Docker-Compose

Running a multi-container application

# Build images
docker-compose build
# Start services (containers)
docker-compose up -d
# Stop and remove containers created by up
docker-compose down
# Logs
docker-compose logs -f [service name]
# List containers
docker-compose ps
# Execute a command in a container
docker-compose exec [service name] [command]
# List images
docker-compose images

The docker-compose.yaml file can have the following top-level elements:

• services - list of all containers to be started;
• networks - list of subnets that unite groups of containers into a virtual local network;
• volumes - list of volumes that will be available to the containers described in the configuration file;
• configs - list of parameters that allow containers to be run in different modes without rebuilding them;
• secrets - list of security-sensitive parameters.

Example 1 (web server and DB)

compose.yml

version: "3.9"
services:
  # MySQL image
  db:
    # Specify platform
    platform: linux/amd64
    # Image must be stored locally or in a registry
    image: mysql:5.7
    # Volume mount paths
    volumes:
      # Data volume specified at the end
      - db_data:/var/lib/mysql
    # Automatically restart on stop
    restart: always
    # Set environment variables
    environment:
      MYSQL_ROOT_PASSWORD:
      MYSQL_DATABASE: wordpress
      MYSQL_USER: wordpress
      MYSQL_PASSWORD:

  # WordPress image
  wordpress:
    depends_on:
      - db
    image: wordpress:latest
    # Port mapping
    ports:
      - "8000:80"
    restart: always
    environment:
      WORDPRESS_DB_HOST: db:3306
      WORDPRESS_DB_USER: wordpress
      WORDPRESS_DB_PASSWORD:
      WORDPRESS_DB_NAME: wordpress

volumes:
  db_data: {}

Start with docker-compose up

Example 2

• docker-compose.yml
• server/ - server files
• server/server.py - server code
• server/index.html - text to display
• server/Dockerfile - instructions for creating the server environment
• client/ - application files
• client/client.py - client code
• client/Dockerfile - instructions for creating the client environment

docker-compose.yml

# docker-compose file starts with the version tag
version: "3"
# docker-compose works with services
# 1 service = 1 container
services:
 # Creating two services
 # Name of the first service (container) is 'server'
 server:
   # Path to the Dockerfile for building the image
   build: server/
   # Run the command "python ./server.py"
   command: python ./server.py
   # Port mapping: [host port]:[container port]
   ports:
     - 1234:1234
 # Name of the second service (container) is 'client'
 client:
   # Path to the Dockerfile for building the image
   build: client/
   # Run the command "python ./client.py"
   command: python ./client.py
   # 'network_mode' to describe the network type
   # Specifies that the container can access the host's 'localhost'
   network_mode: host
   # 'depends_on' waits for other services before starting
   # Ensures the 'client' service waits for the 'server' service to be ready
   depends_on:
     - server

server/server.py

#!/usr/bin/env python3
# Import standard Python libraries
# Installed with Python
import http.server
import socketserver
# Variable for handling client requests to the server
handler = http.server.SimpleHTTPRequestHandler
# The server starts on port 1234
# This information is useful when working with docker-compose
with socketserver.TCPServer(("", 1234), handler) as httpd:
# The server will run continuously, waiting for client requests
httpd.serve_forever()

server/index.html

<h1>Some text</h1>

server/Dockerfile

# Import the base image
FROM python:latest
# Set the working directory for commands
WORKDIR /server/
# Import 'server.py' and 'index.html'
ADD server.py .
ADD index.html .

client/client.py

#!/usr/bin/env python3
# Import standard Python libraries
# Used to download 'index.html' from the server
# Installed with Python
import urllib.request
# Request variable for 'http://localhost:1234/'
fp = urllib.request.urlopen("http://localhost:1234/")
# 'encodedContent' is the encoded server response ('index.html')
# 'decodedContent' is the decoded server response (what we want to print)
encodedContent = fp.read()
decodedContent = encodedContent.decode("utf8")
# Print the contents of the file from the server ('index.html')
print(decodedContent)
# Close the connection to the server
fp.close()

client/Dockerfile

FROM python:latest
# Set the working directory '/client/'
WORKDIR /client/
# Import 'client.py' into '/client/'
ADD client.py .