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AWS Bastion Terraform module

Open Source Helpers

Terraform module which creates a secure SSH bastion on AWS.

Mainly inspired by Securely Connect to Linux Instances Running in a Private Amazon VPC

Features

This module will create an SSH bastion to securely connect in SSH to your private instances. Bastion Infrastrucutre All SSH commands are logged on an S3 bucket for security compliance, in the /logs path.

SSH users are managed by their public key, simply drop the SSH key of the user in the /public-keys path of the bucket. Keys should be named like 'username.pub', this will create the user 'username' on the bastion server. Username must contain alphanumeric characters only.

Then after you'll be able to connect to the server with :

ssh [-i path_to_the_private_key] username@bastion-dns-name

From this bastion server, you'll able to connect to all instances on the private subnet.

If there is a missing feature or a bug - open an issue.

Usage

module "bastion" {
  source = "Guimove/bastion/aws"
  bucket_name = "my_famous_bucket_name"
  region = "eu-west-1"
  vpc_id = "my_vpc_id"
  is_lb_private = "true|false"
  bastion_host_key_pair = "my_key_pair"
  create_dns_record = "true|false"
  hosted_zone_id = "my.hosted.zone.name."
  bastion_record_name = "bastion.my.hosted.zone.name."
  bastion_iam_policy_name = "myBastionHostPolicy"
  elb_subnets = [
    "subnet-id1a",
    "subnet-id1b"
  ]
  auto_scaling_group_subnets = [
    "subnet-id1a",
    "subnet-id1b"
  ]
  tags = {
    "name" = "my_bastion_name",
    "description" = "my_bastion_description"
  }
}

Requirements

Name Version
terraform ~> 1.0
aws ~> 4.0

Providers

Name Version
aws ~> 4.0

Modules

No modules.

Resources

Name Type
aws_autoscaling_group.bastion_auto_scaling_group resource
aws_iam_instance_profile.bastion_host_profile resource
aws_iam_policy.bastion_host_policy resource
aws_iam_role.bastion_host_role resource
aws_iam_role_policy_attachment.bastion_host resource
aws_kms_alias.alias resource
aws_kms_key.key resource
aws_launch_template.bastion_launch_template resource
aws_lb.bastion_lb resource
aws_lb_listener.bastion_lb_listener_22 resource
aws_lb_target_group.bastion_lb_target_group resource
aws_route53_record.bastion_record_name resource
aws_s3_bucket.bucket resource
aws_s3_bucket_acl.bucket resource
aws_s3_bucket_lifecycle_configuration.bucket resource
aws_s3_bucket_ownership_controls.bucket-acl-ownership resource
aws_s3_bucket_server_side_encryption_configuration.bucket resource
aws_s3_bucket_versioning.bucket resource
aws_s3_object.bucket_public_keys_readme resource
aws_security_group.bastion_host_security_group resource
aws_security_group.private_instances_security_group resource
aws_security_group_rule.egress_bastion resource
aws_security_group_rule.ingress_bastion resource
aws_security_group_rule.ingress_instances resource
aws_ami.amazon-linux-2 data source
aws_iam_policy_document.assume_policy_document data source
aws_iam_policy_document.bastion_host_policy_document data source
aws_kms_alias.kms-ebs data source
aws_subnet.subnets data source

Inputs

Name Description Type Default Required
allow_ssh_commands Allows the SSH user to execute one-off commands. Pass true to enable. Warning: These commands are not logged and increase the vulnerability of the system. Use at your own discretion. bool false no
associate_public_ip_address n/a bool true no
auto_scaling_group_subnets List of subnets where the Auto Scaling Group will deploy the instances list(string) n/a yes
bastion_additional_security_groups List of additional security groups to attach to the launch template list(string) [] no
bastion_ami The AMI that the Bastion Host will use. string "" no
bastion_host_key_pair Select the key pair to use to launch the bastion host string n/a yes
bastion_iam_permissions_boundary IAM Role Permissions Boundary to constrain the bastion host role string "" no
bastion_iam_policy_name IAM policy name to create for granting the instance role access to the bucket string "BastionHost" no
bastion_iam_role_name IAM role name to create string null no
bastion_instance_count n/a number 1 no
bastion_launch_template_name Bastion Launch template Name, will also be used for the ASG string "bastion-lt" no
bastion_record_name DNS record name to use for the bastion string "" no
bastion_security_group_id Custom security group to use string "" no
bucket_force_destroy The bucket and all objects should be destroyed when using true bool false no
bucket_name Bucket name where the bastion will store the logs string n/a yes
bucket_versioning Enable bucket versioning or not bool true no
cidrs List of CIDRs that can access the bastion. Default: 0.0.0.0/0 list(string)
[
"0.0.0.0/0"
]
no
create_dns_record Choose if you want to create a record name for the bastion (LB). If true, 'hosted_zone_id' and 'bastion_record_name' are mandatory bool n/a yes
create_elb Choose if you want to deploy an ELB for accessing bastion hosts. Only select false if there is no need to SSH into bastion from outside. If true, you must set elb_subnets and is_lb_private bool true no
disk_encrypt Instance EBS encryption bool true no
disk_size Root EBS size in GB number 8 no
elb_subnets List of subnets where the ELB will be deployed list(string) [] no
enable_http_protocol_ipv6 Enables or disables the IPv6 endpoint for the instance metadata service bool false no
enable_instance_metadata_tags Enables or disables access to instance tags from the instance metadata service bool false no
enable_logs_s3_sync Enable cron job to copy logs to S3 bool true no
extra_user_data_content Additional scripting to pass to the bastion host. For example, this can include installing PostgreSQL for the psql command. string "" no
hosted_zone_id Name of the hosted zone where we'll register the bastion DNS name string "" no
http_endpoint Whether the metadata service is available bool true no
http_put_response_hop_limit The desired HTTP PUT response hop limit for instance metadata requests number 1 no
instance_type Instance size of the bastion string "t3.nano" no
ipv6_cidrs List of IPv6 CIDRs that can access the bastion. Default: ::/0 list(string)
[
"::/0"
]
no
is_lb_private If TRUE, the load balancer scheme will be "internal" else "internet-facing" bool null no
kms_enable_key_rotation Enable key rotation for the KMS key bool false no
log_auto_clean Enable or disable the lifecycle bool false no
log_expiry_days Number of days before logs expiration number 90 no
log_glacier_days Number of days before moving logs to Glacier number 60 no
log_standard_ia_days Number of days before moving logs to IA Storage number 30 no
private_ssh_port Set the SSH port to use between the bastion and private instance number 22 no
public_ssh_port Set the SSH port to use from desktop to the bastion number 22 no
region n/a string n/a yes
tags A mapping of tags to assign map(string) {} no
use_imds_v2 Use (IMDSv2) Instance Metadata Service V2 bool false no
vpc_id VPC ID where we'll deploy the bastion string n/a yes

Outputs

Name Description
bastion_auto_scaling_group_name The name of the Auto Scaling Group for bastion hosts
bastion_elb_id The ID of the ELB for bastion hosts
bastion_host_security_group The ID of the bastion host security group
bucket_arn The ARN of the S3 bucket
bucket_kms_key_alias The name of the KMS key alias for the bucket
bucket_kms_key_arn The ARN of the KMS key for the bucket
bucket_name The ID of the S3 bucket
elb_arn The ARN of the ELB for bastion hosts
elb_ip The DNS name of the ELB for bastion hosts
private_instances_security_group The ID of the security group for private instances
target_group_arn The ARN of the target group for the ELB

Known issues

Tags are not applied to the instances generated by the auto scaling group do to known terraform issue : hashicorp/terraform-provider-aws#290

Change of disk encryption isn't propagate immediately. Change have to trigger manually from AWS CLI: Auto Scaling Groups -> Instance refresh . Keep in mind all data from instance will be lost in case there are temporary or custom data.

Authors

Module managed by Guimove.

License

Apache 2 Licensed. See LICENSE for full details.

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Terraform module which creates SSH bastion infrastructure on AWS

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