Using a combination of Terraform and Ansible to create dynamic AWS EC2 infrastructure
There are a lot of gaps in your deployment and configuration strategy. In order to provide a more robust and elegant strategy, I suggest you:

Define autoscaling groups with Terraform instead of provisioning individual EC2 instances. Auto-scaling groups make dynamically scaling instances a much simpler process. It will also allow you to define scaling policies and health checks for your instances to determine when to add/remove instances from your autoscaling group.
Create and define CloudWatch Metrics and CloudWatch Alarms. CloudWatch allows you to create custom metrics to monitor and alert via CloudWatch Alarms. This can be used in conjunction with autoscaling group scaling policies to define a threshold to scale your instances based on metrics such as cpu utilization, application response time, etc.
Instead of using Ansible to configure each EC2 instance, use Ansible to configure an Amazon Machine Image (AMI) to be uploaded and used by your autoscaling group. If your instances are configured identically, configuration is a one and done process. If your instances are configured differently, consider uploading multiple AMIs, and separating into multiple autoscaling groups. You can also use the User Data definition of an EC2 instance to run shell commands on each individual instance at launch (a one time process).
Last, but not least, instead of running this process from &quot;a devops machine&quot;, consider using a build/deploy CI pipeline to run and configure this entire process. Tools such as AWS CodePipeline, Jenkins, GitLab CI, etc. allow for you and other team members to run your configuration in a configured and repeatable manner. It will also allow you define stages and deployment strategies should you choose to implement testing for your application later on in your development process.