Setting up a local development environment

Required software

To develop Ferrocene locally, you’ll need to have the following software installed:

  • git, as the version control system used by Ferrocene.

  • Python 3, needed for the entry point of Rust’s build system.

  • AWS CLI v2, version 2.9.0 or greater, needed to interact with our AWS account. Note that most Linux distributions only include version 1 of the AWS CLI, while we explicitly require version 2.

Configuring git

You need to have an SSH key registered in your GitHub account to be able to clone the Ferrocene repository. You can check out GitHub’s documentation if you don’t already have an SSH key configured in your account and your local machine. If you need to generate a new key as part of the process, please follow GitHub’s recommendations to generate a secure key.

Once the SSH key is registered in your GitHub account, you need to authorize it for the Ferrocene organization using your SSO session. To do so, visit the SSH and GPG keys page of the GitHub settings, and next to the key you use on your work device click “Configure SSO”. Finally, click “Authorize” next to “ferrocene” and follow the prompt to enable the SSH key to access repositories in the Ferrocene organization.


Add SSH key to GitHub profile

Configuring AWS CLI

To authorize the AWS CLI to access our AWS resources, you need to add the following snippet to the ~/.aws/config file in your work device:

[profile ferrocene-ci]
sso_session = ferrous-systems
sso_account_id = 886866542769
sso_role_name = FerroceneDeveloper
region = us-east-1

[sso-session ferrous-systems]
sso_start_url =
sso_region = eu-central-1


If you do not already have the ~/.aws/config file in your local system, create a blank one.

If you already have the [sso-session ferrous-systems] block in your ~/.aws/config you do not need to add it again, as only one copy of it is required.

Once that’s done, you can log into the CLI with the following command:

aws sso login --profile ferrocene-ci

This will open your browser (if that doesn’t happen, click the link displayed by the command). Authenticate with SSO on that page (if prompted) and click “Approve”:


AWS SSO log in prompt


You will need to authenticate with AWS SSO every week. The Ferrocene build system will remind you to authenticate if you’re trying to perform actions that require AWS access but you didn’t log in that week.

Cloning the Ferrocene repository

To clone the Ferrocene repository, you can run this command:

git clone

This will take a while to complete (as it is downloading the whole history), and will create a ferrocene/ directory inside the current directory.

Configuring the Ferrocene build system

The Ferrocene build system requires a configuration file to be present at the root of the repository, in a file named config.toml. You should put this content in it:

profile = "compiler"
change-id = 102579

aws-profile = "ferrocene-ci"
test-outcomes = "download-ci"

lld = true

There are a lot of other options available: you can look at the documentation for all of them in the config.toml.example file for further details.