docker compose up

Docker Compose is a tool used to define and run multi-container Docker applications using a simple YAML file docker-compose.yml It lets you start, stop, and manage multiple containers (like app + database + cache) with a single command (docker compose up), making development and deployment easier.

version: "3.8"

services:
  flask-app:
    build: . #path to dockerfile
    #to use existing image use image tag like in db and give path to image.
    ports:
      - "5000:5000"
    environment:
      - MYSQL_HOST=db
      - MYSQL_USER=root
      - MYSQL_PASSWORD=rootpassword
      - MYSQL_DB=flaskdb
    depends_on:
      - db
    networks:
      - app-network

  db:
    image: mysql:8.0
    restart: always
    environment:
      - MYSQL_ROOT_PASSWORD=rootpassword
      - MYSQL_DATABASE=flaskdb
    volumes:
      - mysql-data:/var/lib/mysql
    networks:
      - app-network

volumes:
  mysql-data:

networks:
  app-network:
    driver: bridge

1. Healthchecks

A way to tell its status beyond just ‘is it running’

You define a healthcheck using the HEALTHCHECK instruction in a Dockerfile or inside a docker-compose.yml. Docker then:

Periodically runs the healthcheck command inside the container.
Marks the container as:
- healthy
- unhealthy
- starting (during initial delay or first checks)

db:
  image: mysql:8.0
  environment:
    - MYSQL_ROOT_PASSWORD=rootpassword
    - MYSQL_DATABASE=flaskdb
  healthcheck:
    test: ["CMD", "mysqladmin", "ping", "-h", "localhost"]
    interval: 10s
    timeout: 5s
    retries: 3

test: The command to check health (mysqladmin ping checks if MySQL is accepting connections).
interval: How often to run the check (every 10 seconds).
timeout: Max time to wait before considering the check failed (5 seconds).
retries: If it fails 3 times in a row, the container is marked unhealthy.

1. Healthchecks#

1. Healthchecks