Yes, Auto Scaling Groups (ASGs) can integrate with Capacity Reservations in AWS, but it’s important to understand how they work together.
How ASG and Capacity Reservations Work Together:
- Capacity Reservations for EC2 Instances:
Capacity Reservations guarantee that a certain number of EC2 instances are available in a specific Availability Zone (AZ) when you need them. You purchase reserved capacity for EC2 instances in a specific AZ, and that capacity is held for your use. - Auto Scaling Group with Capacity Reservation:
You can configure your Auto Scaling Group to launch EC2 instances within a Capacity Reservation. This ensures that when the ASG scales out (launches new instances), the instances are launched into a reserved capacity in the specified AZ, ensuring that your instances are always available and not affected by capacity shortages.
Steps to Use ASG with Capacity Reservations:
- Create a Capacity Reservation: First, you would create a capacity reservation in a specific Availability Zone where your ASG will launch instances.
- Configure the ASG: When creating or modifying your Auto Scaling Group, you can configure it to launch instances in the specific Capacity Reservation you have set up. This ensures that the new instances that the ASG scales out will utilize the reserved capacity in the chosen AZ.
Key Considerations:
- Cost: Even if you configure your ASG to use capacity reservations, you still pay for the reserved capacity whether the instances are fully used or not.
- Capacity Reservation Usage: ASGs can launch instances into capacity reservations, but they can also launch into On-Demand capacity if needed. It’s possible to have a mix, where your ASG launches instances into a Capacity Reservation, but if it scales beyond the reserved capacity, it might launch additional instances using On-Demand capacity.
- Capacity Reservation Sharing: If you are using Capacity Reservations, you can share the reserved capacity across multiple instances, so you aren’t forced to tie it to a specific instance type or size.
Example Scenario:
- You might have an ASG running web servers in a region where there is fluctuating demand. You anticipate peak demand, and to ensure your instances are always available, you create a Capacity Reservation for a certain number of instances in the desired AZ. When the ASG scales out, it will use that reserved capacity first before launching any On-Demand instances.