docker

Architecture

• Client: docker CLI
• Daemon: dockerd (does the work)
• Registry: where images live

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Images (Build-time)

• Image: immutable filesystem + metadata
• Dockerfile: build recipe
• Layer: cached filesystem diff
• Tag: human label (nginx:1.25)
• Digest: real identity (hash)
• Base image: starting point

Core commands:

docker build -t app . 
docker pull image 
docker push image 
docker images

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Containers (Run-time)

• Container: running instance of image
• PID 1: main process
• Lifecycle: create → start → stop → rm

Core commands:

docker run 
docker ps 
docker stop 
docker exec 
docker logs 
docker rm

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Storage

• Volume: Docker-managed (preferred)
• Bind mount: host path
• tmpfs: memory only

Core commands:

docker volume create

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Networking

• Bridge (default)
• Host
• Overlay
• Port mapping: HOST:CONTAINER
• DNS: container name resolution

Core commands:

docker network create

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Inspection & Ops

Core commands:

docker inspect 
docker stats 
docker system df 
docker prune

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Installing Docker

1. Set up Docker’s apt repository.

# Add Docker's official GPG key:
sudo apt update
sudo apt install ca-certificates curl
sudo install -m 0755 -d /etc/apt/keyrings
sudo curl -fsSL https://download.docker.com/linux/ubuntu/gpg -o /etc/apt/keyrings/docker.asc
sudo chmod a+r /etc/apt/keyrings/docker.asc
    
# Add the repository to Apt sources:
sudo tee /etc/apt/sources.list.d/docker.sources <<EOF
Types: deb
URIs: https://download.docker.com/linux/ubuntu
Suites: $(. /etc/os-release && echo "${UBUNTU_CODENAME:-$VERSION_CODENAME}")
Components: stable
Signed-By: /etc/apt/keyrings/docker.asc
EOF
sudo apt update

2. Install the Docker packages.

sudo apt install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

See Also

• Docker vs VM
• docker compose