As in my previous article, I wrote steps for Docker installation and had a healthy discussion about sudo docker vs just docker. (Here I will write commands that start with docker)

What is the Problem?

Imagine you're working on multiple projects:

• Project 1 needs Node.js version 18.x

• Project 2 needs Node.js v20.x

• Some projects need an older MongoDB version

• Others need the current MongoDB version

What would you do? Install and reinstall versions one by one? This approach is difficult because:

• Every version must be configured accordingly

• Installed versions may conflict with each other

• Managing dependencies becomes a nightmare

What is the Solution?

Virtual machines are one solution, but they're resource-heavy and difficult to manage. You'd need to:

• Spin VMs on and off

• Connect services between different VMs

• Connect VM services with your local machine

Docker changes everything! It can:

• Spin environments up and down in seconds

• Run services instantly

• Connect all services with your local machine out of the box

• Simply map ports to connect services

  

Docker Terminology

1. Docker Image: A blueprint or template containing the code and dependencies needed to run a service. Think of it as a program stored on your machine, not executing but ready to run.

2. Docker Container: A running instance of a Docker image. It's like a process - your program in execution. When you run a container, Docker creates a unique instance with its own environment.

Each container is unique by default through a container ID, even if you don't pass any variables. You can also pass environment variables to customize containers.

Prerequisites: If you don't have Docker installed, refer to this article: Docker installation guide

Docker Commands for Images

1. Download an Image

Browse Docker Hub to find the image you need:

docker pull <image_name>

Examples:

docker pull postgres          # Latest postgres version
docker pull postgres:16       # Specific postgres version
docker pull node:18-alpine    # Node.js 18 with Alpine Linux

2. List All Images

docker images

3. Remove an Image

docker rmi <image_id_or_name>

Example:

docker rmi postgres:16

Docker Commands for Containers

1. Run a Container

docker run <image_name>

Example:

docker run hello-world

2. Run with Interactive Terminal

docker run -it <image_name> /bin/bash

Example:

docker run -it ubuntu /bin/bash

3. Run in Background with Port Mapping

docker run -d --name <custom_container_name> -p <host_port>:<container_port> <image_name>

Examples:

# Redis server
docker run -d --name my-redis -p 6379:6379 redis

# PostgreSQL database
docker run -d --name my-postgres -p 5432:5432 -e POSTGRES_PASSWORD=mypassword postgres

# MongoDB
docker run -d --name my-mongo -p 27017:27017 mongo

Best Practice: Map host and container ports to the same number (e.g., 6379:6379) for consistency.

4. List Running Containers

docker ps

5. List All Containers (including stopped)

docker ps -a

6. Container Lifecycle Management

# Stop a running container
docker stop <container_id_or_name>

# Start a stopped container
docker start <container_id_or_name>

# Restart a container
docker restart <container_id_or_name>

# Remove a container (must be stopped first)
docker rm <container_id_or_name>

# Force remove a running container
docker rm -f <container_id_or_name>

Interacting with Active Containers

1. Execute Commands Inside a Container

docker exec -it <container_id_or_name> bash

Examples:

# Access PostgreSQL CLI
docker exec -it my-postgres psql -U postgres

# Access Redis CLI
docker exec -it my-redis redis-cli

# General bash access
docker exec -it my-container bash

2. View Container Logs

docker logs <container_id_or_name>

# Follow logs in real-time
docker logs -f <container_id_or_name>

# Show last 100 lines
docker logs --tail 100 <container_id_or_name>

3. Copy Files Between Container and Host

# Copy from container to host
docker cp <container_id>:/path/to/file ./local/path

# Copy from host to container
docker cp ./local/file <container_id>:/path/to/destination

Practical Examples

Setting up a Development Environment

# PostgreSQL database
docker run -d --name dev-postgres -p 5432:5432 -e POSTGRES_PASSWORD=dev123 postgres:16

# Redis cache
docker run -d --name dev-redis -p 6379:6379 redis:7-alpine

# MongoDB database
docker run -d --name dev-mongo -p 27017:27017 mongo:7

Cleanup Commands

# Stop all running containers
docker stop $(docker ps -q)

# Remove all stopped containers
docker rm $(docker ps -aq)

# Remove unused images
docker image prune

# Remove everything (use with caution!)
docker system prune -a

Next Steps

Now that you understand basic Docker commands, you're ready to:

• Set up development environments quickly

• Test different software versions without conflicts

• Share consistent environments with your team