Master Dockerfile & Docker‑Compose: Build Custom Images and Orchestrate Containers

Dockerfile Image Creation

In Docker or Podman, an image is the foundation of a container. While official images from Docker Hub meet basic needs, custom images are required for specific business requirements, and Dockerfile provides the configuration to build them.

Basic Instructions

Dockerfile consists of a series of instructions, each creating a new layer. Fewer instructions result in smaller images.

FROM ubuntu:20.04
LABEL version="1.0.0" maintainer="[email protected]"
ADD Django-3.2.5.tar.gz /opt/
COPY sources.list /etc/apt/sources.list
RUN apt update && apt install -y python3 python3-pip
WORKDIR /opt/
RUN mv django-3.2.5 django
WORKDIR /opt/django
RUN python3 setup.py install
WORKDIR /opt
RUN django-admin.py startproject djdemo
COPY run.sh /opt/djdemo/run.sh
WORKDIR /opt/djdemo
RUN sed -i "s/ALLOWED_HOSTS = \[\]/ALLOWED_HOSTS = ['*']/g" djdemo/settings.py && chmod 755 run.sh
EXPOSE 8000
CMD ["/bin/sh", "run.sh"]

Key instructions include:

FROM : specifies the base image (only one per Dockerfile).

LABEL : adds metadata such as version and maintainer.

RUN : executes shell commands; combine multiple commands with && or line continuation.

WORKDIR : sets the working directory inside the image.

ADD and COPY : copy files from the host into the image; ADD can also unpack archives.

ENV : defines environment variables.

EXPOSE : documents the port the container will listen on.

CMD : defines the default command to run when the container starts.

After writing the Dockerfile, build the image with: sudo docker build -t djdemo:3.2.5 . Run the container and map the internal port 8000 to host port 8008:

docker run -d -p 8008:8000 --name=django1 djdemo:3.2.5

Docker‑Compose Container Orchestration

Docker‑Compose allows you to define and run multi‑container applications using a single docker-compose.yml file. It groups services, networks, and volumes into a project.

Basic Usage

# docker-compose.yml (excerpt)
version: "3.8"
services:
  web1:
    image: nginx:1.21.4
    container_name: "web1"
    ports:
      - "8081:80"
    networks:
      - dev
  web2:
    image: nginx:1.21.4
    container_name: "web2"
    ports:
      - "8082:80"
    networks:
      - dev
      - pro
networks:
  dev:
    driver: bridge
  pro:
    driver: bridge

Common commands: docker-compose up – start all services (add -d to run in detached mode). docker-compose down – stop and remove containers, networks, and volumes. docker-compose ps – list running containers. docker-compose build – build images defined with build directives. docker-compose logs – view service logs.

Key configuration options include:

image and build – specify an existing image or a Dockerfile directory.

ports – map host ports to container ports (use string format to avoid YAML parsing issues).

environment – set environment variables inside the container.

depends_on – define startup order between services.

volumes – mount host directories or named volumes.

By defining services such as a web server, database, and cache in a single Compose file, you can launch a complete application stack with a single command.