Docker-Compose

Faeshal.

14-12-2021

Docker File

Before we talk about compose one thing should we know is Docker Fie . What is Docker File ? . A Dockerfile is file that Docker reads from top to bottom. It contains a bunch of instructions which informs Docker HowDocker image should get built. Short Answer Dockerfile basically for Customize your Docker image .

You can relate it to cooking. In cooking you have recipes. A recipe lets you know all of the steps you must take in order to produce whatever you’re trying to cook. Recipe = Docker FIle

Docker File Command

Commands:
  FROM              Must be the first , for set base image container
  EXPOSE            For exposing container PORT
  RUN               Execute any commands in a new layer on top of the current image   CMD               For Executing Container
  LABEL             instruction adds metadata to an image
  ENV               sets the environment variable to the value
  COPY              copies new files or directories from <src>
  ADD               copies new files too but ADD have little power than copy , ADD supports 2 other sources. URL & TAR files
  ENTRYPOINT        allows you to configure a container that will run as an executable
  VOLUME            Create Container Volume
  USER              Sets the user name (or UID) and optionally the user group (or GID)
  WORKDIR           Sets the working directory for any RUN, CMD, ENTRYPOINT, COPY and ADD instructions
  ARG               defines a variable that users can pass at build-time to the builder
  HEALTHCHECK       tells Docker how to test a container to check that it is still working
  SHELL             allows the default shell used for the shell form of commands to be overridden
  ONBUILD           adds to the image a trigger instruction to be executed at a later time, when the image is used as the base for another build.
  STOP SIGNAL       sets the system call signal that will be sent to the container to exit

Create Docker FIle

Ok Let’s Practice, for example we have a Use Case:

you wanna build Node on top of Linux Alpine
Expose port 4000
Adding custom work directory to /app
Adding tini for graceful shutdown before you running it.

Answer :

FROM node:10.17-alpine

EXPOSE 4000

RUN apk add --no-cache tini

WORKDIR /app

COPY package*.json ./

RUN npm install && npm cache clean --force

COPY . .

ENTRYPOINT ["/sbin/tini", "--"]

CMD ["node","app.js"]

After that you ready to build the docker file by run

Docker build -t.

Very Simple Right ? It is ! . That’s why Developer & Operaion Team love Docker.

Docker Compose

What the heck is compose ? If you wanna run multiple container at single service (in local environment) you need compose . Short Answer compose is YAML file for defining multi container such as port , shared volume , relation between container etc.

YAML - Reference

Compose Command

Docker Compose CLICommands:

build              Build or rebuild services
bundle             Generate a Docker bundle from the Compose file
config             Validate and view the Compose file
create             Create services
down               Stop and remove containers, networks, images, and volumes
events             Receive real time events from containers
exec               Execute a command in a running container
help               Get help on a command
images             List images
kill               Kill containers
logs               View output from containers
pause              Pause services
port               Print the public port for a port binding
ps                 List containers
pull               Pull service images
push               Push service images
restart            Restart services
rm                 Remove stopped containers
run                Run a one-off command
scale              Set number of containers for a service
start              Start services
stop               Stop services
top                Display the running processes
unpause            Unpause services
up                 Create and start containers
version            Show the Docker-Compose version information

Create Docker Compose

The most important things you need to know, you must write docker compose YAML version in first line , There are two version now . Version 2 for local development and Version 3 if you using orchestration like kubernetes or swarm . I recomend you using version 2 because have a lot of feature for local development.

Docker Compose Version - Docs

Remember Docker Compose care about Indentation and case sensitive

Back To the create docker compose , for example we have use case :

You have 2 services , first app service and second mongo services which is your database
App services is build from docker file , so you no need to download image again.
Expose your app to port 3000 & make sure node app run after mongodb up and running
you need set MongoDB Volume too and expose mongo port to 27019

Answer :

version: '2.4'
services:
  app:
    restart: always
    build: .
    ports:
      - '3000:3000'
    depends_on:
      - mongo
  mongo:
    image: mongo:4.2.0
    ports:
      - '27018:27017'
    volumes:
      - mloandata:/data/db
      - mloanconfig:/data/configdb
volumes:
  mloandata:
  mloanconfig:

Last Word

That’s it about docker compose hope you will get better understanding about compose workflow, dont forget to check really good blog post about docker & compose , Link down below.