A Terraform module for creating resilient bastion host using auto-scaling group (min=max=desired=1) and populate its ~/.ssh/authorized_keys with public keys fetched from S3 bucket.

This module can append public keys, setup cron to update them and run additional commands at the end of setup. Note that if it is set up to update the keys, removing a key from the bucket will also remove it from the bastion host.

Only SSH access is allowed to the bastion host.

For Terraform 0.12, use the version from master:

source  = "github.com/terraform-community-modules/tf_aws_bastion_s3_keys"

For Terraform 0.11, pin the module version to match v1.*. For e.g.:

source  = "github.com/terraform-community-modules/tf_aws_bastion_s3_keys?ref=v1.10.0"

Basic example - In your terraform code add something like this:

module "bastion" {
  source                      = "github.com/terraform-community-modules/tf_aws_bastion_s3_keys"
  instance_type               = "t2.micro"
  ami                         = "ami-123456"
  region                      = "eu-west-1"
  iam_instance_profile        = "s3_readonly"
  s3_bucket_name              = "public-keys-demo-bucket"
  vpc_id                      = "vpc-123456"
  subnet_ids                  = ["subnet-123456", "subnet-6789123", "subnet-321321"]
  keys_update_frequency       = "5,20,35,50 * * * *"
  additional_user_data_script = "date"
}

If you want to assign EIP to instance launched by an auto-scaling group you can provide the desired eip as module input and then execute additional_user_data_script which sets EIP. This way you can use Route53 with EIP, which will always point to existing bastion instance. You will also need to add ec2:AssociateAddress permission to iam_instance_profile (see samples/iam_allow_associateaddress.tf):

module "bastion" {
  // see above
  eip = "${aws_eip.bastion.public_ip}"
  iam_instance_profile        = "s3_readonly-allow_associateaddress"
  additional_user_data_script = <<EOF
REGION=$(curl -s http://169.254.169.254/latest/dynamic/instance-identity/document | grep region | awk -F\" '{print $4}')
INSTANCE_ID=$(curl -s http://169.254.169.254/latest/meta-data/instance-id)
aws ec2 associate-address --region $REGION --instance-id $INSTANCE_ID --allocation-id ${aws_eip.bastion.id}
EOF
}

resource "aws_eip" "bastion" {
  vpc = true
}

resource "aws_route53_record" "bastion" {
  zone_id = "..."
  name    = "bastion.example.com"
  type    = "A"
  ttl     = "3600"
  records = [aws_eip.bastion.public_ip]
}

After you run terraform apply you should be able to login to your bastion host like:

$ ssh ${module.bastion.ssh_user}@${aws_eip.bastion.public_ip}

or even like this:

$ ssh [email protected]

PS: In some cases you may consider adding flag -A to ssh command to enable forwarding of the authentication agent connection.

Created and maintained by Anton Babenko.

Apache 2 Licensed. See LICENSE for full details.