4.2 - Scaling and high availability on AWS
AWS Certified Cloud Practitioner covers scaling and high availability. Amazon EC2 Auto Scaling automatically adjusts the number of EC2 instances to match application demand, adding capacity under load and removing it when idle. Elastic Load Balancing (ELB) distributes incoming application traffic across multiple targets so no single instance is overwhelmed and unhealthy targets are bypassed. Enabling Multi-AZ deployment for an Amazon RDS database provides a standby replica in another Availability Zone for automatic failover, improving availability rather than read performance. Amazon Route 53 DNS health checks with failover routing can automatically route users away from an unhealthy endpoint to a healthy one. Expect scenario questions that describe matching capacity to demand, spreading traffic, database failover, or DNS-level failover, and ask which service or feature - Auto Scaling, ELB, RDS Multi-AZ or Route 53 failover - achieves it.
Auto add/remove EC2 to match demand = EC2 Auto Scaling. Spread traffic across targets = Elastic Load Balancing. RDS standby in another AZ for failover = Multi-AZ. DNS route away from unhealthy endpoint = Route 53 failover.
Practice questions
1. Which service automatically adjusts the number of EC2 instances to match application demand?
- Amazon Route 53
- Amazon EC2 Auto Scaling (correct answer)
- AWS CloudTrail
- Amazon Redshift
EC2 Auto Scaling adds or removes instances based on demand and policies, improving availability and cost efficiency. Route 53 is DNS; CloudTrail audits API calls; Redshift is a data warehouse.
2. Which service distributes incoming application traffic across multiple targets such as EC2 instances in several AZs?
- Amazon SNS
- AWS Direct Connect
- Elastic Load Balancing (ELB) (correct answer)
- Amazon Glacier
Elastic Load Balancing spreads traffic across healthy targets in multiple AZs, improving fault tolerance and availability. SNS is messaging; Direct Connect is a private link; Glacier is archival storage.
3. Enabling Multi-AZ deployment for an Amazon RDS database primarily provides:
- A standby replica for automatic failover (correct answer)
- Faster read performance across Regions
- Lower storage costs
- Automatic query optimization
RDS Multi-AZ maintains a synchronous standby replica in another AZ and fails over automatically if the primary fails, providing high availability. Read replicas (not Multi-AZ) scale reads.
4. Which Amazon Route 53 feature can route users away from an unhealthy endpoint automatically?
- Bucket versioning
- Reserved capacity
- Cross-region replication
- DNS health checks with failover routing (correct answer)
Route 53 health checks monitor endpoints; with failover routing, DNS stops sending traffic to an unhealthy endpoint and redirects to a healthy one, supporting high availability.
5. To keep a copy of S3 objects in a second AWS Region for resilience, you would enable:
- S3 Transfer Acceleration
- S3 Cross-Region Replication (correct answer)
- S3 Requester Pays
- S3 Object Lock
S3 Cross-Region Replication automatically copies objects to a bucket in another Region, improving resilience and meeting compliance or latency needs. Transfer Acceleration speeds uploads; Object Lock prevents deletion.
6. Which service centralizes and automates backups across AWS services such as EBS, RDS and DynamoDB?
- AWS Snowball
- Amazon EFS
- AWS Backup (correct answer)
- Amazon CloudFront
AWS Backup provides centralized, policy-based backup and restore across many services (EBS, RDS, DynamoDB, EFS and more), simplifying data protection and compliance. Snowball moves data physically; CloudFront is a CDN.