This content originally appeared on DEV Community and was authored by Samia Khan
This post will go over the basics of automating EC2 instance provisioning through the use of launch templates, auto scaling groups and load balancers.
What are Launch Templates?
Launch templates are reusable configuration templates for launching EC2 instances. They allow you to specify how you want your instances to be deployed by defining the AMI, instance type, security groups, user data etc and are especially useful in Auto Scaling groups, Spot Fleets, and EC2 Fleet setups.
Benefits:
- Allows for consistency across instances provisioned by ensuring that resources are created with the required configurations.
- Reduces the risk of errors and misconfiguration by using predefined templates.
- Easily manage and update the configuration of your EC2 instances by updating the launch template and new instances created from the template will inherit the updated changes
- Template versioning improves version control by allowing you to track changes made to a template and revert to earlier versions if needed.
What is an Auto Scaling Group?
An Auto Scaling Group (ASG) uses launch templates to automatically launch or terminate EC2 instances based on user-defined policies to ensure applications have the right amount of capacity to handle traffic.
Scaling types:
Manual scaling - Manually increase or decrease instance count
Dynamic Scaling - Automatically adjusts capacity based on metrics like CPU, memory, or custom metrics
Scheduled Scaling - Scales at specific times (e.g. add 5 EC2s every Monday at 9 AM)
Predictive Scaling - Uses machine learning to forecast traffic and scale in advance
Benefits:
High availability - Ensures enough instances are running to meet demand
Cost-efficiency - Terminates unnecessary instances when demand is low
Fault tolerance - Automatically replaces failed instances
Elasticity - Adds or removes EC2s based on metrics like CPU
What is an Application Load Balancer?
An Application Load Balancer (ALB) accepts incoming traffic from clients and distributes it across various targets such as EC2 instances.
Benefits:
- ALB automatically spreads traffic across multiple Availability Zones, ensuring your application remains available even if one AZ fails.
- Works seamlessly with ASGs by updating the target group to only send traffic to healthy instances as they scale up and down.
- Allows for advanced routing based on paths, headers and and hostnames which enables microservices and multiple apps on a single EC2 to share the same ALB.
What is a Target Group?
A target group is a group of resources (targets) that a load balancer routes traffic to. You can define the health check settings for the targets, the port and protocol to use to route traffic and the target type such as EC2, IP address, Lambda or Application Load Balancer. It is the bridge between a load balancer and your application infrastructure.
How does it work?
When you register a target e.g. EC2 instances to a target group, you can attach the group to a listener rule on an ALB, NLB, or Gateway Load Balancer. When a request hits the load balancer, it uses listener rules to match the request and forward it to the appropriate target group. Health checks are used to monitor target availability. If a target fails, it is automatically removed from routing.
How do these services work together?
When you create a launch template to define your EC2 configuration, an ASG uses this template to launch instances based on the min, max and desired capacity specified. The ALB doesn't send traffic directly to your ASG, it does this through an ALB listener rule which forwards the request to the Target Group.
In summary:
1️⃣ A user accesses your app via the ALB DNS name.
2️⃣ ALB receives the request on port 80 or 443.
3️⃣ ALB listener rule forwards request to the Target Group.
4️⃣ Target Group checks which EC2s are healthy.
5️⃣ Target Group sends the request to one of the healthy EC2s in the ASG.
6️⃣ ASG monitors performance and scales EC2s up or down using the Launch Template.
This content originally appeared on DEV Community and was authored by Samia Khan
Samia Khan | Sciencx (2025-07-08T17:28:06+00:00) AWS Auto Scaling and Load Balancing Basics. Retrieved from https://www.scien.cx/2025/07/08/aws-auto-scaling-and-load-balancing-basics/
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