# Explanation: Parallelismi tra Docker Compute e EC2

In questo documento esploreremo come le risorse dei container Docker simulano le istanze EC2 di AWS. Comprendere questi parallelismi ti permetterà di applicare le conoscenze acquisite localmente agli ambienti cloud reali.

---

## Cos'è un'EC2 Instance?

**EC2 (Elastic Compute Cloud)** Instance è una macchina virtuale nel cloud che:
- **Fornisce risorse computazionali**: CPU, memoria, storage, rete
- **Definisce il tipo e la dimensione**: Instance types con diverse combinazioni
- **Scansiona i costi**: Paghi per le risorse che usi (o riservate)

Le istanze EC2 sono il cuore della compute infrastructure in AWS, usate per:
- Web server e application server
- Database (RDS, Aurora)
- Batch processing
- Container hosting (ECS, EKS)

---

## Il Parallelismo Fondamentale

### Container Docker = EC2 Instance

| Locale | Cloud AWS |
|--------|-----------|
| `docker run` | `aws ec2 run-instances` |
| Container con limiti | EC2 Instance type |
| `cpus: '1'` | 1 vCPU |
| `memory: 2G` | 2 GB RAM |
| `docker stats` | CloudWatch Metrics |
| Healthcheck | ELB Health Check |

### Resource Limits = Instance Type

**Locale (Docker Compose):**
```yaml
deploy:
  resources:
    limits:
      cpus: '1'
      memory: 2G
```

**Cloud (AWS CLI):**
```bash
aws ec2 run-instances \
  --image-id ami-12345 \
  --instance-type t2.small \
  # t2.small = 1 vCPU, 2 GB RAM
```

**Stesso risultato:** 1 vCPU, 2 GB RAM di risorse garantite.

---

## EC2 Instance Types - Approfondimento

### Famiglie di Instance Types

AWS offre diverse famiglie di istanze per diversi workload:

| Famiglia | Prefix | Caratteristiche | Docker Parallel |
|----------|--------|-----------------|-----------------|
| **Burstable** | t2, t3 | Credit-based CPU, low cost | Piccoli limiti con burst |
| **General Purpose** | m5, m6 | Equilibrato CPU/memoria | Limiti bilanciati |
| **Compute Optimized** | c5, c6 | Alto ratio CPU | CPU alto, memoria bassa |
| **Memory Optimized** | r5, r6 | Alto ratio memoria | CPU basso, memoria alta |
| **Storage Optimized** | i3, i4 | NVMe SSD locale | Volumes veloci |

### Instance Types Comuni Analizzati

#### T2 Nano - Microservices
**Spec:** 0.5 vCPU, 512 MB RAM
**Costo:** ~$0.006/ora
**Use Case:** Microservizi minimi, background tasks

**Docker Parallel:**
```yaml
deploy:
  resources:
    limits:
      cpus: '0.5'
      memory: 512M
```

**Quando usarlo:**
- Servizi che usano poca CPU
- Task asincroni leggeri
- Sviluppo e test economici

#### T2 Micro - Dev/Test
**Spec:** 1 vCPU, 1 GB RAM
**Costo:** ~$0.012/ora
**Use Case:** Development, test, small websites

**Docker Parallel:**
```yaml
deploy:
  resources:
    limits:
      cpus: '1'
      memory: 1G
```

**Quando usarlo:**
- Ambienti di sviluppo
- Test automation
- Microservices a basso traffico

#### T2 Small - Web Servers
**Spec:** 1 vCPU, 2 GB RAM
**Costo:** ~$0.024/ora
**Use Case:** Web server, API endpoints

**Docker Parallel:**
```yaml
deploy:
  resources:
    limits:
      cpus: '1'
      memory: 2G
```

**Quando usarlo:**
- Web server (Nginx, Apache)
- API REST
- Container reverse proxy

#### T2 Medium - Application Server
**Spec:** 2 vCPU, 4 GB RAM
**Costo:** ~$0.048/ora
**Use Case:** Application server, cache

**Docker Parallel:**
```yaml
deploy:
  resources:
    limits:
      cpus: '2'
      memory: 4G
```

**Quando usarlo:**
- Application server (Node.js, Python)
- Cache server (Redis)
- Database di sviluppo

#### M5 Large - Production
**Spec:** 2 vCPU, 8 GB RAM
**Costo:** ~$0.096/ora
**Use Case:** Production applications

**Docker Parallel:**
```yaml
deploy:
  resources:
    limits:
      cpus: '2'
      memory: 8G
```

**Quando usarlo:**
- Production web applications
- Services con cache in-memory
- Databases di produzione (non critici)

---

## Healthcheck Parallelism

### Docker Healthcheck = ELB Health Check

| Locale | Cloud AWS |
|--------|-----------|
| healthcheck.test | Health check path/protocol |
| healthcheck.interval | Health check interval (30s) |
| healthcheck.timeout | Health check timeout (5s) |
| healthcheck.retries | Unhealthy threshold (2) |
| healthcheck.start_period | Grace period (none in ELB) |

### Esempio Pratico

**Locale (Docker Compose):**
```yaml
healthcheck:
  test: ["CMD", "wget", "--spider", "-q", "http://localhost/health"]
  interval: 30s
  timeout: 5s
  retries: 2
```

**Cloud (Target Group ELB):**
```json
{
  "TargetGroup": {
    "HealthCheckProtocol": "HTTP",
    "HealthCheckPath": "/health",
    "HealthCheckIntervalSeconds": 30,
    "HealthCheckTimeoutSeconds": 5,
    "UnhealthyThresholdCount": 2,
    "HealthyThresholdCount": 2
  }
}
```

**Stesso comportamento:**
- Check HTTP ogni 30 secondi
- Timeout dopo 5 secondi
- Unhealthy dopo 2 fallimenti consecutivi

---

## Resource Monitoring Parallelism

### Docker Stats = CloudWatch Metrics

| Locale | Cloud AWS |
|--------|-----------|
| docker stats | CloudWatch Metrics |
| CPU % | CPUUtilization |
| Mem usage | MemoryUtilization |
| Network I/O | NetworkIn/Out |
| Block I/O | DiskReadBytes/WriteBytes |

### Esempio di Monitoring

**Locale:**
```bash
docker stats lab03-web --no-stream
# lab03-web: 0.01% CPU, 2.5MiB / 1GiB memory (0.24%)
```

**Cloud (CloudWatch):**
```bash
aws cloudwatch get-metric-statistics \
  --namespace AWS/EC2 \
  --metric-name CPUUtilization \
  --dimensions Name=InstanceId,Value=i-12345 \
  --start-time 2024-03-25T00:00:00Z \
  --end-time 2024-03-25T00:05:00Z \
  --period 60 \
  --statistics Average
```

---

## Dipendenze Parallelism

### Docker depends_on = ECS DependsOn

| Locale | Cloud AWS |
|--------|-----------|
| depends_on: service_healthy | dependsOn: condition=HEALTHY |
| depends_on: service_started | dependsOn: condition=START |

### Esempio Multi-Tier

**Locale (Docker Compose):**
```yaml
services:
  web:
    depends_on:
      app:
        condition: service_healthy
  
  app:
    depends_on:
      db:
        condition: service_healthy
  
  db:
    # No dependencies
```

**Cloud (ECS Task Definition):**
```json
{
  "containerDefinitions": [
    {
      "name": "web",
      "dependsOn": [
        {"containerName": "app", "condition": "HEALTHY"}
      ]
    },
    {
      "name": "app",
      "dependsOn": [
        {"containerName": "db", "condition": "HEALTHY"}
      ]
    },
    {
      "name": "db",
      "dependsOn": []
    }
  ]
}
```

---

## Costi e Billing Parallelism

### Docker = Local Resources (Free)

In locale, le risorse Docker sono "gratuite":
- Paghi per l'hardware host (una tantum)
- Nessun costo orario per container
- Limiti servono per isolamento, non billing

### EC2 = Pay-Per-Use

In cloud, paghi per:
- Ore di compute (o secondi con Fargate)
- Tipi di istanza (più grandi = più costosi)
- Riserve e spot instances possono ridurre costi

**Mapping costi:**

| Docker | EC2 | Costo/ora |
|--------|-----|-----------|
| 0.5 CPU, 512M | t2.nano | ~$0.006 |
| 1 CPU, 1G | t2.micro | ~$0.012 |
| 1 CPU, 2G | t2.small | ~$0.024 |
| 2 CPU, 4G | t2.medium | ~$0.048 |
| 2 CPU, 8G | m5.large | ~$0.096 |

---

## Scaling Parallelism

### Docker Compose Scale = EC2 Auto Scaling

**Locale (Horizontal Scaling):**
```yaml
web:
  deploy:
    replicas: 4
    resources:
      limits:
        cpus: '1'
        memory: 2G
```
Risultato: 4 container, ognuno con 1 CPU e 2 GB

**Cloud (Auto Scaling Group):**
```bash
aws autoscaling create-auto-scaling-group \
  --auto-scaling-group-name my-asg \
  --launch-template LaunchTemplateId=lt-12345 \
  --min-size 2 \
  --max-size 4 \
  --desired-capacity 4
```
Risultato: 4 EC2 instances (t2.small)

**Parallelismo:**
- Docker: `replicas` = numero di container
- EC2: `desired-capacity` = numero di istanze
- Entrambi: distribuiscono carico su più unità

---

## Differenze Chiave

### 1. Crediti CPU (Burstable Instances)

**T2/T3 instances** usano CPU credits:
- Ogni istanza accumula crediti quando idle
- Spende crediti quando sotto carico
- Senza crediti = performance degradata

**Docker NON ha credits:**
- CPU limit è hard cap
- Mai degrada (sempre disponibile fino al limite)
- No burst oltre il limite

### 2. Pricing Models

**AWS offre:**
- **On-Demand:** Paghi per ora usata
- **Reserved:** Sconto per 1-3 anni di impegno
- **Spot:** Asta per capacità unused (fino a 90% sconto)
- **Dedicated:** Host fisico dedicato

**Docker:**
- Nessun pricing model
- Tutto flat sul costo host

### 3. Availability Zones

**AWS:**
- Istanze distribuite su multiple AZ
- Ogni AZ = data center separato
- High availability geografica

**Docker:**
- Single host (senza Swarm/Kubernetes)
- Nessuna AZ separation
- Host failure = tutti i container down

---

## Best Practices Transfer

### Da Locale a Cloud

| Best Practice Locale | Equivalente Cloud |
|---------------------|-------------------|
| Set resource limits | Choose right instance type |
| Use healthchecks | Configure ELB health checks |
| depends_on healthy | Use ECS dependsOn |
| Monitor with docker stats | Use CloudWatch alarms |
| Scale with replicas | Use Auto Scaling Groups |

### Evoluzione Architetturale

**Locale (Docker Compose):**
```yaml
services:
  web:
    deploy:
      resources:
        limits:
          cpus: '1'
          memory: 2G
```

**Cloud (ECS/Fargate):**
```json
{
  "containerDefinitions": [{
    "name": "web",
    "cpu": 1024,
    "memory": 2048,
    "memoryReservation": 2048
  }]
}
```

**Nota:** In ECS Fargate, CPU e memoria sono configurati come:
- `cpu`: 256, 512, 1024, 2048, 4096 (unità: 1 vCPU = 1024)
- `memory`: 512, 1024, 2048, ... (in MB)

---

## Command Equivalents Table

| Operazione | Locale (Docker) | Cloud (AWS) |
|------------|------------------|-------------|
| **Deploy compute** | docker compose up -d | aws ec2 run-instances |
| **Check resources** | docker inspect --format '{{.HostConfig}}' | aws ec2 describe-instance-types |
| **Monitor usage** | docker stats | aws cloudwatch get-metric-statistics |
| **Set limits** | deploy.resources.limits | --instance-type parameter |
| **Check health** | docker inspect --format '{{.State.Health.Status}}' | aws elb describe-target-health |
| **Scale out** | docker compose up -d --scale web=4 | aws autoscaling set-desired-capacity |
| **Stop compute** | docker compose stop | aws ec2 stop-instances |
| **Terminate** | docker compose down | aws ec2 terminate-instances |

---

## Conclusione

Le risorse dei container Docker seguono gli stessi principi fondamentali delle EC2 instances: definizione di CPU e memoria, monitoraggio dell'utilizzo, e health checks per verificare lo stato.

Quando lavorerai con EC2 cloud, ricorda:

- **Docker Container** = **EC2 Instance** (unità di compute)
- **Resource Limits** = **Instance Type** (dimensione e potenza)
- **Healthcheck** = **ELB Health Check** (verifica stato)
- **docker stats** = **CloudWatch Metrics** (monitoraggio)
- **depends_on** = **ECS DependsOn** (ordinamento avvio)

Comprendendo questi parallelismi, sarai in grado di progettare architetture cloud scalabili usando le competenze acquisite localmente.

---

## Approfondimenti

- [AWS EC2 Instance Types Documentation](https://docs.aws.amazon.com/ec2/latest/instancetypes/)
- [ECS Task Definitions](https://docs.aws.amazon.com/AmazonECS/latest/developerguide/task_definitions.html)
- [ELB Health Checks](https://docs.aws.amazon.com/elasticloadbalancing/latest/application/target-group-health-checks.html)
- [CloudWatch Metrics](https://docs.aws.amazon.com/AmazonCloudWatch/latest/UserGuide/cloudwatch_concepts.html)