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All technological notes.

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Project: Docker Compose with Multiple local containers

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• Project: Docker Compose with Multiple local containers
  • Goal
  • Web App
    • Node JS app
    • Dockerfile
  • Docker Compose
    • Yaml File
    • Start Docker compose

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Command	Description
docker compose up	Create and start containers
docker compose up -d	Detached mode: Run containers in the background
docker compose up --build	Build images before starting containers
docker compose down	Stop and remove containers, networks

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Goal

• Count number of visit

  • node app + redis

• solution 1:

  • node app and redis in one container
  • problem:
    • when traffic increases, more container need to be introduced to respond to incoming requests. Some values in redis of different container cannot be sync.

• Solution 2:

  • node app in container; redis in one container
  • when scale up, only the node app container needs to be scaled up. The only one container for redis keep the consisitency.

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Web App

Node JS app

• package.json

{
  "dependencies": {
    "express": "*",
    "redis": "2.8.0"
  },
  "scripts": {
    "start": "node index.js"
  }
}

• index.js

const express = require("express");
const redis = require("redis");

const app = express();
// specify the redis container by it name defined in the docker compose file
const client = redis.createClient({
  host: "redis-server",
  port: 6379, // default port for redis
});

client.set("visits", 0);

app.get("/", (req, res) => {
  client.get("visits", (err, visits) => {
    res.send("Number of visits is " + visits);
    client.set("visits", parseInt(visits) + 1);
  });
});

app.listen(8081, () => {
  console.log("Listening on port 8081");
});

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Dockerfile

• Dockerfile

# base image
FROM node:alpine

# install dependencies
WORKDIR '/app'

COPY package.json .
RUN npm install

COPY . .

# startup commands
CMD ["npm", "start"]

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Docker Compose

Yaml File

• docker-compose.yml

services:
  redis-server:
    image: "redis"
  node-app:
    build: .
    ports:
      - "8081:8081"

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Start Docker compose

docker compose up
docker compose up -d
docker ps

docker compose down
docker ps

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