1 
2Docker a schimbat modul in care construim, livram si rulam software. In loc de "functioneaza pe masina mea", Docker garanteaza ca aplicatia ta ruleaza la fel peste tot - pe laptopul tau, pe masina unui coleg, in CI/CD si in productie. In acest ghid, vom merge de la zero la deploy-ul unei aplicatii reale.
3 
4## Ce este Docker?
5 
6Docker este o platforma care impacheteaza aplicatia ta si toate dependentele sale intr-o unitate standardizata numita **container**. Un container este un proces izolat si usor care partajeaza kernel-ul OS-ului gazda, dar are propriul sistem de fisiere, retea si spatiu de procese.
7 
8```mermaid
9graph TD
10    subgraph "Traditional Deployment"
11        A1[App 1] --> OS1[Guest OS]
12        A2[App 2] --> OS2[Guest OS]
13        OS1 --> HV[Hypervisor]
14        OS2 --> HV
15        HV --> HW1[Hardware]
16    end
17 
18    subgraph "Docker Deployment"
19        B1[App 1] --> D1[Container]
20        B2[App 2] --> D2[Container]
21        D1 --> DE[Docker Engine]
22        D2 --> DE
23        DE --> HW2[Hardware]
24    end
25```
26 
27### Containere vs Masini Virtuale
28 
29| Aspect | Containere | Masini Virtuale |
30|--------|-----------|-----------------|
31| **Pornire** | Secunde | Minute |
32| **Dimensiune** | MB | GB |
33| **SO** | Partajeaza kernel-ul gazdei | SO oaspete complet |
34| **Izolare** | Nivel de proces | Nivel hardware |
35| **Performanta** | Aproape nativa | Overhead de la hypervisor |
36| **Densitate** | Sute per gazda | Zeci per gazda |
37 
38## Instalarea Docker
39 
40```bash
41# macOS
42brew install --cask docker
43 
44# Ubuntu/Debian
45curl -fsSL https://get.docker.com | sh
46sudo usermod -aG docker $USER
47 
48# Verify installation
49docker --version
50docker run hello-world
51```
52 
53## Concepte Fundamentale
54 
55### Imagini
56 
57O imagine este un sablon doar pentru citire cu instructiuni pentru crearea unui container. Gandeste-te la ea ca la un instantaneu al aplicatiei si al mediului sau.
58 
59```bash
60# Pull an image from Docker Hub
61docker pull node:20-alpine
62 
63# List local images
64docker images
65 
66# Remove an image
67docker rmi node:20-alpine
68```
69 
70### Containere
71 
72Un container este o instanta in executie a unei imagini. Poti crea, porni, opri si sterge containere.
73 
74```bash
75# Run a container
76docker run -d --name my-app -p 3000:3000 node:20-alpine
77 
78# List running containers
79docker ps
80 
81# List all containers (including stopped)
82docker ps -a
83 
84# Stop a container
85docker stop my-app
86 
87# Remove a container
88docker rm my-app
89 
90# View logs
91docker logs my-app
92 
93# Execute a command inside a running container
94docker exec -it my-app sh
95```
96 
97## Scrierea unui Dockerfile
98 
99Un Dockerfile este un fisier text cu instructiuni pentru construirea unei imagini. Fiecare instructiune creeaza un strat.
100 
101### Dockerfile de Baza pentru o Aplicatie Node.js
102 
103```dockerfile
104# Use an official Node.js runtime as base image
105FROM node:20-alpine
106 
107# Set working directory
108WORKDIR /app
109 
110# Copy package files first (better caching)
111COPY package.json package-lock.json ./
112 
113# Install dependencies
114RUN npm ci --only=production
115 
116# Copy application code
117COPY . .
118 
119# Expose the port the app runs on
120EXPOSE 3000
121 
122# Command to run the application
123CMD ["node", "server.js"]
124```
125 
126### Construire si Rulare
127 
128```bash
129# Build the image
130docker build -t my-node-app .
131 
132# Run the container
133docker run -d -p 3000:3000 my-node-app
134 
135# Visit http://localhost:3000
136```
137 
138## Build-uri Multi-Stage
139 
140Build-urile multi-stage mentin imaginile de productie mici separand mediul de build de runtime.
141 
142```dockerfile
143# Stage 1: Build
144FROM node:20-alpine AS builder
145WORKDIR /app
146COPY package.json package-lock.json ./
147RUN npm ci
148COPY . .
149RUN npm run build
150 
151# Stage 2: Production
152FROM node:20-alpine AS runner
153WORKDIR /app
154COPY --from=builder /app/dist ./dist
155COPY --from=builder /app/node_modules ./node_modules
156COPY --from=builder /app/package.json ./
157EXPOSE 3000
158CMD ["node", "dist/server.js"]
159```
160 
161Aceasta produce o imagine doar cu iesirea compilata si dependentele de productie - fara cod sursa, fara dependente de dezvoltare, fara instrumente de build.
162 
163### Exemplu Multi-Stage pentru Next.js
164 
165```dockerfile
166FROM node:20-alpine AS deps
167WORKDIR /app
168COPY package.json package-lock.json ./
169RUN npm ci
170 
171FROM node:20-alpine AS builder
172WORKDIR /app
173COPY --from=deps /app/node_modules ./node_modules
174COPY . .
175RUN npm run build
176 
177FROM node:20-alpine AS runner
178WORKDIR /app
179ENV NODE_ENV=production
180COPY --from=builder /app/public ./public
181COPY --from=builder /app/.next/standalone ./
182COPY --from=builder /app/.next/static ./.next/static
183EXPOSE 3000
184CMD ["node", "server.js"]
185```
186 
187## Volume: Date Persistente
188 
189In mod implicit, datele din interiorul unui container se pierd cand containerul este eliminat. Volumele rezolva aceasta problema.
190 
191```bash
192# Create a named volume
193docker volume create my-data
194 
195# Run with a volume
196docker run -d -v my-data:/app/data my-app
197 
198# Bind mount (map host directory to container)
199docker run -d -v $(pwd)/data:/app/data my-app
200 
201# List volumes
202docker volume ls
203```
204 
205## Retea
206 
207Docker creeaza retele izolate pentru ca containerele sa comunice.
208 
209```bash
210# Create a custom network
211docker network create my-network
212 
213# Run containers on the same network
214docker run -d --name api --network my-network my-api
215docker run -d --name db --network my-network postgres:16
216 
217# Containers can reach each other by name
218# From "api" container: postgres://db:5432
219```
220 
221```mermaid
222graph LR
223    subgraph "my-network"
224        API[api container\nport 3000] -- "db:5432" --> DB[db container\nport 5432]
225    end
226    User -- "localhost:3000" --> API
227```
228 
229## Docker Compose
230 
231Docker Compose iti permite sa definesti si sa rulezi aplicatii cu mai multe containere cu un singur fisier YAML.
232 
233### docker-compose.yml
234 
235```yaml
236services:
237  api:
238    build: ./api
239    ports:
240      - "3000:3000"
241    environment:
242      - DATABASE_URL=postgres://user:pass@db:5432/mydb
243    depends_on:
244      - db
245 
246  db:
247    image: postgres:16-alpine
248    environment:
249      - POSTGRES_USER=user
250      - POSTGRES_PASSWORD=pass
251      - POSTGRES_DB=mydb
252    volumes:
253      - pgdata:/var/lib/postgresql/data
254    ports:
255      - "5432:5432"
256 
257  redis:
258    image: redis:7-alpine
259    ports:
260      - "6379:6379"
261 
262volumes:
263  pgdata:
264```
265 
266### Comenzi
267 
268```bash
269# Start all services
270docker compose up -d
271 
272# View logs
273docker compose logs -f
274 
275# Stop all services
276docker compose down
277 
278# Rebuild and restart
279docker compose up -d --build
280 
281# Scale a service
282docker compose up -d --scale api=3
283```
284 
285## .dockerignore
286 
287Ca si `.gitignore`, acest fisier impiedica fisierele inutile sa fie copiate in imagine.
288 
289```plaintext
290node_modules
291.git
292.env
293*.md
294.next
295dist
296coverage
297```
298 
299## Cele Mai Bune Practici pentru Productie
300 
301### 1. Foloseste Imagini de Baza Mici
302 
303```dockerfile
304# Bad: 1GB+
305FROM node:20
306 
307# Good: ~180MB
308FROM node:20-alpine
309```
310 
311### 2. Nu Rula ca Root
312 
313```dockerfile
314FROM node:20-alpine
315RUN addgroup -S app && adduser -S app -G app
316USER app
317WORKDIR /home/app
318COPY --chown=app:app . .
319```
320 
321### 3. Foloseste Tag-uri de Imagine Specifice
322 
323```dockerfile
324# Bad: can change unexpectedly
325FROM node:latest
326 
327# Good: pinned version
328FROM node:20.11-alpine3.19
329```
330 
331### 4. Valorifica Cache-ul de Build
332 
333Ordoneaza instructiunile Dockerfile de la cele mai putin la cele mai frecvent modificate:
334 
335```dockerfile
336FROM node:20-alpine
337WORKDIR /app
338 
339# These change rarely - cached
340COPY package.json package-lock.json ./
341RUN npm ci --only=production
342 
343# This changes often - not cached
344COPY . .
345```
346 
347### 5. Verificari de Sanatate
348 
349```dockerfile
350HEALTHCHECK --interval=30s --timeout=3s --retries=3 \
351  CMD wget -qO- http://localhost:3000/health || exit 1
352```
353 
354### 6. Foloseste Variabile de Mediu
355 
356```dockerfile
357ENV NODE_ENV=production
358ENV PORT=3000
359```
360 
361## Fisa de Referinta pentru Comenzi Docker Comune
362 
363```bash
364# Images
365docker build -t name:tag .        # Build image
366docker images                      # List images
367docker rmi image_name              # Remove image
368docker image prune                 # Remove unused images
369 
370# Containers
371docker run -d -p 3000:3000 image   # Run detached
372docker ps                          # List running
373docker stop container_name         # Stop
374docker rm container_name           # Remove
375docker logs -f container_name      # Follow logs
376docker exec -it container sh       # Shell into container
377 
378# Compose
379docker compose up -d               # Start services
380docker compose down                # Stop services
381docker compose logs -f             # Follow all logs
382docker compose ps                  # List services
383 
384# Cleanup
385docker system prune -a             # Remove everything unused
386```
387 
388## De la Docker la Kubernetes
389 
390Docker gestioneaza containere individuale. Cand trebuie sa orchestrezi sute de containere pe mai multe servere, ai nevoie de Kubernetes. Docker si Kubernetes sunt complementare:
391 
3921. **Docker**: construieste si ruleaza containere
3932. **Kubernetes**: orchestreaza containere la scara (planificare, scalare, auto-vindecare)
394 
395Daca esti interesat de pasul urmator, consulta articolul meu despre Introducere in Kubernetes.
396 
397## Concluzie
398 
399Docker este o abilitate fundamentala pentru dezvoltatorii moderni. Elimina inconsistentele de mediu, simplifica deploy-ul si este fundamentul orchestrarii containerelor cu Kubernetes. Incepe cu un Dockerfile simplu, treci la Docker Compose pentru aplicatii multi-serviciu si adopta build-uri multi-stage si cele mai bune practici de securitate pe masura ce cresti.
400 
401Cel mai bun mod de a invata Docker este sa containerizezi un proiect la care deja lucrezi. Incepe astazi.
402