11_DockerCompose_Orchestration

Docker compose

• Docker-compose is used to run multiple containers in a cluster that are dependent on each other. It is an alternative to Docker Swarm and Kubernetes but generally used for preferably small clusters.

• All the containers to be used are defined together in a configuration file called docker-compose.yaml

• YAML - Yet Another Markup Language

Example: Docker-Compose.yaml file

web:
  build: .
  links:
    - redis
  ports:
    - "3000"
    - "8000"

redis:
  image: redis:alpine
  volumes:
    - /var/redis/data:/data

Explanation: Here we launch a NodeJS web application connected to Redis database.

• Format is

container_name:
  property:
    - value

• First container called web is defined and uses a Dockerfile of NodeJS in the build path . (current folder)

• Dockerfile for NodeJS application

FROM ocelotuproar/alpine-node:5.7.1-onbuild
EXPOSE 3000

• links keyword is used to link one container in the yaml to another, it can be anything but it must be defined as a container name in the same file.

• Second container is of key-value database called Redis

• It is defined using Redis image from DockerHub

• Volume is mapped from the linked Node.JS container to the current container.

Docker-compose commands

• Launch the cluster

$ docker-compose up -d # for detached mode

• Check the state of containers in the cluster

$ docker-compose ps

• Check logs of the cluster

$ docker-compose logs

• Scale up/down a specific cluster of the container

$ docker-compose scale [container-name]=replicals [container-name]=replicas ...

• Stop all the containers of the cluster

$ docker-compose stop

• Remove all containers of the cluster

$ docker-compose rm