Highly Available Bastion Host in AWS implemented with Terraform

A module to create a HA Bastion Host on AWS which runs in an Autoscaling Group (ASG).

INPUT

region:                     AWS region in which the Bastion should be deployed
project:                    Name of the project these resources are being created in
environment:                dev, test, production, etc
instance_type:              Instance type of the Bastion host
max_size:                   Max number of bastion instances running simultaneously
min_size:                   Min number of bastion instances running simultaneously
desired_capacity:           The desired number of bastion instances that should be running at any time
health_check_grace_period:  Time (seconds) to wait after instance launches before health-checking
cooldown_period:            Time (seconds) to wait before another scaling activity can start
public_ssh_key:             Public half of SSH key
security_group_ids:         List of security groups to apply to the instances
subnet_ids:                 A list of all the subnet IDs for the Autoscaling Group to launch the Bastion across
volume_type:                Root volume type
volume_size:                Root volume size (GB)
dns_zone_id:                DNS hosted zone from Route53
ttl:                        DNS cache time to live (seconds)