Ruan Bekker's Blog

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Creating a Nodejs Hostname App With Docker Stacks on Swarm

Create a Nodejs Application that responds GET requests with its Hostname.

Our nodejs application will sit beind a HAProxy Load Balancer, we are mounting the docker.sock from the host to the container, so as we scale our web application, our load balancer is aware of the changes, and scales as we scale our web application.

Creating the Application:

Our nodejs application:

app.js
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var http = require('http');
var os = require('os');
http.createServer(function (req, res) {
    res.writeHead(200, {'Content-Type': 'text/html'});
    res.end(`My Hostname: ${os.hostname()}\n`);
}).listen(8080);

Our Dockerfile:

Dockerfile
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FROM node:alpine
ADD app.js /app.js
CMD ["node", "/app.js"]

Build and Push to your registry, or you could use my image on Dockerhub: hub.docker.com/r/rbekker87/node-containername

Build and Push
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$ docker login
$ docker build -t <username>/<repo>:<tag> .
$ docker push  <username>/<repo>:<tag>

Creating the Compose file

Create the compose file that will define our services:

docker-compose.yml
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version: '3'

services:
  node-app:
    image: rbekker87/node-containername
    networks:
      - nodenet
    environment:
      - SERVICE_PORTS=8080
    deploy:
      replicas: 20
      update_config:
        parallelism: 5
        delay: 10s
      restart_policy:
        condition: on-failure
        max_attempts: 3
        window: 120s

  loadbalancer:
    image: dockercloud/haproxy:latest
    depends_on:
      - node-app
    environment:
      - BALANCE=leastconn
    volumes:
      - /var/run/docker.sock:/var/run/docker.sock
    ports:
      - 80:80
    networks:
      - nodenet
    deploy:
      placement:
        constraints: [node.role == manager]

networks:
  nodenet:
    driver: overlay

Create the Stack:

Deploy the Stack by specifying the compose file and name of our stack:

Deploy our Stack
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$ docker stack deploy -c docker-compose.yml node

List the Services in the Stack:

List Services in our Stack
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$ docker stack ls
NAME                SERVICES
node                2

List the Tasks in the Stack:

Tasks in our Stack
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$ docker stack ps node
ID                  NAME                  IMAGE                                 NODE     DESIRED STATE       CURRENT STATE            ERROR               PORTS
l5ryfaedzzaq        node_loadbalancer.1   dockercloud/haproxy:latest            dsm-01   Running             Running 40 minutes ago
c8nrrcvek79h        node_node-app.5       rbekker87/node-containername:latest   dsm-01   Running             Running 40 minutes ago
dqii18b2q5nn        node_node-app.10      rbekker87/node-containername:latest   dsm-01   Running             Running 40 minutes ago
vkpw2rugy0ah        node_node-app.11      rbekker87/node-containername:latest   dsm-01   Running             Running 40 minutes ago
mm88nvnvy5lg        node_node-app.12      rbekker87/node-containername:latest   dsm-01   Running             Running 40 minutes ago
oyx8rfqc1xl2        node_node-app.16      rbekker87/node-containername:latest   dsm-01   Running             Running 41 minutes ago

Test out our Application

Test out the Service:

GET Requests
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$ curl -XGET http://127.0.0.1/
My Hostname: a6e34246e73b

$ curl -XGET http://127.0.0.1/
My Hostname: 5de71278be38

$ curl -XGET http://127.0.0.1/
My Hostname: e0b7316fdd51

Scaling Out:

Scale our Application out to 30 replica’s

Scaling Up
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$ docker service scale node-app=30

Scale our Application down to 10 replica’s

Scaling Down
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$ docker service scale node-app=10

Cleanup

Remove the Stack:

Delete the Stack
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$ docker stack rm node
Removing service node_loadbalancer
Removing service node_node-app
Removing network node_nodenet

Resources: