Auto Scaling & Load Balancing

25 minLesson 4 of 5

Learning Objectives

  • ✓Create and configure Auto Scaling Groups
  • ✓Define scaling policies (target tracking, step, scheduled)
  • ✓Set up Application Load Balancers
  • ✓Implement health checks and high availability

Auto Scaling Overview

Auto Scaling automatically adjusts the number of EC2 instances based on demand.

┌─────────────────────────────────────────────┐
│           Auto Scaling Group                 │
│                                             │
│  Min: 2    Desired: 3    Max: 10            │
│                                             │
│  ┌──────┐  ┌──────┐  ┌──────┐              │
│  │ EC2  │  │ EC2  │  │ EC2  │  ← Current   │
│  └──────┘  └──────┘  └──────┘              │
│                                             │
│  Scale Out ──▶ when CPU > 70%               │
│  Scale In  ──▶ when CPU < 30%               │
└─────────────────────────────────────────────┘

Components

ComponentPurpose
Launch TemplateInstance configuration (AMI, type, SG)
Auto Scaling GroupManages instance count
Scaling PolicyWhen and how to scale
Health CheckDetect unhealthy instances

Launch Template

aws ec2 create-launch-template \
  --launch-template-name nextgen-web-template \
  --version-description "v1" \
  --launch-template-data '{
    "ImageId": "ami-0c55b159cbfafe1f0",
    "InstanceType": "t3.small",
    "KeyName": "nextgen-key",
    "SecurityGroupIds": ["sg-0123456789abcdef0"],
    "UserData": "'$(base64 -w0 userdata.sh)'",
    "TagSpecifications": [{
      "ResourceType": "instance",
      "Tags": [{"Key": "Name", "Value": "nextgen-web"}]
    }]
  }'

Auto Scaling Group

aws autoscaling create-auto-scaling-group \
  --auto-scaling-group-name nextgen-web-asg \
  --launch-template LaunchTemplateName=nextgen-web-template,Version='$Latest' \
  --min-size 2 \
  --max-size 10 \
  --desired-capacity 3 \
  --availability-zones us-east-1a us-east-1b us-east-1c \
  --target-group-arns arn:aws:elasticloadbalancing:... \
  --health-check-type ELB \
  --health-check-grace-period 300

Scaling Policies

# Keep average CPU at 60%
aws autoscaling put-scaling-policy \
  --auto-scaling-group-name nextgen-web-asg \
  --policy-name cpu-target-tracking \
  --policy-type TargetTrackingScaling \
  --target-tracking-configuration '{
    "PredefinedMetricSpecification": {
      "PredefinedMetricType": "ASGAverageCPUUtilization"
    },
    "TargetValue": 60.0,
    "ScaleInCooldown": 300,
    "ScaleOutCooldown": 60
  }'

Step Scaling

# Scale based on CPU thresholds
aws autoscaling put-scaling-policy \
  --auto-scaling-group-name nextgen-web-asg \
  --policy-name cpu-step-scaling \
  --policy-type StepScaling \
  --adjustment-type ChangeInCapacity \
  --step-adjustments '[
    {"MetricIntervalLowerBound": 0, "MetricIntervalUpperBound": 20, "ScalingAdjustment": 1},
    {"MetricIntervalLowerBound": 20, "ScalingAdjustment": 3}
  ]'

Scheduled Scaling

# Scale up for business hours
aws autoscaling put-scheduled-update-group-action \
  --auto-scaling-group-name nextgen-web-asg \
  --scheduled-action-name scale-up-morning \
  --recurrence "0 8 * * MON-FRI" \
  --desired-capacity 5
 
# Scale down at night
aws autoscaling put-scheduled-update-group-action \
  --auto-scaling-group-name nextgen-web-asg \
  --scheduled-action-name scale-down-night \
  --recurrence "0 20 * * MON-FRI" \
  --desired-capacity 2

Application Load Balancer

# Create ALB
aws elbv2 create-load-balancer \
  --name nextgen-alb \
  --subnets subnet-aaa subnet-bbb subnet-ccc \
  --security-groups sg-0123456789abcdef0 \
  --scheme internet-facing \
  --type application
 
# Create target group
aws elbv2 create-target-group \
  --name nextgen-web-tg \
  --protocol HTTP \
  --port 80 \
  --vpc-id vpc-0123456789abcdef0 \
  --health-check-path /health \
  --health-check-interval-seconds 30 \
  --healthy-threshold-count 2 \
  --unhealthy-threshold-count 3
 
# Create listener
aws elbv2 create-listener \
  --load-balancer-arn arn:aws:elasticloadbalancing:... \
  --protocol HTTP \
  --port 80 \
  --default-actions Type=forward,TargetGroupArn=arn:aws:elasticloadbalancing:...

Path-Based Routing

# Route /api/* to API target group
aws elbv2 create-rule \
  --listener-arn arn:aws:elasticloadbalancing:... \
  --priority 10 \
  --conditions '[{"Field":"path-pattern","Values":["/api/*"]}]' \
  --actions '[{"Type":"forward","TargetGroupArn":"arn:aws:elasticloadbalancing:..."}]'

High Availability Architecture

┌─────────────────────────────────────────────┐
│              Application Load Balancer        │
└──────┬──────────────┬──────────────┬────────┘
       │              │              │
┌──────▼─────┐ ┌─────▼──────┐ ┌────▼───────┐
│   AZ-1a    │ │   AZ-1b    │ │   AZ-1c    │
│  ┌──────┐  │ │  ┌──────┐  │ │  ┌──────┐  │
│  │ EC2  │  │ │  │ EC2  │  │ │  │ EC2  │  │
│  └──────┘  │ │  └──────┘  │ │  └──────┘  │
└────────────┘ └────────────┘ └────────────┘

Summary

You've learned:

  • Auto Scaling Groups for dynamic capacity
  • Scaling policies (target tracking, step, scheduled)
  • Application Load Balancer setup and routing
  • Health checks and high availability patterns
  • Multi-AZ architecture for fault tolerance

Next Steps

Next, we'll explore AWS networking with VPCs, subnets, and security architecture.

Amazon CloudWatch — Monitoring & AlarmsVPC Networking & Security Architecture