1. What is Docker ?
2. What is the difference with virtual machines ?
3. Install and Run Hello world
4. Play with docker
5. Dockerfile
6. Docker Images
7. Docker Containers
8. Tag/Versioning
9. Docker Cheat Sheet
10. Dockerize the Node application
11. Docker Compose
12. What is Docker Swarm ?
13. What is the difference with Kubernetes
14. Create and init the docker swarm cluster
15. Publish our docker image to docker hub repository
16. Docker Swarm visualizer
17. Scaling & Load Balancing
18. Monitor the docker swarm cluster
19. Auto scaling

What is Docker ?

Docker is an open source project to pack, ship and run any application as a lightweight container.

Docker containers are both hardware-agnostic and platform-agnostic. This means they can run anywhere, from your laptop to the largest cloud compute instance and everything in between — and they don’t require you to use a particular language, framework or packaging system. That makes them great building blocks for deploying and scaling web apps, databases, and backend services without depending on a particular stack or provider. — @Docker

Why docker ?

• Rapid application deployment
• Portability across machines
• Version control and component reuse
• Sharing of images/dockerfiles
• Lightweight footprint and minimal overhead
• Simplified maintenance

What is the difference with virtual machines ?

Figure 1.1 | Containers and Virtual Machines | Source: Docker.com

Install and Run Hello world

Pull an image from a registry (Dockerhub)

docker pull hello-world

Run hello-world image

docker run hello-world

Play with docker

Docker Playground

Some terms we will notice when working with docker

Dockerfile: A Dockerfile is a text document that contains all the commands a user could call on the command line to assemble an image. Docker image is created using a Docker file.

Docker Images: An image is a read-only template with instructions for creating a Docker container. Often, an image is based on another image, with some additional customization.

Docker Containers: A container is a runnable instance of an image. You can create, start, stop, move, or delete a container using the Docker API or CLI. In addition, you can connect a container to one or more networks, attach storage to it, or even create a new image based on its current state.

stateDiagram-v2
  Dockerfile --> Image
  Image--> Container

Deploying a Node Application

Creating a Dockerfile

Create a simple Dockerfile in the app root directory as Dockerfile (case sensitive), with no extension.

FROM node:14.17.0-alpine

WORKDIR /app

ADD package*.json ./

RUN npm install
COPY index.js ./
CMD [ "node", "index.js"]

Time to explore .dockerignore. This allows you to exclude files from the context like a .gitignore file will enable you to exclude files from your git repository.

node_modules
npm-debug.log

Building image

docker build -t / .

docker build -t programminghero/explore-docker .

Running a Docker image

docker run -p 80:8080 -d /

docker run -p 80:8080 -d programminghero/explore-docker

-d flag is added to run the container in detached mode, leaving the container running in the background, and the -p flag redirects a public port to a private port inside the container.

http://localhost:8080

Docker Some other commands

List all images that are locally stored with the Docker Engine

docker image ls

Delete an image from the local image store docker image rm <repository-name>:<tag>

docker image rm explore-docker:1.0

Stop a running container through SIGTERM

docker container stop :container_id

Stop a running container through SIGKILL

docker container kill :container_id

Cheat sheet

Tag/Versioning

Build v2 image of our Node Js app

Docker Compose

Docker Compose is a tool for managing multi-container applications. Docker Compose is bundled with Docker Desktop for Windows and Mac. On Linux, it has to be installed separately, check the installation page for details

Docker Compose can:

• Start and stop multiple containers in sequence.
• Connect containers using a virtual network.
• Handle persistence of data using Docker Volumes.
• Set environment variables.
• Build or download container images as required.

Docker Compose uses a YAML definition file to describe the whole application.

Create a file called docker-compose.yml:

version: "3.9"
services:
  postgres:
    image: postgres
    environment:
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: postgres
    ports:
      - '5432:5432'
    volumes:
      - server-db:/var/lib/postgresql/data
  server:
    build:
      context: .
    environment:
      DB_SCHEMA: postgres
      DB_USER: postgres
      DB_PASSWORD: postgres
      DB_HOST: postgres
    depends_on:
      - postgres
    ports:
      - '3000:3000'

volumes:
  server-db:

Start Docker Compose and run the tests. Compose will build the image as needed and map the data volumes:

docker compose run addressbook npm test

We can start the app and use curl to test the endpoint:

docker compose up -d
curl -w "\n" \
       -X PUT \
       -d "firstName=Bobbie&lastName=Draper" \
       localhost:3000/persons

Let's check our newly created guy:

curl -w "\n" localhost:3000/persons/all

Perfect, now that everything works, push all the new code to GitHub:

What is Docker Swarm ?

Docker Swarm is native clustering for Docker. It turns a pool of Docker hosts into a single, virtual host using an API proxy system.

Lets understand what a CLUSTER mean first.

A cluster is a set of tightly coupled computers that function like a single machine. The individual machines, called nodes, communicate with each other over a very fast network, and they’re physically very close together, perhaps in the same cabinet. Usually they have identical or nearly identical hardware and software. All the nodes can handle the same types of request. Sometimes one node takes requests and dispatches them to the others. — Phil Dougherty

Ok so now let’s see what we can accomplish creating a Docker Swarm Cluster:

• Multi-host networking
• Scalling
• Load Balancing
• Security by default
• Cluster management

What is the difference with Kubernetes

Publish our docker image to docker hub repository

docker login
docker image push programminghero/image-name

Create and init the docker swarm cluster

docker swarm init

For deploy our stack we need to run

docker stack deploy -c docker-compose.yml swarmnodeapp

service and node status check:

docker service ls
docker node ls

Scaling & Load Balancing

for scaling

docker service scale swarmnodeapp_nodeapp=50

Docker Swarm visualizer

docker container run -p 8080:8080 -v /var/run/docker.sock:/var/run/docker.sock -d dockersamples/visualizer

Monitor the docker swarm cluster

docker run --name rancher --restart=unless-stopped -p 9000:8080 -d rancher/server