How to set up auto-scaling groups in AWS

Short answer

Create an Auto Scaling group (ASG) tied to a launch template that defines the EC2 instance configuration. Attach scaling policies based on CloudWatch metrics (CPU, request count) or schedules to add or remove instances automatically.

Details

An ASG maintains a desired capacity within minimum and maximum bounds. It replaces unhealthy instances detected via EC2 status checks or Elastic Load Balancer health checks. Target tracking policies are the simplest: you set a metric target (e.g., 50% CPU) and AWS adjusts capacity to maintain it. Step scaling and simple scaling offer more control but require careful tuning.

For stateless applications, pair ASGs with Application Load Balancers and store session data externally. If you are building the underlying application in Node.js, see How to implement rate limiting in Express.js to protect scaled instances from traffic spikes. For multi-region resilience, review How to design a multi-region architecture on AWS.

Tips

• Use lifecycle hooks to gracefully drain connections before termination.
• Warm up new instances with custom scripts in user data before they receive traffic.
• Combine predictive scaling with dynamic scaling for workloads with predictable daily patterns.