Introduction to Docker
Chapter objectives
- Understand what containerization is
- Discover Docker and its ecosystem
- Differentiate containers from virtual machines
- Understand the Docker architecture
1 - What is Containerization?
The historical problem
Before containers, application deployment posed many challenges:
Développeur : "Ça marche sur ma machine !"
Ops : "Mais pas en production..."
Common causes:
- Different dependency versions
- Variable system configuration
- Missing libraries
- Heterogeneous environments
The solution: containers
A container is a standardized software unit that packages:
- The application code
- Dependencies (libraries, frameworks)
- Configuration
- The runtime environment
┌─────────────────────────────────────────────────┐
│ Conteneur Docker │
├─────────────────────────────────────────────────┤
│ Application + Dépendances + Configuration │
│ ── ─────────────────────────────────────────── │
│ Isolation du système hôte │
└─────────────────────────────────────────────────┘
2 - What is Docker?
Definition
Docker is an open-source platform that lets you:
- Build containerized images
- Distribute these images via registries
- Run containers in isolation
History
| Year | Event |
|---|---|
| 2013 | Docker created by Solomon Hykes (dotCloud) |
| 2014 | Docker 1.0 - Stable version |
| 2017 | Moby Project - Docker becomes open-source |
| 2019 | Docker Desktop for enterprises |
| 2023 | Docker remains the de facto standard |
The Docker ecosystem
┌──────────────────────────────────────────────────────────┐
│ Écosystème Docker │
├──────────────────────────────────────────────────────────┤
│ │
│ ┌─────────────┐ ┌─────────────┐ ┌───────────────── ┐ │
│ │ Docker CLI │ │ Docker │ │ Docker │ │
│ │ │ │ Desktop │ │ Hub │ │
│ └─────────────┘ └─────────────┘ └─────────────────┘ │
│ │
│ ┌─────────────┐ ┌─────────────┐ ┌─────────────────┐ │
│ │ Docker │ │ Docker │ │ Docker │ │
│ │ Compose │ │ Swarm │ │ Registry │ │
│ └─────────────┘ └─────────────┘ └─────────────────┘ │
│ │
└──────────────────────────────────────────────────────────┘
3 - Containers vs Virtual Machines
Compared architecture
Virtual Machine (VM)
┌───────────┐ ┌───────────┐ ┌───────────┐
│ App A │ │ App B │ │ App C │
├───────────┤ ├───────────┤ ├ ───────────┤
│ Bins/Lib │ │ Bins/Lib │ │ Bins/Lib │
├───────────┤ ├───────────┤ ├───────────┤
│ Guest OS │ │ Guest OS │ │ Guest OS │
└───────────┴─┴───────────┴─┴───────────┘
┌─────────────────────────────────────────┐
│ Hyperviseur │
├─────────────────────────────────────────┤
│ Système Hôte │
├─────────────────────────────────────────┤
│ Infrastructure │
└────────────────────────────────────── ───┘
Docker Container
┌───────────┐ ┌───────────┐ ┌───────────┐
│ App A │ │ App B │ │ App C │
├───────────┤ ├───────────┤ ├───────────┤
│ Bins/Lib │ │ Bins/Lib │ │ Bins/Lib │
└───────────┴─┴───────────┴─┴───────────┘
┌─────────────────────────────────────────┐
│ Docker Engine │
├─────────────────────────────────────────┤
│ Système Hôte │
├─────────────────────────────────────────┤
│ Infrastructure │
└─────────────────────────────────────────┘
Comparison table
| Characteristic | VM | Container |
|---|---|---|
| Startup | Minutes | Seconds |
| Size | GB | MB |
| Performance | ~95% | ~99% |
| Isolation | Strong (hardware) | Good (process) |
| OS | Complete | Shared |
| Density | 10-20/server | 100+/server |
When to use what?
Use VMs when:
- Total isolation is required
- Different OSes are needed
- Legacy applications cannot be containerized
Use Docker when:
- Microservices
- Fast CI/CD
- Horizontal scalability
- Development environments
4 - Docker Architecture
The main components
┌──────────────────────────────────────────────────────── ─────┐
│ Client Docker │
│ (docker build, run, pull...) │
└──────────────────────────┬──────────────────────────────────┘
│ REST API
▼
┌─────────────────────────────────────────────────────────────┐
│ Docker Daemon (dockerd) │
├─────────────────────────────────────────────────────────────┤
│ │
│ ┌─────────────┐ ┌─────────────┐ ┌─────────────────────┐ │
│ │ Images │ │ Conteneurs │ │ Réseaux │ │
│ └─────────────┘ └─────────────┘ └─────────────────────┘ │
│ │
│ ┌─────────────┐ ┌─────────────────────────────────────┐ │
│ │ Volumes │ │ containerd │ │
│ └─────────────┘ └─────────────────────────────────────┘ │
│ │
└─────────────────────────────────────────────────────────────┘
Key concepts
1. Docker Daemon (dockerd)
- Service that manages Docker objects
- Listens for API requests
- Communicates with containerd
2. Docker Client (docker)
- Command-line interface
- Sends commands to the daemon
- Can communicate with multiple daemons
3. Docker Registry
- Stores Docker images
- Docker Hub (public)
- Private registries (Harbor, GitLab, etc.)
4. Images
- Read-only templates
- Built from a Dockerfile
- Composed of layers
5. Containers
- Executable instances of images
- Isolated from each other
- Ephemeral by default
5 - Why Docker?
Key benefits
Benefits
1. Portability
- "Build once, run anywhere"
- Same behavior everywhere
2. Efficiency
- Fast startup
- Optimal resource usage
3. Isolation
- No conflicts between applications
- Enhanced security
4. Scalability
- Easy replication
- Orchestration with Kubernetes/Swarm
5. DevOps
- Simplified CI/CD
- Infrastructure as Code
Use cases
| Use case | Description |
|---|---|
| Development | Reproducible environments |
| Testing | Test isolation, parallelization |
| CI/CD | Automated build and deployment |
| Microservices | Modular architecture |
| Cloud Migration | Multi-cloud portability |
6 - Docker Hub
What is Docker Hub?
Docker Hub is Docker's official public registry:
- More than 8 million available images
- Official images maintained by Docker
- Community images
- Free private registries (limited)
Popular images
| Image | Description | Pulls |
|---|---|---|
| nginx | Web server | 1B+ |
| postgres | Database | 500M+ |
| node | JavaScript runtime | 500M+ |
| python | Python interpreter | 500M+ |
| redis | In-memory cache | 500M+ |
Naming conventions
# Format
[registre/]utilisateur/image:tag
# Exemples
nginx # Image officielle, tag latest
nginx:1.25 # Image officielle, tag spécifique
bitnami/nginx # Image communautaire
mon-registre.io/app:v1.0 # Registre privé
7 - First steps
Verify the installation
# Version de Docker
docker --version
# Docker version 24.0.7, build afdd53b
# Informations système
docker info
# Tester avec Hello World
docker run hello-world
Expected output
Hello from Docker!
This message shows that your installation appears to be working correctly.
To generate this message, Docker took the following steps:
1. The Docker client contacted the Docker daemon.
2. The Docker daemon pulled the "hello-world" image from the Docker Hub.
3. The Docker daemon created a new container from that image.
4. The Docker daemon streamed that output to the Docker client.
...
Summary
| Concept | Description |
|---|---|
| Docker | Containerization platform |
| Image | Read-only template |
| Container | Executable instance of an image |
| Registry | Image storage (Docker Hub) |
| Daemon | Service that manages Docker |
Key points
- Docker solves the "it works on my machine" problem
- Containers are lighter and faster than VMs
- Docker Hub provides thousands of ready-to-use images
- The client-server architecture allows great flexibility
Hands-on exercises
- Explain the difference between an image and a container
- Name 3 advantages of containers over VMs
- What is Docker Hub?
- Describe the role of the Docker Daemon