terraform-aws-bastion

Create a temporary bastion in an AWS Account

Note

This module automatically looks up the latest AMI each time terraform apply is run. This could result in your bastion EC2 instance being replaced. This shouldn't be a problem. The bastion is intended to be short lived. If this is an issue for you, you probably aren't using the bastion the way it is intended to be used.

Usage

In a clean directory, create a main.tf file that looks like:

provider "aws" {
  version = "~> 5.0"
  region  = "us-west-2"
}

module "bastion" {
  source            = "github.com/byu-oit/terraform-aws-bastion.git?ref=v3.0.0"
  env               = "prd"
  vpc_vpn_to_campus = true
  netid             = "mynetid"
  public_key        = "ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQCwWVPlHpRiXGBmB/VG6PUeJ/Ev+Y39n5PBI4DW3ZMDT1g32nEUjzKtxK6KwVzYFQBhReMO2ry4uSTiNIzuOtHk/OCfcdPc8wbW3RlHBgbqs6p7DfYRJAXJCnWEjovijaVY0lyL4+7/YuprZwBaA2NfUIRN8UwVxZck3ULMnCK6BKog0UAE9NQZ9Z0vAtgLYPo9eVJEuGrxEszN29X+4Fl6u3T8x0XQ9EoMWU4YNwKfzBIof3th9Cbv4+FlEKpOFYuCc5vB2NPotalN8phEUqnvtsDkmCLAop6+MrUlnNNYIzmh2RLeqDF+M/ZnX8xb+V/mT9vARVcdcYCxKYeyXLvT example"
  #ingress_cidrs     = ["128.187.112.21/32"] # optional (defaults to BYU Campus)
  #subnet_type       = private # optional (defaults to public)
}

# When you use a bastion, you almost always need to add a
# security group rule to allow that bastion to connect to
# another resource (RDS, EC2, EFS, etc.). You can do that in
# Terraform, with an aws_security_group_rule resource.
/*
resource "aws_security_group_rule" "bastion_to_rds" {
  type                     = "ingress"
  source_security_group_id = module.bastion.security_group.id

  # Different services (mysql, postgress, SSH, EFS, etc) have
  # different ports. Specify the correct ports here.
  from_port                = 3306
  to_port                  = 3306
  protocol                 = "tcp"

  # You'll need to login to the console and lookup the
  # Security Group ID for the target resource that your
  # bastion is going to connect to.
  security_group_id        = "sg_xxxxxxxxxxxxxx"
}

output "tunnel_connect" {
  # You'll need to login to the console and lookup the
  # Endpoint Address of your RDS instance. If you are
  # targeting something other than mysql on RDS, update the
  # host and ports to match your target resource.
  #
  # Learn more about SSH Tunneling: https://www.ssh.com/ssh/tunneling/example
  value = "ssh -L 3306:my_rds_instance_address:3306 ec2-user@${module.bastion.route53_record.name}"
}
*/

output "connect" {
	value = module.bastion.connect
}

You need to update the variable values. (i.e. use your netid, your public ssh key, etc.)

Then run:

terraform init
terraform apply

When you're done, run:

terraform destroy

Backend

The bastion is really intended to be ephemeral (spin it up, use it, tear it down). So there's no need for a backend.

Input

Name	Type	Description	Default Value
env	string	Environment (for tagging the bastion) (e.g. dev, prd)
vpc_vpn_to_campus	bool	Set to true if the bastion needs to be in the VPC that has VPN access to campus	false
netid	string	Your Net ID (for naming the bastion)
public_key	string	Public SSH Key (e.g. "ssh-rsa AA....Qw== comment").
ingress_cidrs	list(string)	IP Address Ranges that should have access to the bastion.	["128.187.0.0/16", "10.0.0.0/8"]
subnet_type	string	Which subnet type sould the bastion launch in? (e.g. public, private, data)	"public"
site_url	string	The static URL to use as an alias to the bastion host address.	"${var.netid}-bastion.${module.acs.route53_zone.name}"
site_zone_id	string	The ID of the hosted zone to contain the site_url record.	module.acs.route53_zone.zone_id

Notes on subnet_type:

• public is useful for troubleshooting when your target is inside AWS. But the public subnets don't have routing to the VPN, so you won't be able to reach back to campus from the bastion.
• private is useful for troubleshooting connections back to campus across the VPN. But you won't be able to reach the bastion publicly from your workstation.
• If you need a private bastion, you'll either need to reach it across the VPN (i.e. be running the dc vpn on your workstation), or spin up a second "public" bastion to go through.

Output

Name	Type	Description
connect	string	SSH connection details for the bastion
ec2_instance	object	The bastion EC2 Instance
security_group	object	The security group that controls access to the bastion
key_pair	object	The SSH keypair assigned to the bastion
route53_record	object	The Route53 "A" Record to alias the bastion public or private IP address

Resources

• An EC2 Instance (the bastion) in a public subnet
• A Security Group allowing SSH on port 22 from campus
• A keypair using the public key input variable (granting access to the EC2 instance)
• A Route53 entry to alias the bastion public or private ip address