i have 1 instances and i am using application load balancer

Hello,

If you are connecting to a single instance from clients it is a SPOF (Single Point of Failure) design, if you use a load balancer you can scale your Web/App fleet and achieve high availability.

As for which one to choose (ALB Vs NLB) see below link for the key differences between the two.

https://aws.amazon.com/elasticloadbalancing/features/

Hello,

1. is there any specific reason you are using application running on only one instance ?
2. I would recommend you to have Load balancer (ALB or NLB) based on your use case and have two ec2 instance in different Availability zone.
3. Also launch the instances using AWS Autoscaling (ASG) .
4. In the Autoscaling, have the health check as Load balancer, so that when loadbalancer marks any instance as unhealthy, ASG terminates the instance and launch instance new instance , also it attach the new instance back to the load balancer .

Web Application Hosting in the AWS Cloud.

AWS Serverless Multi-Tier Architectures with Amazon API Gateway and AWS Lambda