Dockerizing a node.js app

Before applying the following steps, make sure you have docker installed in you computer/server.

Step 1: Clone repo

git clone https://github.com/eraldoforgoli/node-docker-test.git

Step 2: Build an image of the Dockerfile located in the root of this repo

docker build -t node-docker-test .

the . in the end of the command above represents the path of the Dockerfile, currently . because i am running the docker command in the location of git repository

Step 3: Run an instance of this image

docker run -d -p 8085:8000 node-docker-test

-d stands for detached mode
-p stand for port binding, bind the 8085 port in your local machine/server to port 8000 that docker exposes.

If you open localhost:8085 in your browser, you should see the app running.

Using Services to enable load-balancing

A docker-compose.yml file is a YAML file that defines how Docker containers should behave in production.

version: "3"
services:
  web:
    # replace username/repo:tag with your name and image details
    image: eraldoforgoli/node-docker-test
    deploy:
      replicas: 5
      resources:
        limits:
          cpus: "0.6"
          memory: 200M
      restart_policy:
        condition: on-failure
    ports:
      - "8083:8000"
    networks:
      - webnet
networks:
  webnet:

This docker-compose.yml file tells Docker to do the following:

I have pushed my image in Docker Hub (image cloud based repository), so it can be downloaded by swarm (as specified in the file above)

    image: eraldoforgoli/node-docker-test

Run 5 instances of that image as a service called web, limiting each one to use, at most, 60% of a single core of CPU time and 200mb of memory

 replicas: 5
      resources:
        limits:
          cpus: "0.6"
          memory: 200M

Immediately restart containers if one fails.

      restart_policy:
        condition: on-failure

If you take a look at Dockerfile, you can see that i have EXPOSED port 8000, so i am mapping port 8083 to port 8000. Instruct web’s containers to share port 8000 via a load-balanced network called webnet

    ports:
      - "8083:8000"

Run your new load-balanced app

After adding this file in the root directory, you can run your load balanced app

1. Initialize docker swarm

docker swarm init

2. Run the app

docker stack deploy -c docker-compose.yml node-docker-test-swarm

3. Take a look if your replicas have started

docker service ls

You should see something similar to this:

ID                  NAME                         MODE                REPLICAS            IMAGE                                   PORTS
dmy3gw1s2rgt        node-docker-test-swarm_web   replicated          5/5                 eraldoforgoli/node-docker-test:latest   *:8083->8000/tcp

Check if your containers are up and running

Don't wanste time opening your browser and typing http://localhost:8083, just curl it

curl http://localhost:8083

You should receive a "Hello World!" message.