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Docker Basics Cheat Sheet by

Docker Image

docker images
See all available images
docker build -t <na­me>
Create an image with a pretty name (you must define the
Dockerfile
in the folder)
docker tag <na­me> userna­me/­rep­osi­tor­y:tag
This tags an image ready to be sent to a repository
docker push userna­me/­rep­osi­tor­y:tag
Push the image to the remote repository
docker search <ke­ywo­rd>
Search for public reposi­tories
Docker Images are the base for
containers
and are similar to
.iso
files. They can be for example the image of your app and contain everything needed to run the applic­ation.

These images can be local or in reposi­tories (and marked with an tag)

To create images, you must create a
Dockerfile
with some docker commands to specify how that image will be created, for example to setup the enviro­nment and a BaseImage.

Services

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
Docker Swarm is available only for version "­3"
 

Docker Container

docker run <im­age>
Run the image, starting a Container
-d
Run in detached mode (in backgr­ound)
-p 4000:80
Maps the port
80
of the image to the host port
4000
--rm
Removes the container when exited
docker ps
List the running containers (you can check container id)
docker ps -l
List all the containers (you can check container id)
docker stop <co­nta­ine­r_i­d>
Stop the container
When you run an image with you are starting a Container, so container is the runtime instance of an
image
, and consists of the image, an execution enviro­nment and a standart set of instru­ctions.

Swarm

docker swarm init
Initialize a swarm and become
swarm manager
docker swarm join
Join a swarm as
worker
docker swarm leave --force
Leaves the current swarm
With Docker you can increase resource and capacities by creating a
swarm
, which are simply several machines (virtual or physical) running a Docker and joined to a cluster.

Swarms have the
swarm manager
, which can issue docker commands normally, and the
workers
which are only there to provide capacity.
 

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