Atlantis

A unified workflow for collaborating on Terraform through GitHub

Walkthrough Video

Read about Why We Built Atlantis

• Features
• Getting Started
• Pull Request Commands
• Project Structure
• Environments
• Terraform Versions
• Project-Specific Customization
• Locking
• Approvals
• Production-Ready Deployment
  • Docker
• Server Configuration
• AWS Credentials
• Glossary
  • Project
  • Environment
• FAQ
• Contributing
• Credits

Features

➜ Collaborate on Terraform with your team

• Run terraform plan and apply from GitHub pull requests so everyone can review the output
• Lock environments until pull requests are merged to prevent concurrent modification and confusion

➜ Developers can write Terraform safely

• No need to distribute AWS credentials to your whole team. Developers can submit Terraform changes and run plan and apply directly from the pull request
• Optionally, require a review and approval prior to running apply

➜ Also

• No more copy-pasted code across environments. Atlantis supports using an env/{env}.tfvars file per environment so you can write your base configuration once
• Support multiple versions of Terraform with a simple project config file

Getting Started

Download from https://github.com/hootsuite/atlantis/releases

Run

./atlantis bootstrap

This will walk you through running Atlantis locally. It will

• fork an example terraform project
• install terraform (if not already in your PATH)
• install ngrok so we can expose Atlantis to GitHub
• start Atlantis

If you're ready to permanently set up Atlantis see Production-Ready Deployment

Pull Request Commands

Atlantis currently supports three commands that can be run via pull request comments:

atlantis help

View help

atlantis plan [env]

Runs terraform plan for the changes in this pull request. If [env] is specified, will switch to that environment (or workspace in terraform > 0.10), before running plan. Any additional arguments passed to atlantis plan will be passed on to terraform plan. For example if you'd like to run terraform plan -target={target} then you can comment atlantis plan -target={target}.

atlantis apply [env]

Runs terraform apply for the plan generated by atlantis plan. If [env] is specified, will switch to that env/workspace. Any additional arguments passed to atlantis apply will be passed on to terraform apply.

Project Structure

Atlantis supports several Terraform project structures:

• a single Terraform project at the repo root

.
├── main.tf
└── ...

• multiple project folders in a single repo (monorepo)

.
├── project1
│   ├── main.tf
|   └── ...
└── project2
    ├── main.tf
    └── ...

• one folder per environment

.
├── staging
│   ├── main.tf
|   └── ...
└── production
    ├── main.tf
    └── ...

• using env/{env}.tfvars to define environment specific variables. This works in both multi-project repos and single-project repos.

.
├── env
│   ├── production.tfvars
│   └── staging.tfvars
└── main.tf

or

.
├── project1
│   ├── env
│   │   ├── production.tfvars
│   │   └── staging.tfvars
│   └── main.tf
└── project2
    ├── env
    │   ├── production.tfvars
    │   └── staging.tfvars
    └── main.tf

With the above project structure you can de-duplicate your Terraform code between environments without requiring extensive use of modules. At Hootsuite we've found this project format to be very successful and use it in all of our 100+ Terraform repositories.

Environments

Terraform recently introduced State Environments that

allows a single folder of Terraform configurations to manage multiple distinct infrastructure resources

If you're using a Terraform version >= 0.9.0, Atlantis supports environments through an additional argument to the atlantis plan and atlantis apply commands. For example,

atlantis plan staging

If an environment is specified Atlantis will use terraform env select {env} prior to running terraform plan or terraform apply.

If you're using the env/{env}.tfvars project structure we will also append -tfvars=env/{env}.tfvars to plan and apply.

If no environment is specified we will use default as the environment.

Terraform Versions

By default, Atlantis will use the terraform executable that is in its path. To use a specific version of Terraform just install that version on the server that Atlantis is running on.

If you would like to use a different version of Terraform for some projects but not for others

1. Install the desired version of Terraform into the $PATH of where Atlantis is running and name it terraform{version}, ex. terraform0.8.8.
2. In the project root (which is not necessarily the repo root) of any project that needs a specific version, create an atlantis.yaml file as follows

---
terraform_version: 0.8.8 # set to desired version

So your project structure will look like

.
├── main.tf
└── atlantis.yaml

Now when Atlantis executes it will use the terraform{version} executable.

Project-Specific Customization

An atlantis.yaml config file in your project root (which is not necessarily the repo root) can be used to customize

• what commands Atlantis runs before init, get, plan and apply with pre_init, pre_get, pre_plan and pre_apply
• what commands Atlantis runs after plan and apply with post_plan and post_apply
• additional arguments to be supplied to specific terraform commands with extra_arguments
  • the commmands that we support adding extra args to are init, get, plan and apply
• what version of Terraform to use (see Terraform Versions)

The schema of the atlantis.yaml project config file is

# atlantis.yaml
---
terraform_version: 0.8.8 # optional version
# pre_init commands are run when the Terraform version is >= 0.9.0
pre_init:
  commands:
  - "curl http://example.com"
# pre_get commands are run when the Terraform version is < 0.9.0
pre_get:
  commands:
  - "curl http://example.com"
pre_plan:
  commands:
  - "curl http://example.com"
post_plan:
  commands:
  - "curl http://example.com"
pre_apply:
  commands:
  - "curl http://example.com"
post_apply:
  commands:
  - "curl http://example.com"
extra_arguments:
  - command_name: plan
    arguments:
    - "-tfvars=myvars.tfvars"

When running the pre_plan, post_plan, pre_apply, and post_apply commands the following environment variables are available

• ENVIRONMENT: if an environment argument is supplied to atlantis plan or atlantis apply this will be the value of that argument. Else it will be default
• ATLANTIS_TERRAFORM_VERSION: local version of terraform or the version from terraform_version if specified, ex. 0.10.0
• WORKSPACE: absolute path to the root of the project on disk

Locking

When plan is run, the project and environment are Locked until an apply succeeds and the pull request is merged. This protects against concurrent modifications to the same set of infrastructure and prevents users from seeing a plan that will be invalid if another pull request is merged.

To unlock the project and environment without completing an apply and merging, click the link at the bottom of the plan comment to discard the plan and delete the lock. Once a plan is discarded, you'll need to run plan again prior to running apply.

Approvals

If you'd like to require pull requests to be approved prior to a user running atlantis apply simply run Atlantis with the --require-approval flag. By default, no approval is required.

For more information on pull request reviews and approvals see: https://help.github.com/articles/about-pull-request-reviews/

Production-Ready Deployment

Install Terraform

terraform needs to be in the $PATH for Atlantis. Download from https://www.terraform.io/downloads.html

unzip path/to/terraform_*.zip -d /usr/local/bin

Check that it's in your $PATH

$ terraform version
Terraform v0.10.0

If you want to use a different version of Terraform see Terraform Versions

Hosting Atlantis

Atlantis needs to be hosted somewhere that github.com or your GitHub Enterprise installation can reach. Developers in your organization also need to be able to access Atlantis to view the UI and to delete locks.

By default Atlantis runs on port 4141. This can be changed with the --port flag.

Add GitHub Webhook

Once you've decided where to host Atlantis you can add it as a Webhook to GitHub. If you already have a GitHub organization we recommend installing the webhook at the organization level rather than on each repository, however both methods will work.

If you're not sure if you have a GitHub organization see https://help.github.com/articles/differences-between-user-and-organization-accounts/

If you're installing on the organization, navigate to your organization's page and click Settings. If installing on a single repository, navigate to the repository home page and click Settings.

• Select Webhooks or Hooks in the sidebar
• Click Add webhook
• set Payload URL to http://$URL/events where $URL is where Atlantis is hosted. Be sure to add /events
• set Content type to application/json
• leave Secret blank or set this to a random key (https://www.random.org/strings/). If you set it, you'll need to use the --gh-webhook-secret option when you start Atlantis
• select Let me select individual events
• check the boxes
  • Pull request review
  • Push
  • Issue comment
  • Pull request
• leave Active checked
• click Add webhook

Create a GitHub Token

We recommend creating a new user in GitHub named atlantis that performs all API actions however you can use any user. Once you've created the user (or have decided to use an existing user) you need to create a personal access token.

• follow https://help.github.com/articles/creating-a-personal-access-token-for-the-command-line/#creating-a-token
• copy the access token

Start Atlantis

Now you're ready to start Atlantis! Run

$ atlantis server --atlantis-url $URL --gh-user $USERNAME --gh-token $TOKEN --gh-webhook-secret $SECRET
2049/10/6 00:00:00 [WARN] server: Atlantis started - listening on port 4141

• $URL is the URL that Atlantis can be reached at
• $USERNAME is the GitHub username you generated the token for
• $TOKEN is the access token you created. If you don't want this to be passed in as an argument for security reasons you can specify it in a config file (see Configuration) or as an environment variable: ATLANTIS_GH_TOKEN
• $SECRET is the random key you used for the webhook secret. If you left the secret blank then don't specify this flag. If you don't want this to be passed in as an argument for security reasons you can specify it in a config file (see Configuration) or as an environment variable: ATLANTIS_GH_WEBHOOK_SECRET

Atlantis is now running! We recommend running it under something like Systemd or Supervisord.

Docker

Atlantis also ships inside a docker image with Terraform versions 0.8.8, 0.9.11 and 0.10.0. Run the docker image:

docker run hootsuite/atlantis server --gh-user=GITHUB_USERNAME --gh-token=GITHUB_TOKEN

Usage

If you would like to add things like AWS credential files to the docker image, you can do something like this:

• Create a custom docker file

vim Dockerfile-custom

FROM hootsuite/atlantis

# copy aws credentials
COPY credentials /home/atlantis/.aws/credentials

• Build docker image

docker build -t {YOUR_DOCKER_ORG}/atlantis-custom -f Dockerfile-custom .

• Run docker image

docker run {YOUR_DOCKER_ORG}/atlantis-custom server --gh-user=GITHUB_USERNAME --gh-token=GITHUB_TOKEN

Testing Out Atlantis

If you'd like to test out Atlantis before running it on your own repositories you can fork our example repo.

• Fork https://github.com/hootsuite/atlantis-example
• If you didn't add the Webhook as to your organization add Atlantis as a Webhook to the forked repo (see Add GitHub Webhook)
• Now that Atlantis can receive events you should be able to comment on a pull request to trigger Atlantis. Create a pull request
  • Click Branches on your forked repo's homepage
  • click the New pull request button next to the example branch
  • Change the base to {your-repo}/master
  • click Create pull request
• Now you can test out Atlantis
  • Create a comment atlantis help to see what commands you can run from the pull request
  • atlantis plan will run terraform plan behind the scenes. You should see the output commented back on the pull request. You should also see some logs show up where you're running atlantis server
  • atlantis apply will run terraform apply. Since our pull request creates a null_resource (which does nothing) this is safe to do.

Server Configuration

Atlantis configuration can be specified via command line flags or a YAML config file. The gh-token flag can also be specified via an ATLANTIS_GH_TOKEN environment variable. Config file values are overridden by environment variables which in turn are overridden by flags.

To use a yaml config file, run atlantis with --config /path/to/config.yaml. The keys of your config file should be the same as the flag, ex.

---
gh-token: ...
log-level: ...

To see a list of all flags and their descriptions run atlantis server --help

AWS Credentials

Atlantis simply shells out to terraform so you don't need to do anything special with AWS credentials. As long as terraform works where you're hosting Atlantis, then Atlantis will work. See https://www.terraform.io/docs/providers/aws/#authentication for more detail.

Multiple AWS Accounts

Atlantis supports multiple AWS accounts through the use of Terraform's AWS Authentication.

If you're using the Shared Credentials file you'll need to ensure the server that Atlantis is executing on has the corresponding credentials file.

If you're using Assume role you'll need to ensure that the credentials file has a default profile that is able to assume all required roles.

Environment variables authentication won't work for multiple accounts since Atlantis wouldn't know which environment variables to execute Terraform with.

Assume Role Session Names

Atlantis injects the Terraform variable atlantis_user and sets it to the GitHub username of the user that is running the Atlantis command. This can be used to dynamically name the assume role session. This is used at Hootsuite so AWS API actions can be correlated with a specific user.

To take advantage of this feature, use Terraform's built-in support for assume role and use the atlantis_user terraform variable

provider "aws" {
  assume_role {
    role_arn     = "arn:aws:iam::ACCOUNT_ID:role/ROLE_NAME"
    session_name = "${var.atlantis_user}"
  }
}

# need to define the atlantis_user variable to avoid terraform errors
variable "atlantis_user" {
  default = "atlantis_user"
}

If you're also using the S3 Backend make sure to add the role_arn option:

terraform {
  backend "s3" {
    bucket   = "mybucket"
    key      = "path/to/my/key"
    region   = "us-east-1"
    role_arn = "arn:aws:iam::ACCOUNT_ID:role/ROLE_NAME"
    # can't use var.atlantis_user as the session name because
    # interpolations are not allowed in backend configuration
    # session_name = "${var.atlantis_user}" WON'T WORK
  }
}

Terraform doesn't support interpolations in backend config so you will not be able to use session_name = "${var.atlantis_user}". However, the backend assumed role is only used for state-related API actions. Any other API actions will be performed using the assumed role specified in the aws provider and will have the session named as the GitHub user.

Glossary

Project

A Terraform project. Multiple projects can be in a single GitHub repo. We identify a project by its repo and the path to the root of the project within that repo.

Environment

A Terraform environment. See terraform docs for more information.

FAQ

Q: Does Atlantis affect Terraform remote state?

A: No. Atlantis does not interfere with Terraform remote state in anyway. Under the hood, Atlantis is simply executing terraform plan and terraform apply.

Q: How does Atlantis locking interact with Terraform locking?

A: Atlantis provides locking of pull requests that prevents concurrent modification of the same infrastructure (Terraform project) whereas Terraform locking only prevents two concurrent terraform apply's from happening.

Terraform locking can be used alongside Atlantis locking since Atlantis is simply executing terraform commands.

Q: How to run Atlantis in high availability mode? Does it need to be?

A: Atlantis server can easily be run under the supervision of a init system like upstart or systemd to make sure atlantis server is always running.

Atlantis currently stores all locking and Terraform plans locally on disk under the --data-dir directory (defaults to ~/.atlantis). Because of this there is currently no way to run two or more Atlantis instances concurrently.

However, if you were to lose the data, all you would need to do is run atlantis plan again on the pull requests that are open. If someone tries to run atlantis apply after the data has been lost then they will get an error back, so they will have to re-plan anyway.

Q: How to add SSL to Atlantis server?

A: Atlantis currently only supports HTTP. In order to add SSL you will need to front Atlantis server with NGINX or HAProxy. Follow the document here to use configure NGINX with SSL as a reverse proxy.

Contributing

Want to contribute? Check out CONTRIBUTING.

Credits

• Atlantis Logo: Icon made by freepik from www.flaticon.com