DevOps Classroom notes 08/Jun/2026

Docker compose

• This lets you bring up multiple containers with simple command

docker compose up -d
docker compose down 
# bring down and remove volumes
docker compose down -v

• To use docker compose we need to create an yaml file with name docker-compose.yml
• YAML file is used to represent data in the form of key value pairs
• Each key value pair has the following syntax

key: <value>

• Values can come in many forms
• Simple forms
  • Text
  • Number
  • boolean
• Text

name: QT
name: 'QT'
name: "QT"

• Multi line text

recommendation_letter: |
    Aarav has shown exceptional coding skills.
    He always submits assignments before the deadline.
    He is highly recommended for the internship.

recommendation_letter: >
    Aarav has shown exceptional coding skills.
    He always submits assignments before the deadline.
    He is highly recommended for the internship.

• Number

age: 15
price: 10.99

• boolean:

online: True
online: yes
extraprice: no
extraprice: False

• list/array

colors: ["Red", "Blue"]

colors:
- Red
- Blue

colors:
  - Red
  - Blue

• object/dictionary/map

address:
  flatno: 601-A
  building: nilgiri
  city: Hyderabad
  pincode: 500016

• YAML is used to represent data which is easier to understand to both humans and applications
• When an yaml is meant for application, application defines the structure

This is my yaml schema

• This is my yaml schema to document your favorite movie

title: <text> | movie name | required
release_year: <number> | required
witness_date: <text> | when you watched the movie for first time | required
repeats: <number> | how many time you watched this movie | required
last_watch_date: <text> | when did you watch for the last time | optional

• Example

title: Avengers Infinity War
release_year: 2018
witness_date: 'April 27, 2018'
repeats:  100

• Example

title: Avengers Infinity War
release_year: 2018
witness_date: 'April 27, 2018'
repeats:  100
last_watch_date: 'May 27, 2026'

Docker compose yaml

• reference

Lets write a docker compose file

Case 1

• I want to create an nginx container
• equivalent command

docker run -d -p 19000:80 --name web1 nginx

• Create a file docker-compose.yml with the following

---
services:
  web:
   image: 'nginx:1.31'
   ports:
     - "19000:80"

• Now cd in the folder where you have this compose file

docker compose up -d

• Now access your application on http://localhost:19000/
• To bring them down

docker compose down

Case 2

• I want an nginx container and a mysql contianer
• Mysql and nginx should be in same network
• mysql container requires a volume and it has some enivronment variabls to be passed

# Create network
docker network create app-network

# Create persistent volume for MySQL
docker volume create mysql-data

# Start MySQL container
docker run -d \
  --name mysql \
  --network app-network \
  -v mysql-data:/var/lib/mysql \
  -e MYSQL_ROOT_PASSWORD=rootpassword \
  -e MYSQL_DATABASE=myappdb \
  -e MYSQL_USER=myuser \
  -e MYSQL_PASSWORD=mypassword \
  mysql:8.4

# Start Nginx container
docker run -d \
  --name nginx \
  --network app-network \
  -p 18880:80 \
  nginx:latest

# Verify
docker ps

# Inspect network
docker network inspect app-network

Case 3

• Till now we are using images from docker hub what if we have a docker file
• This means before bringing up the contaienrs it needs to build images.
• To be discussed tomorow