Auto Scaling Cheat Sheet

Explains horizontal vs vertical scaling, scaling policies, cooldowns, and AWS Auto Scaling Group configuration with practical CLI examples.

2 PagesIntermediateJan 25, 2026

Core Concepts

Fundamental auto scaling terminology.

Horizontal Scaling (Scale Out/In)- Adding or removing instances/nodes to handle load
Vertical Scaling (Scale Up/Down)- Increasing or decreasing the resources (CPU/RAM) of an existing instance
Auto Scaling Group (ASG)- AWS construct that manages a fleet of EC2 instances between min/max/desired capacity
Launch Template- Defines instance configuration (AMI, instance type, security groups) used by an ASG
Cooldown Period- Time after a scaling activity during which further scaling actions are suppressed
Warm-up Time- Time a new instance needs before it counts toward aggregated metrics

Scaling Policy Types

Different strategies for triggering scaling actions.

Target Tracking- Maintains a metric (e.g. CPU 50%) automatically, similar to a thermostat
Step Scaling- Adds/removes capacity in steps based on the size of the alarm breach
Simple Scaling- Single scaling adjustment triggered by a CloudWatch alarm, then waits for cooldown
Scheduled Scaling- Scales at predictable times, e.g. business hours or known traffic spikes
Predictive Scaling- Uses ML forecasts of historical traffic patterns to scale ahead of demand

Create an Auto Scaling Group (AWS CLI)

Provision an ASG with min/max/desired capacity across subnets.

bash

aws autoscaling create-auto-scaling-group \  --auto-scaling-group-name my-asg \  --launch-template LaunchTemplateName=my-template,Version='$Latest' \  --min-size 2 \  --max-size 10 \  --desired-capacity 3 \  --vpc-zone-identifier "subnet-abc123,subnet-def456" \  --health-check-type ELB \  --health-check-grace-period 120

Target Tracking Policy

Keep average CPU utilization near 50% automatically.

bash

aws autoscaling put-scaling-policy \  --auto-scaling-group-name my-asg \  --policy-name cpu-target-tracking \  --policy-type TargetTrackingScaling \  --target-tracking-configuration '{    "PredefinedMetricSpecification": {      "PredefinedMetricType": "ASGAverageCPUUtilization"    },    "TargetValue": 50.0  }'

Pro Tip

Combine target tracking with a scheduled minimum capacity for known traffic spikes (e.g. Black Friday) — reactive policies alone often lag behind sudden demand surges.

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