उच्च उपलब्धता (HA) म्हणजे सिस्टमचे अपयशातून अपरिवर्तनीय राहणे — रिडंडन्सी, मल्टी-AZ डिप्लॉयमेंट, ऑटो-रिकव्हरी आणि एकल अपयश पॉइंटस् काढून टाकून. हे प्रोडक्शन सिस्टमचे मूलभूत लक्ष्य आहे आणि AWS आर्किटेक्चरचे मुख्य क्षेत्र आहे.
मुख्य HA तत्त्वे
✓ ELIMINATE SINGLE POINTS OF FAILURE — no single component whose failure takes down
the system → redundancy everywhere (multiple instances, AZs, etc.)
✓ Deploy across MULTIPLE AVAILABILITY ZONES — survive an AZ (data center) failure
✓ AUTOMATIC RECOVERY — detect failures and recover/replace automatically (no manual fix)
✓ DECOUPLE components — failures isolated; one component's failure doesn't cascade
AWS वर HA तंत्रे
COMPUTE → Auto Scaling Group across multiple AZs + Load Balancer
→ instances spread across AZs; LB health checks route around failures; ASG replaces
failed instances → survives instance AND AZ failures
DATABASE → RDS Multi-AZ (synchronous standby in another AZ, auto-failover);
read replicas; DynamoDB (multi-AZ by default)
STORAGE → S3 (multi-AZ durable by design); EBS snapshots
DNS → Route 53 failover routing + health checks (route to healthy/backup endpoints)
DECOUPLING → SQS queues (buffer; consumers can fail/retry without losing work)
