Environment Prerequisites

Development and testing performed on Ubuntu 18.04.2 LTS (Bionic Beaver).

Core Architecture

Docker operates on a client-server model utilizing two primary abstractions:

• Images: Read-only templates containing filesystem layers and application dependencies. Think of these as class definitions in object-oriented programming.
• Containers: Runtime instances of images—encapsulated processes with isolated filesystems, network interfaces, and resource constraints.

Installation Procedures

First, purge legacy Docker packages to prevent conflicts:

sudo apt-get remove docker docker-engine docker.io containerd runc
sudo apt-get update
sudo apt-get install docker.io
sudo systemctl enable --now docker

Image Operations

Discover official repositories:

docker search postgres

Retrieve specific versions:

docker pull redis:7-alpine

Inventory local storage:

docker image ls --format "table {{.Repository}}\t{{.Tag}}\t{{.Size}}"

Persistence operations:

# Export to tar archive
docker save -o ~/backups/webapp-v2.tar myregistry/webapp:v2.1

# Import from archive
docker load < ~/backups/webapp-v2.tar

# Create custom image from running container
docker commit -m "Added SSL certificates" -a "DevOps Team" web-server-01 production/nginx-ssl:v1.0

Remove artifacts:

docker rmi --force sha256:abc123...

Container Management

Initializing containers with resource constraints:

docker run -d \
  --name api-gateway \
  --hostname gateway-node \
  -p 8080:80 \
  -p 8443:443 \
  -v /var/log/nginx:/var/log/nginx \
  -e NODE_ENV=production \
  --restart unless-stopped \
  nginx:stable-alpine

Parameter reference:

• -d: Detached mode (daemon)
• --name: Human-readable identifier
• -p HOST:CONTAINER: Port forwarding rules
• -v HOST:CONTAINER: Bind mount volumes
• -e: Environment variable injection
• --restart: Auto-start policy

Interactive access:

# Preferred method: spawns new bash process
docker exec -u root -it api-gateway /bin/sh

# Alternative (attaches to PID 1, blocks when multiple clients connect):
docker attach api-gateway

Lifecycle control:

docker start api-gateway
docker restart api-gateway
docker stop -t 30 api-gateway  # Grace period before SIGKILL
docker rm -v api-gateway       # Remove container and anonymous volumes