Auto Scaling Groups (ASGs) and Managed Instance Groups (MIGs)
Auto Scaling Groups (ASGs) and Managed Instance Groups (MIGs) are mechanisms provided by cloud service providers to automatically manage the scaling of virtual machines based on predefined criteria, ensuring that applications maintain optimal performance and availability. ASGs are associated with Amazon Web Services (AWS), while MIGs are related to Google Cloud Platform (GCP).
Auto Scaling Groups (ASGs) in AWS
Description: ASGs in AWS allow you to automatically scale the number of Amazon EC2 instances based on demand. They help ensure that you have the right number of EC2 instances available to handle the load for your application.
Key Concepts:
- Launch Configuration/Template: Defines the EC2 instance configuration, including instance type, AMI, key pair, security groups, and other parameters.
- Scaling Policies: Define how the ASG should scale in or out. Policies can be based on metrics (e.g., CPU utilization) or scheduled actions.
- Desired Capacity: The number of instances the ASG should attempt to maintain.
- Min and Max Size: The minimum and maximum number of instances that the ASG can scale to.
Benefits:
- Automatic Scaling: Automatically adjusts the number of instances based on demand.
- High Availability: Distributes instances across multiple availability zones to improve fault tolerance.
- Cost Efficiency: Scales out to meet demand and scales in to reduce costs during low demand periods.
Example:
-
Create a Launch Configuration/Template:
aws autoscaling create-launch-configuration --launch-configuration-name my-launch-config --image-id ami-12345678 --instance-type t2.micro -
Create an Auto Scaling Group:
aws autoscaling create-auto-scaling-group --auto-scaling-group-name my-asg --launch-configuration-name my-launch-config --min-size 1 --max-size 10 --desired-capacity 2 --vpc-zone-identifier subnet-abcde1234 -
Define a Scaling Policy:
aws autoscaling put-scaling-policy --auto-scaling-group-name my-asg --policy-name scale-out --scaling-adjustment 1 --adjustment-type ChangeInCapacity
Managed Instance Groups (MIGs) in GCP
Description: MIGs in GCP allow you to manage groups of homogeneous instances, making it easy to apply load balancing, autoscaling, and updates to a set of instances.
Key Concepts:
- Instance Template: Defines the configuration for the instances in the group, including machine type, boot disk image, and other properties.
- Autoscaling Policies: Define how the MIG should scale based on metrics like CPU utilization or custom metrics.
- Target Size: The number of instances that the MIG should maintain.
- Health Checks: Ensures that the instances are healthy and replaces any unhealthy instances.
Benefits:
- Automated Management: Automatically handles instance scaling, health checking, and updates.
- High Availability: Distributes instances across multiple zones for resilience.
- Cost Management: Adjusts the number of instances based on real-time demand.
Example:
-
Create an Instance Template:
gcloud compute instance-templates create my-template --machine-type n1-standard-1 --image-family debian-9 --image-project debian-cloud -
Create a Managed Instance Group:
gcloud compute instance-groups managed create my-mig --base-instance-name my-instance --size 2 --template my-template --zones us-central1-a,us-central1-b -
Set Autoscaling Policy:
gcloud compute instance-groups managed set-autoscaling my-mig --max-num-replicas 10 --target-cpu-utilization 0.75 --cool-down-period 90
Comparison Summary
| Feature | Auto Scaling Groups (ASGs) in AWS | Managed Instance Groups (MIGs) in GCP |
|---|---|---|
| Configuration | Launch Configuration/Template | Instance Template |
| Scaling Policies | Metrics-based (e.g., CPU, RAM) and Scheduled Scaling | Metrics-based (e.g., CPU, custom metrics) |
| Health Checks | EC2 status checks, Elastic Load Balancing (ELB) health checks | Health checks configured within MIG |
| Fault Tolerance | Distributes instances across Availability Zones (AZs) | Distributes instances across Zones |
| Integration | Integrated with AWS services like ELB, CloudWatch, SNS | Integrated with GCP services like Load Balancer, Stackdriver |
| Dynamic Management | Adjusts instance count based on policies | Adjusts instance count and performs rolling updates |