Configure Docker to host the application

Docker is a popular way to distribute applications. Assuming that you've set all required dependencies in the setup.py, we're going to create an image with these properties:

  • Run by an unprivileged user: Create an unprivileged user with permissions to run our program.
  • Robust to vulnerabilities: Don't use Alpine as it's known to react slow to new vulnerabilities. Use a base of Debian instead.
  • Smallest possible: Use Docker multi build step. Create a builder Docker that will run pip install and copies the required executables to the final image.
FROM python:3.8-slim-buster as base

FROM base as builder

RUN python -m venv /opt/venv
# Make sure we use the virtualenv:
ENV PATH="/opt/venv/bin:$PATH"

COPY . /app
WORKDIR /app
RUN pip install .

FROM base

COPY --from=builder /opt/venv /opt/venv

RUN useradd -m myapp
WORKDIR /home/myapp

# Copy the required directories for your program to work.
COPY --from=builder /root/.local/share/myapp /home/myapp/.local/share/myapp
COPY --from=builder /app/myapp /home/myapp/myapp
RUN chown -R myapp:myapp /home/myapp/.local

USER myapp
ENV PATH="/opt/venv/bin:$PATH"
ENTRYPOINT ["/opt/venv/bin/myapp"]

If we need to use it with MariaDB or with Redis, the easiest way is to use docker-compose.

version: '3.8'

services:
  myapp:
    image: myapp:latest
    restart: always
    links:
      - db
    depends_on:
      - db
    environment:
      - AIRSS_DATABASE_URL=mysql+pymysql://myapp:supersecurepassword@db/myapp
  db:
    image: mariadb:latest
    restart: always
    environment:
      - MYSQL_USER=myapp
      - MYSQL_PASSWORD=supersecurepassword
      - MYSQL_DATABASE=myapp
      - MYSQL_ALLOW_EMPTY_PASSWORD=yes
    ports:
      - 3306:3306
    command:
      - '--character-set-server=utf8mb4'
      - '--collation-server=utf8mb4_unicode_ci'
    volumes:
      - /data/myapp/mariadb:/var/lib/mysql

The depends_on flag is not enough to ensure that the database is up when our application tries to connect. So we need to use external programs like wait-for-it. To use it, change the earlier Dockerfile to match these lines:

...

FROM base

RUN apt-get update && apt-get install -y \
    wait-for-it \
 && rm -rf /var/lib/apt/lists/*

...

ENTRYPOINT ["/home/myapp/entrypoint.sh"]

Where entrypoint.sh is something like:

#!/bin/bash

# Wait for the database to be up
if [[ -n $DATABASE_URL ]];then
    wait-for-it db:3306
fi

# Execute database migrations
/opt/venv/bin/myapp install

# Enter in daemon mode
/opt/venv/bin/myapp daemon

Remember to add the permissions to run the script:

chmod +x entrypoint.sh

Last update: 2020-07-14