Steps to set up Pipenv, create a CRUD app with Flask, and containerize it with Docker

Background of writing the article

I will retire from my current SIer this month, and I am thinking of becoming an engineer around infrastructure. When building an infrastructure and CI / CD environment that makes full use of the public cloud in recent years, even a legacy engineer like me should avoid building apps in various languages or creating apps for communication confirmation. It is around this time that I feel that I can no longer pass.

I wanted to do my best to build various languages and make a little web application, so this time I described the procedure to create a Flask application (just touching it) with Python and Pipenv and make it a Docker container.

Installing Pipenv

In recent years, Python environment construction seems to be built using a tool called Pipenv, so I tried using it. It's like JavaScript npm and easy to use.

pip install pipenv

Creating an app project

mkdir flask-app
cd flask-app

This time I will use Python 3.8.

pipenv --python 3.8
pipenv install flask
pipenv install --dev autopep8

Create an empty file to be created.

mkdir src
touch src/main.py
touch Dockerfile
touch .dockerignore

Add to the scripts section of the Pipfile.

[scripts]
start = "python src/main.py"

Flask application coding

It will be a code written by a Python amateur, but I created it like the following.

src/main.py


import sqlite3
import flask

app = flask.Flask(__name__)


def get_db():
    db = getattr(flask.g, '_database', None)
    if db is None:
        db = flask.g._database = sqlite3.connect('mydb.sqlite')
    return db


@app.teardown_appcontext
def close_conn(exception):
    db = getattr(flask.g, '_database', None)
    if db is not None:
        db.close()


@app.route('/todos/<id>', methods=['GET'])
@app.route('/todos', methods=['GET', 'POST'])
def todos(id=None):
    db = get_db()

    #Create a table when you receive a request
    curs = db.cursor()
    curs.execute(
        'create table if not exists todos('
        'id integer primary key autoincrement, title string)'
    )

    id = flask.request.values.get('id', id)

    if flask.request.method == 'GET' and id is not None:
        curs.execute('select * from todos where id = {}'.format(id))
        response = curs.fetchone()
        if response is not None:
            id, title = response
            return flask.jsonify(todo={"id": id, "title": title}), 200

        return flask.jsonify(message='resource not found'), 400

    if flask.request.method == 'GET':
        curs.execute('select * from todos')
        response = curs.fetchall()
        todos = []
        for todo in response:
            id, title = todo
            todos.append({"id": id, "title": title})

        return flask.jsonify(todos=todos), 200

    if flask.request.method == 'POST':
        title = flask.request.json['title']
        curs.execute('insert into todos(title) values("{}")'.format(title))
        db.commit()
        return flask.jsonify(message='created new toto')


def main():
    app.debug = True
    app.run(host='0.0.0.0', port=5000)


if __name__ == "__main__":
    main()

At this point it should work in your local environment.

pipenv run start

 * Serving Flask app "main" (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: on
 * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)
 * Restarting with stat
 * Debugger is active!
 * Debugger PIN: 208-926-045

Hit the curl command to check.

curl -XPOST -H 'Content-Type: application/json' localhost:5000/todos -d '{"title": "new task1"}'
curl -XPOST -H 'Content-Type: application/json' localhost:5000/todos -d '{"title": "new task2"}'
curl localhost:5000/todos
curl localhost:5000/todos/1

Creating and building a Dockerfile

I don't know the practice when combined with Pipenv, but I made it with Simple Is Best.

FROM python:3.8

ENV LC_ALL=C.UTF-8 \
    LANG=C.UTF-8

WORKDIR /app
COPY . .

RUN pip install pipenv
RUN pipenv install

CMD ["pipenv", "run", "start"]

EXPOSE 5000

Also create a .dockerignore file.

.dockerignore


*.sqlite
.git

Build.

docker image build -t flaskapp:latest . 

Start the container (starting the local port as 15000).

docker container run -it -p 15000:5000 --rm flaskapp:latest

 * Serving Flask app "main" (lazy loading)
 * Environment: production
   WARNING: This is a development server. Do not use it in a production deployment.
   Use a production WSGI server instead.
 * Debug mode: on
 * Running on http://0.0.0.0:5000/ (Press CTRL+C to quit)
 * Restarting with stat
 * Debugger is active!
 * Debugger PIN: 954-331-726

It's OK if you can confirm by hitting the curl command.

curl -XPOST -H 'Content-Type: application/json' localhost:15000/todos -d '{"title": "new task1"}'
curl -XPOST -H 'Content-Type: application/json' localhost:15000/todos -d '{"title": "new task2"}'
curl localhost:15000/todos
curl localhost:15000/todos/1

in conclusion

I was accustomed to npm and yarn with nodejs, so I avoided building a python environment, but I found Pipenv useful. I didn't know Pipenv, so I felt like I had lost it.

For the time being, from the perspective of an infrastructure engineer (subjective), I'm satisfied because I've done so far. We will do our best to provide the environment without bothering the application engineer.

However, although I didn't remember much until about five years ago, the changes in the environment surrounding IT technology these days are tremendous. It has been left behind, but I am desperately trying to catch up with it.

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