Docker pro zacatecniky: Od prvniho obrazu po nasazeni do produkce

Docker zmenil zpusob, jakym staviame, dodavame a spoustime software. Misto "na mem pocitaci to funguje" Docker zarucuje, ze vase aplikace bezi vsude stejne - na vasem notebooku, na pocitaci kolegy, v CI/CD a v produkci. V tomto pruvodci pujdeme od nuly az k nasazeni realne aplikace.

Co je Docker?

Docker je platforma, ktera balickuje vasi aplikaci a vsechny jeji zavislosti do standardizovane jednotky zvane kontejner. Kontejner je izolovan, lehky proces, ktery sdili jadro operacniho systemu hostitele, ale ma vlastni souborovy system, sit a prostor procesu.

Kontejnery vs Virtualni stroje

Instalace Dockeru

# macOS
brew install --cask docker

# Ubuntu/Debian
curl -fsSL https://get.docker.com | sh
sudo usermod -aG docker $USER

# Verify installation
docker --version
docker run hello-world

Zakladni koncepty

Obrazy

Obraz je sablona pouze pro cteni s instrukcemi pro vytvoreni kontejneru. Predstavte si ho jako snimek vasi aplikace a jejiho prostredi.

# Pull an image from Docker Hub
docker pull node:20-alpine

# List local images
docker images

# Remove an image
docker rmi node:20-alpine

Kontejnery

Kontejner je bezici instance obrazu. Muzete vytvorit, spustit, zastavit a smazat kontejnery.

# Run a container
docker run -d --name my-app -p 3000:3000 node:20-alpine

# List running containers
docker ps

# List all containers (including stopped)
docker ps -a

# Stop a container
docker stop my-app

# Remove a container
docker rm my-app

# View logs
docker logs my-app

# Execute a command inside a running container
docker exec -it my-app sh

Psani Dockerfile

Dockerfile je textovy soubor s instrukcemi pro sestaveni obrazu. Kazda instrukce vytvori vrstvu.

Zakladni Dockerfile pro Node.js aplikaci

# Use an official Node.js runtime as base image
FROM node:20-alpine

# Set working directory
WORKDIR /app

# Copy package files first (better caching)
COPY package.json package-lock.json ./

# Install dependencies
RUN npm ci --only=production

# Copy application code
COPY . .

# Expose the port the app runs on
EXPOSE 3000

# Command to run the application
CMD ["node", "server.js"]

Sestaveni a spusteni

# Build the image
docker build -t my-node-app .

# Run the container
docker run -d -p 3000:3000 my-node-app

# Visit http://localhost:3000

Vicefazove sestaveni

Vicefazove sestaveni udrzuji vase produkcni obrazy male oddelenim prostredi pro sestaveni od prostredi pro beh.

# Stage 1: Build
FROM node:20-alpine AS builder
WORKDIR /app
COPY package.json package-lock.json ./
RUN npm ci
COPY . .
RUN npm run build

# Stage 2: Production
FROM node:20-alpine AS runner
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
COPY --from=builder /app/package.json ./
EXPOSE 3000
CMD ["node", "dist/server.js"]

Toto vytvori obraz pouze s kompilovanym vystupem a produkcnimi zavislostmi - bez zdrojoveho kodu, bez vyvojovych zavislosti, bez nastroju pro sestaveni.

Priklad vicefazoveho sestaveni pro Next.js

FROM node:20-alpine AS deps
WORKDIR /app
COPY package.json package-lock.json ./
RUN npm ci

FROM node:20-alpine AS builder
WORKDIR /app
COPY --from=deps /app/node_modules ./node_modules
COPY . .
RUN npm run build

FROM node:20-alpine AS runner
WORKDIR /app
ENV NODE_ENV=production
COPY --from=builder /app/public ./public
COPY --from=builder /app/.next/standalone ./
COPY --from=builder /app/.next/static ./.next/static
EXPOSE 3000
CMD ["node", "server.js"]

Svazky: Trvala data

Ve vychozim nastaveni jsou data uvnitr kontejneru ztracena pri jeho odstraneni. Svazky tento problem resi.

# Create a named volume
docker volume create my-data

# Run with a volume
docker run -d -v my-data:/app/data my-app

# Bind mount (map host directory to container)
docker run -d -v $(pwd)/data:/app/data my-app

# List volumes
docker volume ls

Sitove pripojeni

Docker vytvari izolovane site pro komunikaci kontejneru.

# Create a custom network
docker network create my-network

# Run containers on the same network
docker run -d --name api --network my-network my-api
docker run -d --name db --network my-network postgres:16

# Containers can reach each other by name
# From "api" container: postgres://db:5432

Docker Compose

Docker Compose vam umoznuje definovat a spoustet vicekontejerove aplikace s jednim YAML souborem.

docker-compose.yml

services:
  api:
    build: ./api
    ports:
      - "3000:3000"
    environment:
      - DATABASE_URL=postgres://user:pass@db:5432/mydb
    depends_on:
      - db

  db:
    image: postgres:16-alpine
    environment:
      - POSTGRES_USER=user
      - POSTGRES_PASSWORD=pass
      - POSTGRES_DB=mydb
    volumes:
      - pgdata:/var/lib/postgresql/data
    ports:
      - "5432:5432"

  redis:
    image: redis:7-alpine
    ports:
      - "6379:6379"

volumes:
  pgdata:

Prikazy

# Start all services
docker compose up -d

# View logs
docker compose logs -f

# Stop all services
docker compose down

# Rebuild and restart
docker compose up -d --build

# Scale a service
docker compose up -d --scale api=3

.dockerignore

Stejne jako .gitignore tento soubor zabranuje kopirovani nepotrebnych souboru do obrazu.

node_modules
.git
.env
*.md
.next
dist
coverage

Osvedcene postupy pro produkci

1. Pouzivejte male zakladni obrazy

# Bad: 1GB+
FROM node:20

# Good: ~180MB
FROM node:20-alpine

2. Nespoustejte jako Root

FROM node:20-alpine
RUN addgroup -S app && adduser -S app -G app
USER app
WORKDIR /home/app
COPY --chown=app:app . .

3. Pouzivejte specificke tagy obrazu

# Bad: can change unexpectedly
FROM node:latest

# Good: pinned version
FROM node:20.11-alpine3.19

4. Vyuzijte cache sestaveni

Seradte instrukce Dockerfile od nejmene po nejvice casto menenych:

FROM node:20-alpine
WORKDIR /app

# These change rarely - cached
COPY package.json package-lock.json ./
RUN npm ci --only=production

# This changes often - not cached
COPY . .

5. Kontroly zdravi

HEALTHCHECK --interval=30s --timeout=3s --retries=3 \
  CMD wget -qO- http://localhost:3000/health || exit 1

6. Pouzivejte promenne prostredi

ENV NODE_ENV=production
ENV PORT=3000

Tahak beznych prikazu Dockeru

# Images
docker build -t name:tag .        # Build image
docker images                      # List images
docker rmi image_name              # Remove image
docker image prune                 # Remove unused images

# Containers
docker run -d -p 3000:3000 image   # Run detached
docker ps                          # List running
docker stop container_name         # Stop
docker rm container_name           # Remove
docker logs -f container_name      # Follow logs
docker exec -it container sh       # Shell into container

# Compose
docker compose up -d               # Start services
docker compose down                # Stop services
docker compose logs -f             # Follow all logs
docker compose ps                  # List services

# Cleanup
docker system prune -a             # Remove everything unused

Od Dockeru ke Kubernetes

Docker spravuje jednotlive kontejnery. Kdyz potrebujete orchestrovat stovky kontejneru na vice serverech, potrebujete Kubernetes. Docker a Kubernetes se doplnuji:

1. Docker: stavi a spousti kontejnery
2. Kubernetes: orchestruje kontejnery ve velkem meritku (planovani, skalovani, samooprava)

Pokud vas zajima dalsi krok, podivejte se na muj clanek o Uvodu do Kubernetes.

Zaver

Docker je zakladni dovednost pro moderni vyvojare. Eliminuje nesrovnalosti prostredi, zjednodusuje nasazeni a je zakladem pro orchestraci kontejneru s Kubernetes. Zacnete s jednoduchym Dockerfile, prejdete na Docker Compose pro vicesluzbove aplikace a prijmete vicefazove sestaveni a osvedcene postupy zabezpeceni jak budete rust.

Nejlepsi zpusob, jak se naucit Docker, je kontejnerizovat projekt, na kterem uz pracujete. Zacnete dnes.