What’s new in Docker Compose v3

Image Source & Credits: http://blog.terranillius.com/post/composev3_swarm/

In this blog, we’ll discuss new features added in Docker Compose v3. Docker compose added the feature of stack deployment with swarm.

To achieve this, we need to create a file named, docker-stack.yml and specify the deploy key, which would allow you to specify various properties of a swarm deployment in docker-stack.yml file.

For deploying this, you simply need to run the docker-stack deploy command with this docker-stack.yml file to pull the referenced images and launch the services in a swarm as configured in the .yml.

deploy key

The deploy key allows you to specify configuration related to the deployment and running of services. The deploy key can also be used to constrain some services to run only on the manager node.

Specify configuration related to the deployment and running of services. This only takes effect when deploying to a swarm cluster with `docker stack deploy` command and is ignored by docker-compose up and docker-compose run commands.

deploy:
  mode: replicated
  replicas: 5
  update_config:
    parallelism: 2
    delay: 10s
  restart_policy:
    condition: on-failure

Several sub-options available are mentioned below:

mode

mode is specified either as global (exactly one container per swarm node) or replicated (a specified number of containers). Default is replicated.

mode: global

replicas

To specify the number of containers that should be running at any given time.

replicas: 5

placement

To specify the placement constraints.

placement:
  constraints:
    - node.role == manager
    - engine.labels.operatingsystem == ubuntu 16.04

update_config

To configure how the service should be updated. Useful for configuring rolling updates.

• parallelism: The number of containers to update at a time.
• delay: The time to wait between updating a group of containers.
• failure_action: What to do if an update fails. Either continue or pause Default is pause.

update_config: 
  parallelism: 2 
  delay: 10s

resources

To configure resource constraints. This replaces the older resource constraint options in Compose files prior to version 3 (cpu_shares, cpu_quota, cpuset, mem_limit, memswap_limit).

resources:
  limits:
    cpus: '1.5'
    memory: 500M
  reservations:
    cpus: '1.0'
    memory: 200M

restart_policy

To configure whether and how to restart containers when they exit.

• condition: One of none, on-failure or any. Default is any.
• delay: How long to wait between restart attempts. Default is 0.
• max_attempts: How many times to attempt to restart a container before giving up. Default is never give up.
• window: How long to wait before deciding if a restart has succeeded. Default is decide immediately.

restart_policy: 
   condition: on-failure 
   delay: 5s 
   max_attempts: 3 
   window: 120s

labels

To specify labels for the service. These labels will be set only on the service, and not on any containers for the service.

version: "3"
services:
  web:
    image: web
    deploy:
      labels:
        com.example.description: "This label will appear on the web service"

To set labels on containers instead, use the labels key outside of deploy:

version: "3"
services:
  web:
    image: web
    labels:
      com.example.description: "This label will appear on all containers for the web service"

“docker stack deploy” command

docker stack deploy command (supported only by compose v3) is used to deploy with docker-stack.yml.

This command does not support the build key supported in Compose files, which builds based on a Dockerfile. You need to use pre-built images with docker stack deploy.

Source: ~ Docker Docs

Disclaimer: Content and image source has been mentioned. Special Credit to concerned folks.