Multi-AZ

💡 Definition

Multi-AZ (Availability Zone) deployments allow you to run your resources (like databases or instances) in more than one AZ to provide high availability and failover support.

🔑 Key Concepts

• High Availability: If one AZ goes down, your application can failover to another AZ without manual intervention.
• Synchronous Replication: For services like RDS, data is written to the primary and standby DB concurrently to ensure data integrity.
• Automatic Failover: In the event of a failure (hardware, network, etc.), AWS automatically promotes the standby to primary.

⚙️ How it Works

1. Deploy: You enable Multi-AZ when creating a resource (e.g., an RDS instance).
2. Replicate: AWS creates a standby instance in a different AZ.
3. Monitor: AWS monitors the health of the primary instance.
4. Failover: If the primary fails, AWS flips the DNS record to point to the standby.

🎯 Use Cases

• Production Databases: Protecting critical data from infrastructure failure.
• Highly Available Apps: Ensuring web servers are running in at least 2 AZs behind a Load Balancer.

💰 Pricing Model

• Cost: Typically costs more (often double for RDS) because you are running two instances instead of one.

📝 Exam Tips (CLF-C02)

• Multi-AZ is primarily for High Availability (HA) and Disaster Recovery (DR).
• Contrast with Read Replicas, which are for Scaling Read Performance.
• Synchronous replication ensures no data loss during failover.

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See Also: * RDS * High Availability * Fault Tolerance