Flask-MongoDB Web App Example

An example of a full-stack web application, built in Python with flask and pymongo.

Quick test drive

The fastest way to see the example app in action on your own computer is to use Docker.

First you must...

• install and run docker desktop
• create a dockerhub account

Option 1

Use Docker Compose to boot up both the mongodb database and the flask-app web app with one command:

• docker compose up --force-recreate --build ... add -d to run in detached/background mode.
• and then docker compose down in a separate terminal window to stop the containers when done.

If you see an error message that a particular port is already in use, select a different port for either the flask-app or mongodb service, as necessary. To do so, edit the first port number for that service in the docker-compose.yml file and try again. E.g., change the flask-app's port to 10000:5000 if you want the flask app to run on port 10000 on your computer. If changing the flask-app port in this way, you must also update the FLASK_PORT setting in the docker-compose.yml file to match.

View the app in your browser:

• open a web browser and go to http://localhost:5000 (or change 5000 to whatever port number you used for the flask-app.)

Note that you edit any of the files in the project, you will have to stop and then restart the containers, as indicated above.

Option 2

Alternatively, it is possible to boot up the flask-app separately from mongodb. Note that you will not be able to edit the app code when running it this way... instructions further below show you how to set up the app in a way that allows you to edit the code and see the changes.

Start up a MongoDB database first:

• run command, docker run --name mongodb_dockerhub -p 27017:27017 -e MONGO_INITDB_ROOT_USERNAME=admin -e MONGO_INITDB_ROOT_PASSWORD=secret -d mongo:latest

Start up the flask-app:

• run command, docker run -ti --rm -d -p 5000:5000 -e MONGO_DBNAME=flask-mongodb-web-app-example -e MONGO_URI="mongodb://admin:[email protected]:27017" bloombar/flask-mongodb-web-app-example
• if you see an error about the port number being already in use, change the first 5000 in the command to a different port number, e.g. -p 10000:5000 to use your computer's port 10000.

View the app in your browser:

• open a web browser and go to http://localhost:5000 (or change 5000 to whatever port number you used in the command above)

Setup for editing

The following instructions show you how to set up the example app on your own computer in a way that allows you to edit it.

Build and launch the database

If you have not already done so, start up a MongoDB database:

• run command, docker run --name mongodb_dockerhub -p 27017:27017 -e MONGO_INITDB_ROOT_USERNAME=admin -e MONGO_INITDB_ROOT_PASSWORD=secret -d mongo:latest

The back-end code will integrate with this database. However, it may be occasionally useful interact with the database directly from the command line:

• connect to the database server from the command line: docker exec -ti mongodb_dockerhub mongosh -u admin -p secret
• show the available databases: show dbs
• select the database used by this app: use example
• show the documents stored in the messages collection: db.messages.find() - this will be empty at first, but will later be populated by the app.
• exit the database shell whenever you have had your fill: exit

If you have trouble running Docker on your computer, use a database hosted on MongoDB Atlas instead. Atlas is a "cloud" MongoDB database service with a free option. Create a database there, and make note of the connection string, username, password, etc.

Create a .env file

A file named .env is necessary to run the application. This file contains sensitive environment variables holding credentials such as the database connection string, username, password, etc. This file should be excluded from version control in the .gitignore file.

An example file named env.example is given. Copy this into a file named .env and edit the values to match your database. If following the instructions and using Docker to run the database, the values should be:

MONGO_DBNAME=example
MONGO_URI="mongodb://admin:secret@localhost:27017/example?authSource=admin&retryWrites=true&w=majority"

The other values can be left alone.

pip

Note that most Python programs require the use of the package manager named pip - the default Python "package manager". A package manager is software that takes care of installing the correct version of any modules in the correct place for the current system you are running it on. It comes with most distributions of Python. On many machines, the Python 3-compatible version it is calld pip3 and on others it is simply pip... on some either works. If you are unsure, try both in the commands where you see it mentioned.

Set up a Python virtual environment

There are multiple ways to set up a Python virtual environment - a specific area of memory and disk space where you can install the dependencies and settings necessary to run a specific app in isolation from other apps on the same computer... here are instructions for using either pipenv or venv.

Using pipenv

The ability to make virtual environemnts with pipenv is relatively easy, but it does not come pre-installed with Python. It must be installed.

Install pipenv using pip:

pip3 install pipenv

Activate it:

pipenv shell

Your command line will now be running within a virtual environment.

The file named, Pipfile contains a list of dependencies - other Python modules that this app depends upon to run. These will have been automatically installed into the virtual environment by pipenv when you ran the command pipenv shell.

Using venv

If you refuse to use pipenv for some reason, you can use the more traditional venv instead. The ability to make virtual environments with venv comes included with standard Python distributions.

This command creates a new virtual environment with the name .venv:

python3 -m venv .venv

To activate the virtual environment named .venv...

On Mac:

source .venv/bin/activate

On Windows:

.venv\Scripts\activate.bat

The pip settings file named, requirements.txt contains a list of dependencies - other Python modules that this app depends upon to run.

To install the dependencies into the currently-active virtual environment, use pip:

pip3 install -r requirements.txt

Run the app

• define two environment variables from the command line:
  • on Mac, use the commands: export FLASK_APP=app.py and export FLASK_ENV=development.
  • on Windows, use set FLASK_APP=app.py and set FLASK_ENV=development.
• start flask with flask run - this will output an address at which the app is running locally, e.g. https://127.0.0.1:5000. Visit that address in a web browser.
• in some cases, the command flask will not be found when attempting flask run... you can alternatively launch it with python3 -m flask run --host=0.0.0.0 --port=5000 (or change to python -m ... if the python3 command is not found on your system).

Note that this will run the app only on your own computer. Other people will not be able to access it. If you want to allow others to access the app running on your local machine, try using the flask-ngrok module.