5.1.3. Auto Scaling for Elasticity and HA

💡 First Principle: AWS Auto Scaling dynamically adjusts EC2 instance capacity to meet fluctuating application demand, ensuring consistent performance, high availability, and optimal cost-efficiency.

Scenario: You need to deploy a web application that experiences unpredictable traffic spikes throughout the day and night. You want to ensure the application maintains consistent performance during peaks while minimizing costs during lulls, and automatically replace any unhealthy instances.

AWS Auto Scaling is a service that monitors your applications and automatically adjusts capacity to maintain steady, predictable performance at the lowest possible cost. For SysOps Administrators, it's crucial for achieving both elasticity and high availability.

Key Concepts of Auto Scaling:

• Auto Scaling Group (ASG): (A collection of EC2 instances that are treated as a logical grouping for automatic scaling and management.) Manages a fleet of EC2 instances and ensures they are distributed across Availability Zones for high availability.
• Elasticity: ASGs automatically add instances (scale out) during periods of high demand and remove instances (scale in) during low demand, matching capacity to actual workload.
• High Availability: If an EC2 instance becomes unhealthy or terminates, the ASG automatically replaces it, ensuring the desired capacity is maintained.
• Launch Templates/Configurations: Define how new instances are launched within the ASG (e.g., AMI, instance type, Security Groups).
• Scaling Policies: Define how to scale. Common types include:
  • Target Tracking Scaling: Maintains a specified target value for a metric (e.g., 50% CPU utilization).
  • Simple/Step Scaling: Responds to a CloudWatch alarm by adding/removing a fixed number of instances.
  • Scheduled Scaling: Scales based on a predictable schedule.
• Health Checks: ASGs monitor instance health and replace unhealthy ones.

⚠️ Common Pitfall: Not configuring a "scale-in" policy, leading to over-provisioned resources and unnecessary costs during low demand.

Key Trade-Offs: Automated scaling (Auto Scaling, efficient, HA) versus manual scaling (simpler for static loads, but inefficient and not HA for dynamic loads).

Reflection Question: How does AWS Auto Scaling, particularly through its Auto Scaling Groups and scaling policies, fundamentally enable elasticity and high availability for your application by dynamically adjusting EC2 instance capacity and replacing unhealthy instances?