Python WSGI Examples

A starter project for Clark's Databases course (CSCI 220). This project includes a web server and database.

WARNING: These examples are intended to illustrate the basics of web application programming. The examples are vulnerabile to attacks like cross site scripting. Eventually, we will introduce frameworks like Django which incorporate protections against many common attacks.

Follow these steps to get started:

Step 0: Clone This Repository

Unless otherwise specified, all commands mentioned below should be run within the root directory of this repository.

Step 1: Install Docker

This project includes several components:

• uWSGI, which will run your Python code
• NGINX, a web server which will allow browsers to communicate with uWSGI
• PostgresSQL, a database which will store your application's persistent data

It could be time-consuming to install and configure all of these on your computer, but thankfully there is a better way: Docker! Install Docker, and it will be easy to run all of these components.

Step 2: Configure Database Password

It is a terrible idea to run software with default passwords. To configure the password for the database, you will need to write them in a .env file. Follow these steps:

1. Copy dot_env_example to .env
2. Run chmod 600 .env to prevent other users from reading your .env file
3. Edit .env, changing the text RANDOM_PASSWORD to a password which is actually random

Step 3: Start the Docker Services

Run:

docker compose up

The first time you run it, this command will take a few minutes to complete. This is because Docker needs to download the code for PostgresSQL, etc.

When you are done running the application, you can stop it by typing Control-C.

Step 4: Load the Application

Load http://localhost and you should see "Hello World".

Step 5: Running a Different Application

To run an application other than hello_world.py, simply edit UWSGI_FILE in your .env, then recreate the containers by running docker compose up.

Hints

• Each time you edit your code, you will need to restart the uwsgi service. You can do this by either interrupting docker compose up by typing Control-C, or you can simply restart uwsgi with docker compose restart uwsgi.
• Print statements and fatal exceptions will be logged to the uwsgi.log file. Refer to this file when debugging your code.
• If you want to add CSS files or other static resources, you should store them in the /static directory. The nginx service will serve these resources.
• To interactively run SQL commands, run:

> docker compose exec postgres bash
# psql --username="$POSTGRES_USER" --dbname="$POSTGRES_DB"

• To execute SQL commands from a file, run:

> docker compose exec postgres bash
# psql --username="$POSTGRES_USER" --dbname="$POSTGRES_DB" --set ON_ERROR_STOP=on --file /postgres_files/db_dump.DATE.sql

• To dump the SQL commands needed to recreate a database to file, run:

> docker compose exec postgres bash
# pg_dump --username="$POSTGRES_USER" --dbname="$POSTGRES_DB" --file=/postgres_files/db_dump.DATE.sql

References

WSGI Tutorial