaces
• Confusing localhost with external IP

4. You run uwsgi --http :5000 --module app:app but get an error saying the module 'app' cannot be found. What is the most likely cause?

medium

A. The app.py file is missing or not in the current directory

B. The uWSGI command requires the --wsgi-file option instead of --module

C. The port 5000 is already in use by another process

D. The Flask app is not installed properly

Solution

1. Step 1: Understand module loading in uWSGI

   Using --module expects a Python module named 'app' with an 'app' variable inside.

2. Step 2: Check file presence and location

   If 'app.py' is missing or not in the current directory, uWSGI cannot find the module.

3. Final Answer:

   The app.py file is missing or not in the current directory -> Option A

4. Quick Check:

   Missing app.py causes module not found error [OK]

Hint: Check app.py file exists in current folder [OK]

Common Mistakes:

• Confusing --module with --wsgi-file
• Assuming port conflicts cause module errors
• Ignoring file location issues

5. You want to deploy a Flask app with uWSGI to handle 8 worker processes and bind it to all network interfaces on port 8080. Which command correctly achieves this?

hard

A. uwsgi --http 0.0.0.0:8080 --workers 8 --module app:app

B. uwsgi --http :8080 --processes 8 --module app:app --master

C. uwsgi --socket 0.0.0.0:8080 --processes 8 --wsgi-file app.py

D. uwsgi --http 127.0.0.1:8080 --workers 8 --module app:app

Solution

1. Step 1: Identify correct uWSGI flags for HTTP and workers

   --http :8080 binds to all interfaces on port 8080; --processes 8 sets 8 worker processes.

2. Step 2: Confirm module and master process usage

   --module app:app correctly points to the Flask app; --master enables master process for better management.

3. Step 3: Eliminate incorrect options

   A: uwsgi --http 0.0.0.0:8080 --workers 8 --module app:app uses invalid --workers flag (use --processes); B: uwsgi --http 127.0.0.1:8080 --workers 8 --module app:app binds only to localhost; C: uwsgi --socket 0.0.0.0:8080 --processes 8 --wsgi-file app.py uses --socket which is for socket mode, not HTTP.

4. Final Answer:

   uwsgi --http :8080 --processes 8 --module app:app --master -> Option B

5. Quick Check:

   Use --http :port and --processes with --master for production [OK]

Hint: Use --http :port and --processes with --master for uWSGI [OK]

Common Mistakes:

• Using --workers instead of --processes
• Confusing --socket with --http
• Binding only to 127.0.0.1 for network apps