Terraform AWS Private Endpoints

The diagram above is a high level representation of the module and the resources it creates; note in this design we DO NOT create an inbound resolver, as its not technically required

Description

The following module provides a AWS recommended pattern for sharing private endpoint services across multiple VPCs, interconnected via a transit gateway. The intent is to retain as much of the traffic directed to AWS services, private and off the internet. Used in combination with the terraform-aws-connectivity.

How it works

• A shared vpc called var.name is created and attached to the transit gateway. Note, this module does not perform any actions on the transit gateway, it is assumed the correct settings to enable connectivity between the var.name vpc and the spokes is in place.
• Inside the shared vpc the private endpoints are created, one for each service defined in var.endpoints. The default security groups permits all https traffic from 10.0.0.0/8 to ingress.
• Optionally, depending on the configuration of the module, a outbound resolver is created. The outbound resolver is used to resolve the AWS services, against the default VPC resolver (VPC+2 ip)
• Route53 resolver rules are created for each of the shared private endpoints, allowing the consumer to pick and choose which endpoints they want to resolve to the shared vpc.
• The endpoints are shared using AWS RAM to the all the principals defined in the var.sharing.principals list e.g. a collection of organizational units.
• The spoke vpc's are responsible for associating the resolver rules with their vpc.
• These rules intercept the DNS queries and route them to the shared vpc resolvers, returning the private endpoint ip address located within them.
• Traffic from the spoke to the endpoints once resolved, is routed via the transit gateway.

AWS References

• AWS PrivateLink
• Shared Private Endpoints

Usage

## Provision the endpoints and resolvers
module "endpoints" {
  source = "../.."

  name = "endpoints"
  tags = var.tags
  endpoints = {
    "s3" = {
      service = "s3"
    },
    "ec2" = {
      service = "ec2"
    },
    "ec2messages" = {
      service = "ec2messages"
    },
    "ssm" = {
      service = "ssm"
    },
    "ssmmessages" = {
      service = "ssmmessages"
    },
    "logs" = {
      service = "logs"
    },
    "kms" = {
      service = "kms"
    },
    "secretsmanager" = {
      service = "secretsmanager"
    }
  }

  sharing = {
    principals = values(var.ram_principals)
  }

  resolvers = {
    outbound = {
      create            = true
      ip_address_offset = 12
    }
  }

  network = {
    # Name of the network to create
    name = "endpoints"
    # Number of availability zones to create subnets in
    private_netmask = 24
    # The transit gateway to connect
    transit_gateway_id = var.transit_gateway_id
    # The cider range to use for the VPC
    vpc_cidr = "10.20.0.0/21"
  }
}

Reuse Existing Network

In order to reuse and existing network (vpc), we need to pass the vpc_id and the subnets ids where the outbound resolver will be provisioned (assuming you are not reusing an existing resolver as well).

## Provision the endpoints and resolvers
module "endpoints" {
  source = "../.."

  name = "endpoints"
  tags = var.tags
  endpoints = {
    "ec2" = {
      service = "ec2"
    },
    "ec2messages" = {
      service = "ec2messages"
    },
    "ssm" = {
      service = "ssm"
    },
    "ssmmessages" = {
      service = "ssmmessages"
    },
  }

  sharing = {
    principals = values(var.ram_principals)
  }

  resolvers = {
    outbound = {
      create            = true
      ip_address_offset = 10
    }
  }

  network = {
    ## The vpc_cidr of the network we are reusing
    vpc_cidr = <VPC_CIDR>
    ## Reuse the network we created above
    vpc_id = <VPC_ID>
    ## Reuse the private subnets we created above i.e subnet-id => cidr
    private_subnet_cidrs_by_id = module.network.private_subnet_cidrs_by_id
    ## Do not create a new network
    create = false
  }
}

Update Documentation

The terraform-docs utility is used to generate this README. Follow the below steps to update:

1. Make changes to the .terraform-docs.yml file
2. Fetch the terraform-docs binary (https://terraform-docs.io/user-guide/installation/)
3. Run terraform-docs markdown table --output-file ${PWD}/README.md --output-mode inject .

Providers

Name	Version
aws	>= 5.0.0

Inputs

Name	Description	Type	Default	Required
name	The name of the environment	string	n/a	yes
network	The network to use for the endpoints and optinal resolvers	object({ availability_zones = optional(number, 2) # Whether to use ipam when creating the network create = optional(bool, true) # Indicates if we should create a new network or reuse an existing one enable_default_route_table_association = optional(bool, true) # Whether to associate the default route table enable_default_route_table_propagation = optional(bool, true) # Whether to propagate the default route table ipam_pool_id = optional(string, null) # The id of the ipam pool to use when creating the network private_netmask = optional(number, 24) # The subnet mask for private subnets, when creating the network i.e subnet-id => 10.90.0.0/24 private_subnet_cidr_by_id = optional(map(string), {}) # The ids of the private subnets to if we are reusing an existing network transit_gateway_id = optional(string, "") ## The transit gateway id to use for the network vpc_cidr = optional(string, "") # The cidrws range to use for the VPC, when creating the network vpc_id = optional(string, "") # The vpc id to use when reusing an existing network vpc_netmask = optional(number, null) # When using ipam this the netmask to use for the VPC vpc_dns_resolver = optional(string, "") # The ip address to use for the vpc dns resolver })	n/a	yes
region	The region to deploy the resources	string	n/a	yes
resolvers	The resolvers to provision	object({ # Indicates we create a single resolver rule, rather than one per service_type create_single_resolver_rule = optional(bool, false) # The configuration for the outbound resolver outbound = object({ # Whether to create the resolver create = optional(bool, true) # If creating the outbound resolver, the address offset to use i.e if 10.100.0.0/24, offset 10, ip address would be 10.100.0.10 ip_address_offset = optional(number, 10) # The protocols to use for the resolver protocols = optional(list(string), ["Do53", "DoH"]) # When not creating the resolver, this is the name of the resolver to use use_existing = optional(string, null) }) })	n/a	yes
tags	The tags to apply to the resources	map(string)	n/a	yes
endpoints	The private endpoints to provision within the shared vpc	map(object({ # Whether to enable private dns private_dns_enabled = optional(bool, true) # The route table ids to use for the endpoint, assuming a gateway endpoint route_table_ids = optional(list(string), null) # service_type of the endpoint i.e. Gateway, Interface service_type = optional(string, "Interface") # The security group ids to use for the endpoint, else create on the fly security_group_ids = optional(list(string), null) # The AWS service we are creating a endpoint for service = string # The IAM policy associated to the endpoint policy = optional(string, null) }))	{ "ec2": { "service": "ec2" }, "ec2messages": { "service": "ec2messages" }, "ssm": { "service": "ssm" }, "ssmmessages": { "service": "ssmmessages" } }	no
sharing	The configuration for sharing the resolvers to other accounts	object({ ## The principals to share the resolvers with principals = optional(list(string), null) # The preifx to use for the shared resolvers share_prefix = optional(string, "resolvers") })	{ "principals": [] }	no

Outputs

Name	Description
endpoints	Array containing the full resource object and attributes for all endpoints created
outbound_resolver_endpoint_id	The id of the outbound resolver if we created one
outbound_resolver_ip_addresses	The ip addresses of the outbound resolver if we created one
private_subnet_attributes_by_az	The attributes of the private subnets
resolver_security_group_id	The id of the security group we created for the endpoints if we created one
rt_attributes_by_type_by_az	The attributes of the route tables
transit_gateway_attachment_id	The id of the transit gateway we used to provision the endpoints
vpc_attributes	The attributes of the vpc we created
vpc_id	The id of the vpc we used to provision the endpoints