Some useful Docker stuff

Some common commands necessary to build and run own docker image in a container:

Sample of creating docker image with NodeJs application running in it

1. Create super tiny server app in any local filesystem folder. Name it as app.js.
   

   const http = require('http');
   
   const hostname = '0.0.0.0';
   const port = 3009;
   
   const server = http.createServer((req, res) => {
     res.statusCode = 200;
     res.setHeader('Content-Type', 'text/plain');
     res.end('Hello World');
   });
   
   server.listen(port, hostname, () => {
     console.log(`Server running at //${hostname}:${port}/`);
   });

   Note: it is important here to specify hostname as ‘0.0.0.0’ which tells server to listen on all hosts, which will further allow us to connect to it from local mashine. If you would specify i.e. 127.0.0.1 which basically means localhost or loopback, it will listen only to request from internal docker OS (ubuntu in our case).
2. Create a Dockerfile in the same folder.
   

   FROM ubuntu:latest
   
   RUN apt-get update
   RUN apt-get install -y nodejs
   RUN apt-get install -y npm
   
   RUN mkdir -p /usr/src/myapp
   COPY . /usr/src/myapp
   WORKDIR /usr/src/myapp
   
   RUN npm install
   
   EXPOSE 3009
   
   CMD node ./app.js

   Here we have:
   • FROM ubuntu:latest – tells docker to pull latest version of Ubuntu OS from docker hub (//hub.docker.com)
   • RUN apt-get update – refreshing ubuntu apt-get database
   • RUN apt-get install -y nodejs – installing NodeJs
   • RUN apt-get install -y npm – installing Node package manager
   • RUN mkdir -p /usr/src/myapp – creating directory for our new app
   • COPY . /usr/src/myapp – copy all contents (in our particular case just app.js is relevant) from local current folder to the one we dedicated on ubuntu
   • WORKDIR /usr/src/myapp – tell docker to use this directory as current working one
   • RUN npm install – build NodeJs application
   • EXPOSE 3009 – make port 3009 accessible from outside
   • CMD node ./app.js – instruction to run main app file of our application when container is started. The difference between RUN and CMD instructions is, that the first one is executed on image build and the second one on container start.
     
     Note: installing node and npm via apt-get could be skipped here if we choose to build our own docker image from the one which already has embedded needed software. It basically means we can build new image on any other previously made by us or by others.
3. Build docker image

   docker build -t my-node-app .

4. Run docker image

   docker run  –name my-node-app-container -p 3009:3009 my-node-app

Here we go. We should be able to access new app from local machine via port 3009 on localhost: //localhost:3009. 

Hello World! 🙂