<h1 style='font-size:26px;color:#6aa84f;'>docker: link a node.js container with a mongodb container with legacylinking</h1>

To use docker in an enviroment where you have to seperate database from webserver and webserver from contentserver you can use 2 methods in docker.
Today we want to have a  look on Legacy Linking. Like the name describes is this the simplest method to link containers, wich can be marked as deprecated in the future.

This methods simply runs the dependend containers with the --link attribute

 

Prerequisits

We need some things installed on the local machine.

• docker installed
• git installed 
• a dockerhub account (visit http://hub.docker.com)

 

Install node.js pet-app

We want to use a little pet app with node.js. It starts an express server and connects to a mongodb server "my-mongodb". The app simply lists some docs pics and some describing texts

Clone the app repository in your projectroot

$ git clone https://github.com/pboethig/dockerlessons.git

$ cd dockerlessons/legacyLinking

 

Inspect the dockerfile

In the projectroot you find a "node.dockerfile" this is the dockerfile for our node webserver with the node.js app in it

This is the content

FROM node:latest

MAINTAINER Peter Böthig

ENV NODE_ENV=production
ENV PORT=3000

COPY . /var/www
WORKDIR /var/www

RUN npm install

EXPOSE $PORT

ENTRYPOINT ["npm", "start"]

To explain that

• Line 1 load a node baseimage
• Line 2 define a maintainer (your username in thinat case)
• Line 3 & 4 define enviromentvariables, to switch from dev to prod
• Line 5 copy our sourcecode to the container in "var/www"
• LINE 6 define a workingdirectory
• Line 7 run npm install
• Line 8 Expose the default webserverport (prod/live)
• Line 9 start the express webserver

In the follwing we use <your_docker_username>. Please make sure you have an account

 

Create our image from the Dockerfile

Now, that we have created our Dockerfile we can create our first image from it.

Open a terminal in the folder where your Dockerfile lives

docker build -f node.dockerfile -t <your_docker_username>/node-pet-app .

Don't forget the last point at the end of the line, otherwhis nothing will be found to image. The first load could take some seconds.

You can see you new image with

docker images

Create your mongo-database-container

Our pet app needs a mongodatabase where the pet data live. We simply use an image from the docker hiu

Pull the image and create a named container

docker run -d --name my-mongodb mongo

This will download the mongo-image and create a container "my-mongodb". The name "my-mongodb" is important, because it's  mapped to the configured databasename "mongodb" in our config/config.production.js of our pet app.

 

Create our node-app container and link it to the databasecontainer

Now that we have created our node.js app image and have our database up and running, we want to create our app server and link it to our pet database.

Run and link the containers

docker run -d -p 8080:3000 --link mymongodb:mongodb --name nodeapp <your_docker_username>/node-pet-app

To explain that:

• -d -> starts container detached, so the console can be used
  
• -p 8080:3000 -> maps the hostport 8080 on the containerport 3000
  
• --link my-mongodb:mongodb -> creates a link "mongodb" from to the container "my-mongodb". So "mongodb" can be found in the network
  
• --name nodeapp <your_docker_username>/node-pet-app -> creates the container "nodeapp" from your app image

Now you can reach your app under http://localhost:8080

This is really great. But you don't see any pets. Thats because you dont have any data in it

Populate database with testdatas

docker exec nodeapp node dbSeeder.js

This will execute "node dbSeeder.js" inside your new container "nodeapp"

That's it. Really awesome stuff. Now your can surf to your new app and see your pets
http://localhost:8080