Week 6 – Docker & Containers: Daily Practice Tasks - snir1551/DevOps-Linux GitHub Wiki

Task 1 – Introduction to Docker CLI

Run Your First Container

docker run hello-world

List Containers and Images
- List running containers:
```
docker ps
```
- List all containers (including stopped)
```
docker ps -a
```
- List downloaded images
```
docker images
```

Stop and Remove Containers
- Stop a running container:
```
docker stop <container_id>
```
- Remove a stopped container:
```
docker rm <container_id>
```
- Remove all stopped containers:
```
docker container prune
```

Remove Docker Images
- Remove a specific image:
```
docker rmi <image_id>
```
- Remove all unused images:
```
docker image prune
```

Task 2 – Working with Docker Images

Pull the nginx Image

docker pull nginx

Run the Web Server

docker run -d -p 8080:80 --name my-nginx nginx

Explanation:

-d: Run in detached mode (in the background)
-p 8080:80: Map port 8080 on your machine (host) to port 80 inside the container (where nginx listens)
--name my-nginx: Assigns a name to the container

Verify the Web Server is Running

curl http://localhost:8080

Use a Lightweight Image

docker pull nginx:alpine
docker run -d -p 8081:80 --name my-nginx-alpine nginx:alpine

Now verify it via:

curl http://localhost:8081

Compare Image Sizes

docker image ls

The alpine version is significantly smaller and ideal for production environments

Cleanup

docker stop my-nginx my-nginx-alpine
docker rm my-nginx my-nginx-alpine

docker rmi nginx nginx:alpine

Task 3 – Dockerfile Basics

Build from Dockerfile

index.js:

import express from 'express';
import dotenv from 'dotenv';

app.get('/', (req, res) => {
  res.send('Hello from Docker\n');
});

app.listen(port, () => {
  console.log(`App is running at http://localhost:${port}`);
});

Dockerfile:

FROM node:18-alpine

WORKDIR /app

COPY package*.json ./

RUN apk add --no-cache curl && rm -rf /var/cache/apk/*

RUN npm install

COPY . .

EXPOSE 3000

HEALTHCHECK --interval=30s --timeout=5s --start-period=5s --retries=3 CMD curl -f http://localhost:3000/ || exit 1

CMD ["npm", "start"]

docker build -t hello-from-dockerfile .

Run Your Custom App

docker run -d -p 3000:3000 --name docker_project hello-from-dockerfile

curl http://localhost:3000

Explore Inside Container

docker exec -it docker_project bash
ls -la
exit
docker image ls

Use .dockerignore to Optimize Image Size

before .dockerignore:

after .dockerignore:

Task 4 – Custom Networking and Multi-container Setup

Build App

update index.js:

import express from 'express';
import dotenv from 'dotenv';
import mongoose from 'mongoose';

const host = process.env.MONGO_HOST;
const username = process.env.MONGO_INITDB_ROOT_USERNAME;
const password = process.env.MONGO_INITDB_ROOT_PASSWORD;
const uri = `mongodb://${username}:${password}@${host}:27017/?authSource=admin`;

mongoose.connect(uri)
 .then(() => console.log('Connected to MongoDB via Mongoose'))
 .catch(err => console.error('Connection failed:', err));

app.get('/', (req, res) => {
  res.send('Hello from Docker + Mongoose\n');
});

app.listen(port, () => {
  console.log(`App is running at http://localhost:${port}`);
});

docker build -t docker-webapp .

Create Custom Network

docker network create mynet

docker network ls

Run MongoDB in the Network

docker run -d --name mongodb --network mynet -e MONGO_USERNAME=admin -e MONGO_PASSWORD=1234 mongo

Access MongoDB CLI

docker exec -it mongodb mongosh -u admin -p 1234 --authenticationDatabase admin
use admin
db.system.users.find().pretty()

Run Your Web App in the Network

docker run -d --name webapp --network mynet --env-file .env -p 3000:3000 docker-webapp

docker network inspect mynet

docker logs webapp

Network Diagnostics

docker exec -it webapp bash
apt update && apt install -y iputils-ping
ping mongodb

Task 5 – Docker Compose Intro

Compose Up

docker-compose.yml:

version: '3.8'

services:
  mongodb:
    image: mongo:8.0.10
    container_name: mongodb
    restart: always
    env_file: 
      - .env
    environment:
    MONGO_INITDB_ROOT_USERNAME: ${MONGO_INITDB_ROOT_USERNAME}
    MONGO_INITDB_ROOT_PASSWORD: ${MONGO_INITDB_ROOT_PASSWORD}
    volumes:
      - mongo-data:/data/db
    networks:
      - mynet

  webapp:
    build:
      context: .
    dockerfile: Dockerfile
    image: myapp:1.0.0
    container_name: webapp
    restart: always
    env_file:
      - .env
    environment:
      PORT: ${PORT}
      MONGO_HOST: mongodb
    ports:
      - "3000:3000"
    depends_on:
      - mongodb
    networks:
      - mynet

volumes:
  mongo-data:

networks:
  mynet:
    driver: bridge

docker-compose up -d --build

Check Everything

docker images
docker ps
docker volume ls

curl http://localhost:3000
docker network ls

docker network inspect 16eebe505976

Test Inter-Container Communication

docker exec -it webapp bash
apt update && apt install -y iputils-ping
ping mongodb
CTRL + C
exit

docker logs webapp

Task 6 – Monitoring & Logging Basics

Logs and Inspection

docker logs webapp

docker inspect webapp | grep -A 20 "Health"

Task 7 – Advanced Docker Features

Tag and Push to DockerHub

docker tag myapp:1.0.0 your_dockerhub_username/myapp:1.0.0

docker push your_dockerhub_username/myapp:1.0.0

2 created action

https://github.com/snir1551/DevOps-Linux/blob/main/.github/workflows/docker.yml

The final solution:

https://github.com/snir1551/DevOps-Linux/tree/main/week6_practice