##
**AWS Auto Scaling** is a fully managed service that automatically adjusts the capacity of your AWS resources to maintain steady, predictable performance at the lowest possible cost . It monitors your applications and dynamically adds or removes resources based on real-time demand, ensuring you always have the right amount of capacity .
The service provides a unified interface where you can configure scaling for multiple resource types across different AWS services in one place . You can choose from three built-in optimization strategies: **optimize for performance**, **optimize for costs**, or **balance between the two** .
**Key benefits include**:
- **Automatic resource discovery** - Scans your environment and identifies scalable resources without manual effort
- **Predictive scaling** - Uses machine learning to forecast traffic patterns and provisions capacity in advance of expected spikes
- **Smart scaling policies** - Self-optimizing target tracking that learns actual load patterns to minimize fluctuations
**Important**: AWS Auto Scaling itself is **free** - you only pay for the underlying AWS resources (EC2 instances, DynamoDB capacity, etc.) and CloudWatch monitoring fees .
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## AWS Auto Scaling for Different Services
Here's how auto scaling works for each service you asked about, including what specifically gets scaled:
### Amazon EC2 Auto Scaling Groups
| Aspect | Details |
|--------|---------|
| **What gets scaled** | Number of EC2 instances in the Auto Scaling group |
| **Scales by** | Launching or terminating EC2 instances |
| **Scalable dimension** | `autoscaling:autoScalingGroup:DesiredCapacity` |
| **How it works** | You define minimum and maximum instance counts. When demand increases (e.g., CPU utilization rises), ASG launches new instances. When demand drops, it terminates excess instances |
| **Scaling policies** | Target tracking (e.g., keep CPU at 50%), step scaling (e.g., add 2 instances when CPU > 70%), scheduled scaling (e.g., scale out at 9 AM) |
### Amazon EC2 Spot Fleet Requests
| Aspect | Details |
|--------|---------|
| **What gets scaled** | Target capacity of the Spot Fleet (number of instances) |
| **Scales by** | Launching or terminating Spot Instances |
| **Scalable dimension** | `ec2:spot-fleet-request:TargetCapacity` |
| **How it works** | Automatically adjusts the fleet size based on demand. Also **automatically replaces instances** that get interrupted due to price or capacity changes |
| **Key benefit** | Maintains desired capacity even when Spot Instances are reclaimed, helping you balance cost savings with availability |
### Amazon ECS (Elastic Container Service)
| Aspect | Details |
|--------|---------|
| **What gets scaled** | Desired task count for an ECS service |
| **Scales by** | Increasing or decreasing the number of running tasks |
| **Scalable dimension** | `ecs:service:DesiredCount` |
| **How it works** | When CPU or memory utilization of your service increases, ECS launches more tasks (containers). When utilization drops, it terminates tasks |
| **Use case** | Microservices that need to handle variable request loads without over-provisioning |
### Amazon DynamoDB (Table or Global Secondary Index)
| Aspect | Details |
|--------|---------|
| **What gets scaled** | Provisioned read and write capacity units |
| **Scales by** | Increasing or decreasing RCU and WCU settings |
| **Scalable dimensions** | `dynamodb:table:ReadCapacityUnits`, `dynamodb:table:WriteCapacityUnits`, `dynamodb:index:ReadCapacityUnits`, `dynamodb:index:WriteCapacityUnits` |
| **How it works** | DynamoDB Auto Scaling monitors consumed capacity vs. provisioned capacity. When utilization exceeds target (e.g., 70%), it increases provisioned capacity to prevent throttling. When utilization drops, it decreases capacity to save costs |
| **Key benefit** | Prevents throttling during traffic spikes without manual intervention |
**For DynamoDB**: The scaling is handled through **Application Auto Scaling** (the underlying service for non-EC2 resources) and can be configured for both the main table and any Global Secondary Indexes .
### Amazon Aurora
| Aspect | Details |
|--------|---------|
| **What gets scaled** | Number of Aurora Replicas (read replicas) in the DB cluster |
| **Scales by** | Dynamically adding or removing Aurora Replicas |
| **Scalable dimension** | `rds:cluster:ReadReplicaCount` |
| **How it works** | When active connections or workload increases, Aurora automatically provisions additional read replicas to handle the load. When demand drops, it removes excess replicas |
| **Supported editions** | Aurora MySQL-compatible and Aurora PostgreSQL-compatible |
| **Use case** | Read-heavy applications where read replicas offload SELECT queries from the primary writer instance |
**Important note for Aurora**: Auto scaling applies to **read replicas only**. The primary writer instance (handling writes) is not automatically scaled - you would need to manually upgrade its instance class or use Aurora Serverless for write scaling .
---
## Comparison Table: What Gets Scaled
| Service | What Scales | Scaling Action | Scalable Dimension |
|---------|-------------|----------------|---------------------|
| **EC2 Auto Scaling** | EC2 instances | Launch/terminate | DesiredCapacity |
| **Spot Fleet** | Spot Instances | Launch/terminate | TargetCapacity |
| **ECS** | Container tasks | Increase/decrease task count | DesiredCount |
| **DynamoDB** | Read/write capacity units | Adjust RCU/WCU | ReadCapacityUnits/WriteCapacityUnits |
| **Aurora** | Read replicas | Add/remove replicas | ReadReplicaCount |
---
## How to Configure Auto Scaling
### Option 1: Using AWS Auto Scaling Console (Scaling Plans)
1. Go to AWS Auto Scaling console
2. Create a **scaling plan** - this discovers all your scalable resources automatically
3. Choose your scaling strategy (optimize for availability, cost, or balance)
4. AWS Auto Scaling automatically creates the scaling policies and CloudWatch alarms for you
### Option 2: Service-Specific Configuration
- **EC2**: Configure directly in Auto Scaling Groups console
- **DynamoDB**: Enable Auto Scaling in the DynamoDB console for each table/index
- **Aurora**: Configure in RDS console under the DB cluster settings
- **ECS**: Set up Service Auto Scaling in ECS console
### Option 3: Infrastructure as Code (CDK)
The AWS CDK provides constructs for Application Auto Scaling to configure scaling for all non-EC2 resources :
```typescript
// Example for DynamoDB
const readCapacity = table.autoScaleReadCapacity({
minCapacity: 10,
maxCapacity: 1000
});
readCapacity.scaleOnUtilization({
targetUtilizationPercent: 60
});
```
---
## Summary
AWS Auto Scaling unifies scaling across five key service types:
- **EC2 Auto Scaling Groups** - Scales EC2 instances
- **Spot Fleets** - Scales Spot Instances with automatic replacement
- **ECS** - Scales container tasks
- **DynamoDB** - Scales table/index read/write capacity
- **Aurora** - Scales read replica count
Each service scales a different dimension, but all follow the same principle: automatically match capacity to demand, reduce costs during low traffic, and maintain performance during spikes .
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