Docker Compose for dev environment - Step-by-Step Execution

Process Flow - Docker Compose for dev environment

Write docker-compose.yml

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Run 'docker-compose up'

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Docker Compose reads config

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Create network and volumes

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Start containers

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Containers run with dev settings

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Develop and test

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Run 'docker-compose down' to stop

Docker Compose reads the config file, sets up containers with dev settings, and runs them for easy development.

Execution Sample

Docker

version: '3.8'
services:
  web:
    build: .
    ports:
      - "3000:3000"
    volumes:
      - .:/app
    environment:
      - NODE_ENV=development

This docker-compose.yml defines a web service that builds from current folder, maps port 3000, mounts current folder for live code updates, and sets NODE_ENV to development.

Process Table

Step	Action	Evaluation	Result
1	Read docker-compose.yml	Parse YAML	Services: web defined with build, ports, volumes, environment
2	Create network	Default network created	Network 'default' ready
3	Create volume	Mount current folder	Volume mount .:/app set for web
4	Build image	Dockerfile in .	Image built for web service
5	Start container	Run container with ports and env	Container 'web' running on port 3000 with NODE_ENV=development
6	Container running	Code changes synced via volume	Live reload possible during development
7	Run 'docker-compose down'	Stop and remove containers	Containers stopped and network removed

💡 Stopped after 'docker-compose down' command to clean up dev environment

Status Tracker

Variable	Start	After Step 4	After Step 5	Final
Network	None	default network created	default network active	removed after down
Volume	None	volume mount set	volume active	removed after down
Container web	None	image built	container running	container stopped and removed

Key Moments - 3 Insights

Why do we mount the current folder as a volume in the web service?

Mounting the current folder allows live code changes to be reflected inside the container immediately, enabling fast development without rebuilding the image. See execution_table step 3 and 6.

What happens when we run 'docker-compose down'?

'docker-compose down' stops running containers and removes the network and volumes created for the dev environment, cleaning up resources. See execution_table step 7.

Why do we set NODE_ENV=development in environment variables?

Setting NODE_ENV=development tells the app inside the container to run in development mode, enabling features like debugging and live reload. See execution_table step 5.

Visual Quiz - 3 Questions

Look at the execution table, at which step is the container actually started?

A Step 3

B Step 4

C Step 5

D Step 6

💡 Hint

Check the 'Action' column for when the container runs with ports and environment.

According to the variable tracker, what is the state of the network after step 5?

A No network created

B Default network active

C Network removed

D Custom network active

💡 Hint

Look at the 'Network' row under 'After Step 5' in variable_tracker.

If we remove the volume mount from the compose file, what changes in the execution?

A Code changes won't reflect live inside container

B Code changes inside container update live

C Container will not start

D Ports will not be mapped

💡 Hint

Refer to key_moments about volume mount and live code updates.

Concept Snapshot

Docker Compose for dev environment:
- Define services in docker-compose.yml
- Use volumes to mount code for live updates
- Map ports to access apps
- Set environment variables for dev mode
- Run 'docker-compose up' to start
- Run 'docker-compose down' to stop and clean

Full Transcript

Docker Compose helps developers run multiple containers easily for development. You write a docker-compose.yml file describing your app's services, ports, volumes, and environment variables. When you run 'docker-compose up', it reads this file, creates a network, mounts your code folder inside the container for live updates, builds the image, and starts the container. This setup lets you develop and test your app quickly. When done, 'docker-compose down' stops containers and cleans up resources. This visual trace showed each step from reading the config to running and stopping containers, tracking network, volume, and container states.