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Docker

Working with Docker

Stopping Docker

To stop the service-container, but not destroy it (often sufficient for day-to-day work):

docker-compose stop

To stop and destroy the service container:

docker-compose down

Add the -v flag to destroy the data volumes as well:

docker-compose down -v

Recycling / Refreshing Database

To restore a database to its original state and remove any data manually added, delete the container and image. From Docker:

docker-compose down -v
  1. Open Containers section
  2. Delete people-db-1 container
  3. Open Images Tab
  4. Remove djangorestapipostrgresql image

Cache mount

This helps speed up subsequent docker builds by caching intermediate files and reusing them across builds. It's available with docker buildkit. The key here is to disable anything that could delete the cache, because we want to preserve it. The cache mount is not going to end up in the docker image being built, so there's no concern about disk space usage.

Put this flag between RUN and the command

RUN \
--mount=type=cache,target=/root/.cache
  pip install -r requirements.txt

For pip, the files are by default stored in /root/.cache/pip. Pip caching docs

For apk, the cache directory is /var/cache/apk/. APK wiki on local cache

For apt, the cache directory is /var/cache/apt/.

References

Alpine vs Debian based images

We're choosing to use an Alpine-based image for the smaller size and faster builds and downloads. However, a Debian-based image has the advantage of a large ecosystem of available packages, a limitation of Alpine that we may run up against in the future.

Switching to Debian

Here is how we can switch to a Debian-based images if we need to:

  1. Edit Dockerfile to look something like this

    app/Dockerfile
    # pull official base image
FROM python:3.10-alpine
# (1)! define base image
FROM python:3.10-bullseye

# set work directory
WORKDIR /usr/src/app

# set environment variables
ENV PYTHONDONTWRITEBYTECODE=1
ENV PYTHONUNBUFFERED=1
ENV PYTHONPYCACHEPREFIX=/root/.cache/pycache/
ENV PIP_CACHE_DIR=/var/cache/buildkit/pip

RUN mkdir -p $PIP_CACHE_DIR
# (2)! prevent cache deletion
RUN rm -f /etc/apt/apt.conf.d/docker-clean; \ 
echo 'Binary::apt::APT::Keep-Downloaded-Packages "true";' > /etc/apt/apt.conf.d/keep-cache

# install system dependencies
RUN \
  --mount=type=cache,target=/var/cache/apk \ 
  --mount=type=cache,target=/etc/apk/cache \ 
  apk add \czjqqkd:19
  'graphviz=~9.0'

# install font for graphviz
COPY Roboto-Regular.ttf /root/.fonts/
RUN fc-cache -f
# (3)! define cache mounts and install dependencies
  --mount=type=cache,target=/var/cache/apt,sharing=locked \ 
  --mount=type=cache,target=/var/lib/apt,sharing=locked \ 
  apt-get update \ 
  && apt-get install --no-install-recommends -yqq \ 
  netcat=1.10-46 \ 
  gcc=4:10.2.1-1 \ 
  postgresql=13+225+deb11u1 \ 
  graphviz=2.42.2-5

# install dependencies
COPY ./requirements.txt .
# hadolint ignore=DL3042
# (4)! install uv for faster dependency resolution
RUN \
  --mount=type=cache,target=/root/.cache \
  pip install uv==0.1.15 \
  && uv pip install --system -r requirements.txt

# copy entrypoint.sh
COPY ./entrypoint.sh .
RUN sed -i 's/\r$//g' /usr/src/app/entrypoint.sh \
  && chmod +x /usr/src/app/entrypoint.sh

# copy project
COPY . .

# run entrypoint.sh
ENTRYPOINT ["/usr/src/app/entrypoint.sh"]
    1. define base image
    2. prevent cache deletion
    3. install system dependencies
      1. define cache mounts for apt and lib
      2. install netcat for db wait script, which is used in entrypoint.sh
      3. install gcc for python local compiling, which shouldn't be needed
      4. install postgresql for dbshell management command
      5. install graphviz for generating ERD in erd.sh
    4. install uv for faster dependency resolution, which may or may not be wanted

  2. Use the dive tool to check the image layers for extra files that shouldn't be there.