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Configuring prebuilds

You can configure your project to prebuild a codespace automatically each time you push a change to your repository.

People with admin access to a repository can configure prebuilds for the repository.

Codespaces is available for organizations using GitHub Team or GitHub Enterprise Cloud. For more information, see "GitHub's products."

Note: The ability to prebuild codespaces is currently in beta and subject to change.

You can set up a prebuild configuration for a specific branch of your repository.

Any branch created from a prebuild-enabled base branch will typically also get assigned a prebuild during codespace creation. This is true if the dev container on the branch is the same as on the base branch. This is because the majority of the prebuild configuration for branches with the same dev container configuration are identical, so developers can benefit from faster codespace creation times on those branches also. For more information, see "Introduction to dev containers."

Typically, when you configure prebuilds for a branch, prebuilds will be available for Codespaces machine types for that branch. However, if your repository is greater than 32 GB, prebuilds won't be available for 2-core and 4-core machine types, since the storage these provide is limited to 32 GB.

Prebuilds are not available if you choose to use a devcontainer.json file from a .devcontainer/SUBDIRECTORY location when you create a codespace. For information about choosing a devcontainer.json file, see "Creating a codespace."

Prerequisites

Before you can configure prebuilds for your project the following must be true:

Configuring a prebuild

  1. On GitHub.com, navigate to the main page of the repository.

  2. Under your repository name, click Settings. Repository settings button

  3. In the "Code & automation" section of the sidebar, click Codespaces.

  4. Under "Prebuild configuration", click Set up prebuild.

    The 'Set up prebuilds' button

  5. Choose the branch for which you want to set up a prebuild.

    The Branch drop-down menu

    Note: Any branches created from a prebuild-enabled base branch will typically also get prebuilds. For example, if you enable prebuilds for the default branch of the repository, branches based on the default branch will, in most cases, also get prebuilds.

  6. Choose the regions in which you want to set up a prebuild. Developers must be located in a region you select to be able to create codespaces from a prebuild. Alternatively, select All regions.

    The region selection options

    Notes:

    • The prebuild template for each region will incur individual charges. You should, therefore, only enable prebuilds for regions in which you know they'll be used. For more information, see "About Codespaces prebuilds."
    • Developers can set their default region for Codespaces, which can allow you to enable prebuilds for fewer regions. For more information, see "Setting your default region for Codespaces."
  7. Choose how you want to automatically trigger updates of the prebuild template.

    • Every push (the default setting) - With this setting, prebuild configurations will be updated on every push made to the given branch. This will ensure that codespaces generated from a prebuild template always contain the latest codespace configuration, including any recently added or updated dependencies.
    • On configuration change - With this setting, prebuild configurations will be updated every time associated configuration files for a given repo and branch are updated. This ensures that changes to the dev container configuration files for the repository are used when a codespace is generated from a prebuild template. The Actions workflow that updates the prebuild template will run less often, so this option will use fewer Actions minutes. However, this option will not guarantee that codespaces always include recently added or updated dependencies, so these may have to be added or updated manually after a codespace has been created.
    • Scheduled - With this setting, you can have your prebuild configurations update on a custom schedule that's defined by you. This can reduce consumption of Actions minutes, and reduce the amount of time during which prebuilds are unavailable because they are being updated. However, with this option, codespaces may be created that do not use the latest dev container configuration changes.

    The prebuild trigger options

  8. Click Create.

    The prebuild configuration is listed on the Codespaces page of your repository settings. A GitHub Actions workflow is queued and then run to create prebuild templates, based on the branch you selected, in the regions you specified.

    Note: By default, the GitHub Actions workflow for a prebuild configuration can only access resources in its own repository. If your project uses resources from outside of the repository, you'll need to set the CODESPACES_PREBUILD_TOKEN secret to grant the required access. For more information, see "Allowing a prebuild to access external resources."

Configuring access to resources that are not in the repository

By default, the GitHub Actions workflow for a prebuild configuration can only access its own repository contents. If your project needs to access external resources to build the development environment, you will need to set up a personal access token (PAT) with the appropriate access scopes.

For more information, see “Allowing a prebuild to access external resources."

Configuring environment variables

To allow the prebuild process to access environment variables required to create your development environment, you can set these either as Codespaces repository secrets or as Codespaces organization secrets. For more information, see "Adding secrets for a repository" and "Adding secrets for an organization."

Prebuilds do not use any user-level secrets while building your environment, because these are not added until after the codespace has been created.

Codespaces secrets that you create in this way will be accessible by anyone who creates a codespace from this repository. If you do not want this, you can alternatively set the CODESPACES_PREBUILD_TOKEN secret. The CODESPACES_PREBUILD_TOKEN secret is only used for prebuilding and its value is not accessible in users' codespaces. For more information, see “Allowing a prebuild to access external resources."

Configuring time-consuming tasks to be included in the prebuild

You can use the onCreateCommand and updateContentCommand commands in your devcontainer.json to include time-consuming processes as part of the prebuild template creation. For more information, see the Visual Studio Code documentation, "devcontainer.json reference."

onCreateCommand is run only once, when the prebuild template is created, whereas updateContentCommand is run at template creation and at subsequent template updates. Incremental builds should be included in updateContentCommand since they represent the source of your project and need to be included for every prebuild template update.

Further reading