Docker_NodeJs_App

What is Docker?

• It is an open source platform for containerisation
• Docker enables you to separate your infrastructure so you can deliver your software quickly

Why should we use Docker?

• Because it doesn’t make a difference what OS you are using - Increasing its portability and ease of use of the user
• Large library of images to build containers from
• Docker is fast as it only contains the files require to run the app rather than a full on VM
• Provides consistent delivery of your applications and can be scaled up very well

What is container?

• Process of spinning up virtual environments within containers.
• You can pull any container, change the container re tag it and make changes. You can then repush that new container

Benefits of containers

• Creating a vm to test out all operating systems, test installation of software

What is the difference between VMs and Docker

• Docker is lightweight compared to VMs… but how? Docker shares the resources of an OS rather than creating a entire virtual environment.

Microservices

Microservices – Also known as the microservice architecture is an architecture style that structures an application as a collection of services that are: Highly maintainable and testable

• loosely coupled
• Independently deployable
• Organized around business capability’s
• Owned by a small team

Cons

• Results in more complex systems than monolithic architecture - This is unnecessary for small companies

Microservices Docker Nodejs App and db task

App Docker file

# select base image to build our own customised node app microservice

FROM node:alpine

# working directory inside the container

WORKDIR /usr/src/app

# copy dependencies

COPY package*.json ./

# Install npm

RUN npm install

# copy everything from current location to default location inside the container

COPY . .

# define the port

EXPOSE 3000

# start the app with CMD

CMD ["node","app.js"]

docker-compose file

version: '3'

services:
  db:
    image: mongo
    restart: always
    ports: [27017:27017]

  web:
    build: ./app
    restart: always
    ports: [3000:3000]
    environment:
      - DB_HOST=mongodb://db:27017/posts
    depends_on:
      - db

This compose file creates two containers - 1 for the db and 1 for the app

The image used for the db is the base mongo image whereas with the web, the Dockerfile in the app folder is to be used.

We then state which ports need to be allowed for the app/db to be run on.

Environment variables can also be set within this file also.

Since a link has been made between the two services using the depends_on clause, you can refer to the mongodb database by using mongodb://db:27017/posts. Usually we use localhost but in this situation we want to refer to the internal network created by docker.