Introduction:

This is a guide for implementing a Dynamic Auto-Scaling Web Application Deployment with Public IP Display.

Explanation:

AWS ALB is a feature of Elastic Load Balancing.
Traffic Distribution: They automatically distribute traffic to healthy targets (such as: EC2 instances, containers, IP addresses, in one or more Availability Zones (AZs)), improving application availability and responsiveness.
Traffic Routing: It operates at the application level (Layer 7) of the OSI model, allowing it to route traffic based on the content of the request, including the host and path.

AWS ASG is a key component of AWS’s scalable infrastructure.
Dynamic Scaling: ASGs can scale out (increase the number of instances) and scale in (decrease the number of instances) based on predefined policies and metrics, such as CPU utilization or network traffic.
Launch Configurations and Templates: These define how new instances are launched, including the AMI (Amazon Machine Image), instance type, and security groups.
Traffic Distribution: ASGs automatically register new instances with a load balancer, distributing traffic evenly across all instances.
Cost Optimization: You only pay for the EC2 instances that are spun up and down, and ASGs themselves are free.
Monitoring: You can monitor ASGs in the AWS Management Console to see instances scaling in and out based on the load.

Test the entire setup by generating load on the ALB:
- EC2 dashboard -> Load Balancing -> Load Balancers -> Select the ALB created and copy the DNS name details, paste it on a browser tab and load the page.
Verify that the ASG responds dynamically to the increased load by scaling out,
Confirm that the ASG also scales in automatically when the load decreases:
- To see changes:
  - EC2 Dashboard -> Auto Scaling -> Auto Scaling Groups -> Select your ASG -> Monitoring -> Auto Scaling -> Watch the graphs.
  - EC2 Dashboard -> See the Running Instances.
- To create instant changes:
  - EC2 Dashboard -> Auto Scaling -> Auto Scaling Groups -> Select your ASG -> Edit and change instances capacity.
Check the index.html file on instances to ensure that it displays the public IP dynamically:
- EC2 Dashboard -> Select a running instance -> Connect -> EC2 Instance Connect -> Connect.
- To see it displays the public IP of this instance:
```
cat /var/www/html/index.html
```
- You can do the same with other running instances and see it displays their public IP individualy.
- To see that it displays the public IP dynamically:
  - EC2 dashboard -> Load Balancing -> Load Balancers -> Select the ALB created and copy the DNS name details, paste it on a browser tab and load the page.
  - Refreshing the page will give us a different public IP (depending on how many instances are running).

Author: LuciaHeredia