Docker Basics Cheat Sheet by amicheletti

Different pieces of the app are called “services” For example, a service for storing applic­ation data in a database, a service for the front-end, etc.

Services are just “conta­iners in produc­tion.” A service only runs one image, but it manages for example what ports it should use and how many replicas of the container should run.

To define a service, you'll need an docker­-co­mpo­se.yml file.

For example:
version: "­3"
services:
web:
image: amiche­let­ti/­get­-st­art­ed:­part1
deploy:
replicas: 5
resources:
limits:
cpus: "­0.1­"
memory: 50M
restar­t_p­olicy:
condition: on-failure
ports:
- "­80:­80"
networks:
- webnet
networks:
webnet:

Here you define the image to be loaded, how many replicas, the resource limits and the restart condit­ions.

To run it you must first start: docker swarm init

Then run it giving a name:
docker stack deploy -c docker­-co­mpo­se.yml <ap­p_n­ame>

To see the details of containers running in your service, run:
docker stack ps <ap­p_n­ame>

Now each time you request your app (via browser, for example), the load-b­alancer will help you distri­buting the requests to each replica.

To put it down, docker stack rm <ap­p_n­ame>
This puts down the app, but not the "­one­-no­de" swarm we created. Use:
docker swarm leave --force