Run a docker container from an existing container using docker-py

Question

I have a Docker container which runs a Flask application. When Flask receives and http request, I would like to trigger the execution of a new ephemeral Docker container which shutdowns once it completes what it has to do.

I have read Docker-in-Docker should be avoided so this new container should be run as a sibling container on my host and not within the Flask container.

What would be the solution to do this with docker-py?

What have you tried already? Do you have some sample code and something like a `docker-compose.yml` or a `docker run` command for the main service you can share? — David Maze, Aug 12 '18 at 14:19
I haven't tried anything yet as I'm not very sure how to start on this. I'll update my answer with what I have in mind. — Alexis.Rolland, Aug 12 '18 at 15:44

score 10 · Answer 1 · answered Aug 12 '18 at 15:22

10

we are doing stuff like this by mounting docker.sock as shared volume between the host machine and the container. This allows the container sending commands to the machine such as docker run

this is an example from our CI system:

 volumes:
 - /var/run/docker.sock:/var/run/docker.sock

answered Aug 12 '18 at 15:22

gCoh

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I read about this indeed but would mounting docker socket in my Flask container be enough to run a sibling container with docker-py? – Alexis.Rolland Aug 12 '18 at 15:45
1

Yes, with this you can control docker as if you're on the host – Erwan Aug 12 '18 at 16:06
1

(...and remember that you can control the host as any other user that can run Docker commands can.) – David Maze Aug 12 '18 at 16:30

Alexis.Rolland · Accepted Answer · 2018-08-13T23:23:39.567

Answering my own question. Here is a complete setup which works. In one folder, create the following files:

requirements.txt
Dockerfile
docker-compose.yml
api.py

requirements.txt

docker==3.5.0
flask==1.0.2

Dockerfile

FROM python:3.7-alpine3.7


# Project files
ARG PROJECT_DIR=/srv/api
RUN mkdir -p $PROJECT_DIR
WORKDIR $PROJECT_DIR
COPY requirements.txt ./

# Install Python dependencies
RUN pip install --upgrade pip
RUN pip install -r requirements.txt

docker-compose.yml

Make sure to mount docker.sock in volumes as mentioned in the previous answer above.

version: '3'
services:
  api:
    container_name: test
    restart: always
    image: test
    build:
      context: ./
    volumes:
      - ./:/srv/api/
      - /var/run/docker.sock:/var/run/docker.sock
    environment:
      FLASK_APP: api.py
    command: ["flask", "run", "--host=0.0.0.0"]
    ports:
      - 5000:5000

api.py

from flask import Flask
import docker
app = Flask(__name__)


@app.route("/")
def hello():
    client = docker.from_env()
    client.containers.run('alpine', 'echo hello world', detach=True, remove=True)
    return "Hello World!"

Then open your browser and navigate to http://0.0.0.0:5000/

It will trigger the execution of the alpine container. If you don't already have the alpine image, it will take a bit of time the first time because Docker will automatically download the image.

The arguments detach=True allows to execute the container asynchronously so that Flask does not wait for the end of the process before returning its response.

The argument remove=True indicates Docker to remove the container once its execution is completed.

Run a docker container from an existing container using docker-py

2 Answers2