AWS Terraform module which runs Atlantis on AWS Fargate

Atlantis is tool which provides unified workflow for collaborating on Terraform through GitHub, GitLab and Bitbucket Cloud.

This repository contains Terraform infrastructure code which creates AWS resources required to run Atlantis on AWS, including:

• Virtual Private Cloud (VPC)
• SSL certificate using Amazon Certificate Manager (ACM)
• Application Load Balancer (ALB)
• Domain name using AWS Route53 which points to ALB
• AWS Elastic Cloud Service (ECS) and AWS Fargate running Atlantis Docker image
• AWS Parameter Store to keep secrets and access them in ECS task natively

AWS Fargate with optional support for Fargate Spot is used to reduce the bill, and it is also a cool AWS service.

Depending on which SCM system you use, Github repositories or Gitlab projects has to be configured to post events to Atlantis webhook URL.

See README.md in examples for Github or Gitlab for complete details.

Before using Atlantis and the code in this repository please make sure that you have read and understood the security implications described in the official Atlantis documentation.

How to use this?

As often with the code published in terraform-aws-modules GitHub organization you should have everything to run this code and get Atlantis up and running.

There are three ways to do this:

1. As a standalone project
2. As a Terraform module
3. As a part of an existing AWS infrastructure

Run Atlantis as a standalone project

1. Clone this github repository:

$ git clone [email protected]:terraform-aws-modules/terraform-aws-atlantis.git
$ cd terraform-aws-atlantis

2. Copy sample terraform.tfvars.sample into terraform.tfvars and specify required variables there.

3. Run terraform init to download required providers and modules.

4. Run terraform apply to apply the Terraform configuration and create required infrastructure.

5. Run terraform output atlantis_url to get URL where Atlantis is publicly reachable. (Note: It may take a minute or two to get it reachable for the first time)

6. Github webhook is automatically created if github_token, github_organization and github_repo_names were specified. Read Add GitHub Webhook in the official Atlantis documentation or check example "GitHub repository webhook for Atlantis" to add more webhooks.

Run Atlantis as a Terraform module

This way allows integration with your existing Terraform configurations.

module "atlantis" {
  source  = "terraform-aws-modules/atlantis/aws"
  version = "~> 2.0"

  name = "atlantis"

  # VPC
  cidr            = "10.20.0.0/16"
  azs             = ["eu-west-1a", "eu-west-1b", "eu-west-1c"]
  private_subnets = ["10.20.1.0/24", "10.20.2.0/24", "10.20.3.0/24"]
  public_subnets  = ["10.20.101.0/24", "10.20.102.0/24", "10.20.103.0/24"]

  # DNS (without trailing dot)
  route53_zone_name = "example.com"

  # ACM (SSL certificate) - Specify ARN of an existing certificate or new one will be created and validated using Route53 DNS
  certificate_arn = "arn:aws:acm:eu-west-1:135367859851:certificate/70e008e1-c0e1-4c7e-9670-7bb5bd4f5a84"

  # Atlantis
  atlantis_github_user       = "atlantis-bot"
  atlantis_github_user_token = "examplegithubtoken"
  atlantis_repo_whitelist    = ["github.com/terraform-aws-modules/*"]
}

Run Atlantis as a part of an existing AWS infrastructure (use existing VPC)

This way allows integration with your existing AWS resources - VPC, public and private subnets. Specify the following arguments (see methods described above):

vpc_id             = "vpc-1651acf1"
private_subnet_ids = ["subnet-1fe3d837", "subnet-129d66ab"]
public_subnet_ids  = ["subnet-1211eef5", "subnet-163466ab"]

If vpc_id is specified it will take precedence over cidr and existing VPC will be used. private_subnet_ids and public_subnet_ids must be specified also.

Make sure that both private and public subnets were created in the same set of availability zones (ALB will be created in public subnets, ECS Fargate service in private subnets).

If all provided subnets are public (no NAT gateway) then ecs_service_assign_public_ip should be set to true.

Secure Atlantis with ALB Built-in Authentication

OpenID Connect (OIDC)

You can use service like Auth0 to secure access to Atlantis and require authentication on ALB. To enable this, you need to create Auth0 application and provide correct arguments to Atlantis module. Make sure to update application hostname, client id and client secret:

Read more in this post.

Auth0

alb_authenticate_oidc = {
  issuer                              = "https://youruser.eu.auth0.com/"
  token_endpoint                      = "https://youruser.eu.auth0.com/oauth/token"
  user_info_endpoint                  = "https://youruser.eu.auth0.com/userinfo"
  authorization_endpoint              = "https://youruser.eu.auth0.com/authorize"
  authentication_request_extra_params = {}
  client_id                           = "clientid"
  client_secret                       = "secret123" # a data source would be good here
}

Okta

alb_authenticate_oidc = {
  issuer                              = "https://dev-42069.okta.com/"
  token_endpoint                      = "https://dev-42069.okta.com/oauth2/v1/token"
  user_info_endpoint                  = "https://dev-42069.okta.com/oauth2/v1/userinfo"
  authorization_endpoint              = "https://dev-42069.okta.com/oauth2/v1/authorize"
  authentication_request_extra_params = {}
  client_id                           = "clientid"
  client_secret                       = "secret123" # a data source would be good here
}

Read more in this post

AWS Cognito with SAML

The AWS Cognito service allows you to define SAML applications tied to an identity provider (e.g., GSuite). The Atlantis ALB can then be configured to require an authenticated user managed by your identity provider.

To configure AWS Cognito connecting to a GSuite SAML application, you can use the gsuite-saml-cognito Terraform module.

To enable Cognito authentication on the Atlantis ALB, specify the following arguments containing attributes from your Cognito configuration.

alb_authenticate_cognito = {
  user_pool_arn       = "arn:aws:cognito-idp:us-west-2:1234567890:userpool/us-west-2_aBcDeFG"
  user_pool_client_id = "clientid123"
  user_pool_domain    = "sso.your-corp.com"
}

Allow GitHub Webhooks Unauthenticated Access

If you are using one of the authentication methods above along with managed GitHub (not self-hosted enterprise version), you'll need to allow unauthenticated access to GitHub's Webhook static IPs:

allow_unauthenticated_access = true
allow_github_webhooks        = true

Notes

1. AWS Route53 zone is not created by this module, so zone specified as a value in route53_zone_name should be created before using this module. Check documentation for aws_route53_zone.
2. Currently this module configures Atlantis in a way that it can not be used to work with GitHub and Gitlab simultaneously (can't make list of ECS secrets conditionally).
3. For Bitbucket Cloud webhook configuration follow instructions in the official Atlantis documentation.

Examples

• Complete Atlantis with GitHub webhook
• GitHub repository webhook for Atlantis
• GitLab repository webhook for Atlantis

Requirements

Providers

Modules

Resources

Inputs

[
  "0.0.0.0/0"
]

list(object({
    containerName = string
    condition     = string
  }))

list(object(
    {
      name      = string
      valueFrom = string
    }
  ))

list(object(
    {
      name  = string
      value = string
    }
  ))

object({
    type    = string
    options = map(string)
  })

[
  "140.82.112.0/20",
  "185.199.108.0/22",
  "192.30.252.0/22"
]

[
  "arn:aws:iam::aws:policy/service-role/AmazonECSTaskExecutionRolePolicy"
]

list(object({
    name      = string
    hardLimit = number
    softLimit = number
  }))

list(object({
    sourceContainer = string
    readOnly        = bool
  }))

Outputs

Authors

Module is created and maintained by Anton Babenko.

Seth Vargo has created atlantis-on-gke(Terraform configurations for running Atlantis on Google Kubernetes Engine). This inspired me to do similar stuff for AWS Fargate.

License

Apache 2 Licensed. See LICENSE for full details.