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