Here is step by step guide as how to change launch configuration to launch template in AWS for an autoscaling group. It's actually quite simple and straight forward.
There has been a notification in AWS that was sent out this week to following accounts that make use of Amazon EC2 Auto Scaling launch configurations. Amazon EC2 Launch Configurations will Deprecate support for new Instances. After December 31, 2022 no new Amazon Elastic Compute Cloud (Amazon EC2) instance types will be added to launch configurations. After this date, existing launch configurations will continue to work, but new EC2 instances will only be supported through launch templates.
In order to update the ASG, you need to follow below steps:
1. Create a launch template and paste the user data scripts in it and save it. Also, make sure that you are using the correct AMI ID in it.
2. Once launch template is created then navigate your respective auto scaling group and in the details section of the ASG, click on "edit" button in the launch configuration section. There you will get an option on the top like "Switch to Launch Template".
3. Then select your newly created launch template and save the changes
Here is the document to create launch template.
Here is the document to know how to replace a launch configuration with a launch template.
The existing instances will keep in running state. Only new instances will be launched using launch template. On the ASG console, you can check the instance is launched using launch template in the instance management section.
For the instances perspective testing like application is running or not or instance is working properly or not, for this you can login the instance and verify the details. It will not automatically launch an instance in the ASG after setting it to launch template. you would have to change the desired capacity to launch a new instance using the launch template.