Continuing with the docker articles, this time we will talk about starting two containers where one serves the other: one container will run the redis service and the other will be a simple web application made with flask.

To manage several containers there is docker-compose; for this article, you can check the link about docker-compose with flask at the following link.

The previous articles that cover docker are:

  1. Install Docker on Debian Jessie
  2. Using Docker on Debian Jessie (part 1)
  3. Using Docker on Debian Jessie (part 2)
  4. Create a Docker image with a Dockerfile
  5. Starting Django using Docker
  6. Starting Gitlab using Docker

First, create the working directory.

mkdir flask
cd flask

Create the file app.py with the following content:

#Se importa flask y redis
from flask import Flask
from redis import Redis

#Se crea la instancia de flask 
app = Flask(__name__)
#Se crea la instancia de redis
redis = Redis(host="redis",port=6379)


#Se crea la función hello definiendo la ruta del decorador.
@app.route("/")
def hello():
    #Se incrementa el valor de la variable hits de redis
    redis.incr('hits')
    #Se retorna un mensaje con el valor actual de la variable en redis
    return "Hello is me %s...\n" %redis.get('hits')


if __name__ == "__main__":
    #Se ejecuta la aplicación en modo debug
    app.run(host="0.0.0.0",debug=True)

Create the file requerimientos.txt, which defines that flask and redis need to be installed:

flask
redis

Create the Dockerfile file with the following content:

FROM python:2.7
WORKDIR /code
ADD requerimientos.txt /code/
RUN pip install -r requerimientos.txt
ADD . /code
CMD python app.py

Build the web image:

docker build -t web .

The services are defined through the docker-compose.yml file, which contains the following:

web:
  build: .
  ports:
   - "5000:5000"
  volumes:
   - .:/code
  links:
   - redis
redis:
  image: redis

Description of the docker-compose.yml file: web: Defines the image called web to be built; it handles ports, local 5000 and external will also be 5000; the volume directory called code is also defined, and finally for web, links is defined, which calls the redis image. redis: Defines the redis image. Build and run the application with compose:

From the directory where the files are located, run:

docker-compose up

The following figure shows that the application is running:

Opening the browser at localhost:5000 gives what the following figure shows:

Running docker ps lists the containers that are running:

docker-compose also has the ps command, and it gives the following:

The output is simplified compared to docker ps.

To stop the processes or the execution of the service, use docker-compose's stop command:

docker-componse stop

With docker compose you can run multiple images and use them in a main application, which achieves the concept of microservices.

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