Docker Compose

Docker Compose

Tool for defining and running multi container applications. Simplifies the control of your entire application stack, making it easy yo manage servicess, networks and volumes in a single YAML configuration file

File name: compose.yaml

Commands

• docker compose up: To start all the services
• docker compose down: To stop and remove all the running containers
• docker container logs: To monitor the output of the running container
• docker compose ps: List all the services along with the status
• docker compose stop: To stop all the running services
• docker compose start: To start all the running services
• docker compose down –volumes: To delete volumes also

compose.yaml file

The docker compose file is written in YAML[YAML Ain’t Markup Language] format.

ervices:
  web:
    build: .
    ports:
      - "8000:5000"
  redis:
    image: "redis:alpine"

• Services: Used to specify all of the containers the application need to run
• we can use any name for the service but it is better to use name based on the service it is providing example: frontend, backend, database, etc.

Variables

.env file

An .env file in Docker Compose is a text file used to define variables that should be made available for interpolation when running docker compose up. This file typically contains key-value pairs of variables, and it lets you centralize and manage configuration in one place. The .env file is useful if you have multiple variables you need to store.

The .env file is the default method for setting variables. The .env file should be placed at the root of the project directory next to your compose.yaml file.

Need to mention  file like this in compose.yaml file if .env file in different path
 
env_file:
 - ./BackEnd/config.env

• The following syntax rules apply to environment files:
• Lines beginning with # are processed as comments and ignored.
• Blank lines are ignored.
• Unquoted and double-quoted (") values have interpolation applied.
• Each line represents a key-value pair. Values can optionally be quoted.
  • VAR=VAL -> VAL
  • VAR="VAL" -> VAL
  • VAR='VAL' -> VAL
• Inline comments for unquoted values must be preceded with a space.
  • VAR=VAL # comment -> VAL
  • VAR=VAL# not a comment -> VAL# not a comment
• Inline comments for quoted values must follow the closing quote.
  • VAR="VAL # not a comment" -> VAL # not a comment
  • VAR="VAL" # comment -> VAL
• Single-quoted (') values are used literally.
  • VAR='$OTHER' -> $OTHER
  • VAR='${OTHER}' -> ${OTHER}
• Quotes can be escaped with \.
  • VAR='Let\'s go!' -> Let's go!
  • VAR="{\"hello\": \"json\"}" -> {"hello": "json"}
• Common shell escape sequences including \n, \r, \t, and \\ are supported in double-quoted values.

If you create a file with another name like compose.env in current directory but want to use in runtime you can pass the file while running command

docker compose --env-file compose.env down || true
docker compose --env-file compose.env pull
docker compose --env-file compose.env up -d

We can also define variables directly in compose.yaml file

services:
    webapp:
      image: my-webapp-image
      environment:
        - DEBUG=${COMPOSE_DEBUG}

Declare volumes

services:
  mongodb:
    image: mongo:4.4
    command: [--bind_ip_all]
    volumes:
      - mongo-data:/data/db
volumes:
  mongo-data:

• Here mongo-data is the named volume that we have created.
• mongo-data is in host and /data/db is container path.

Exposing ports

services:
  frontend:
    image: "${FRONTEND_IMAGE}"
    ports:
      - "3000:80"
    networks:
      - mynetwork

• Here we use ports: to assign port
• 3000 is host port and 80 is container port

Examples:

To deploy a word press site

.env file

MYSQL_ROOT_PASSWORD=root@123
MYSQL_DATABASE=mydb
MYSQL_USER=dipen
MYSQL_PASSWORD=password
 
 
TAG=8.0.42-oraclelinux9

compose.yaml file

services:
  scheduler:
    build: scheduler/.
    ports:
      - "8000:80"
    depends_on:
      - database
  storefront:
    build: storefront/.
    ports:
      - "8001:80"
    depends_on:
      - database
  database:
    image: "mysql:${TAG}"
    environment:
      MYSQL_ROOT_PASSWORD: ${MYSQL_ROOT_PASSWORD}
      MYSQL_DATABASE: ${MYSQL_DATABASE}
      MYSQL_USER: ${MYSQL_USER}
      MYSQL_PASSWORD: ${MYSQL_PASSWORD}
    volumes:
      - ./mysql:/docker-entrypoint-initdb.d:ro
      - kineteco:/var/lib/mysql
volumes:
  kineteco:

• This is the format to create a compose.yaml file and .env file.