Traffic: 1,000 req/min
Users: 10,000 active
Data: 100GB database
Response time: p95 = 500ms

CREATE INDEX idx_users_email ON users(email);
CREATE INDEX idx_orders_user_created ON orders(user_id, created_at);

const cached = await redis.get(`user:${userId}`);
if (cached) return JSON.parse(cached);

const user = await db.users.findById(userId);
await redis.setex(`user:${userId}`, 3600, JSON.stringify(user));

Write Load: Primary DB
Read Load: 3x Read Replicas

ALB
 ├── Server 1
 ├── Server 2
 └── Server 3

// Before: Sync
await sendEmail(user);
await processPayment(order);
await updateAnalytics(event);
return response; // Waits 5+ seconds

// After: Async
await queue.add("send-email", { userId });
await queue.add("process-payment", { orderId });
await queue.add("update-analytics", { event });
return response; // Returns immediately

Shard 1: user_id 0-24999
Shard 2: user_id 25000-49999
Shard 3: user_id 50000-74999
Shard 4: user_id 75000-99999

Service A → Kafka → Service B
          ↘        ↗ Service C

| Metric           | Current | Warning | Critical | Action                  |
| ---------------- | ------- | ------- | -------- | ----------------------- |
| CPU              | 40%     | 70%     | 85%      | Add servers             |
| Memory           | 50%     | 75%     | 90%      | Upgrade instances       |
| DB Connections   | 20      | 40      | 50       | Add read replicas       |
| Query Time (p95) | 200ms   | 500ms   | 1000ms   | Add indexes             |
| Queue Depth      | 100     | 1000    | 5000     | Add workers             |
| Error Rate       | 0.1%    | 1%      | 5%       | Investigate immediately |

# Current baseline
hey -n 10000 -c 100 https://api.example.com/users

# Target 10x
hey -n 100000 -c 1000 https://api.example.com/users

# Measure:
# - Requests/sec
# - p50, p95, p99 latency
# - Error rate
# - Resource utilization

| Strategy      | Cost/Month | Expected Impact    | ROI | Priority |
| ------------- | ---------- | ------------------ | --- | -------- |
| DB Indexes    | $0         | 80% faster queries | ∞   | HIGH     |
| Redis Cache   | $50        | 60% less DB load   | 12x | HIGH     |
| Read Replicas | $300       | 3x capacity        | 10x | MEDIUM   |
| Load Balancer | $400       | 3x throughput      | 7x  | MEDIUM   |
| DB Sharding   | $1,200     | 4x capacity        | 3x  | LOW      |