Prebuilding your codespaces allows you to be more productive and access your codespace faster, particularly if your repository is large or complex and new codespaces currently take more than 2 minutes to start. This is because any source code, editor extensions, project dependencies, commands, and configurations have already been downloaded, installed, and applied before you create a codespace for your project. Think of a prebuild as a "ready-to-go" template for a codespace.
By default, whenever you push changes to your repository, Codespaces uses GitHub Actions to automatically update your prebuilds.
When prebuilds are available for a particular branch of a repository, and for your region, you'll see the " Prebuild ready" label in the list of machine type options when you create a codespace. If a prebuild is still being created, you will see the " Prebuild in progress" label. For more information, see "Creating a codespace."
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."
By default, a GitHub Actions workflow is triggered every time you create or update a prebuild template, or push to a prebuild-enabled branch. As with other workflows, while prebuild workflows are running they will either consume some of the Actions minutes included with your account, if you have any, or they will incur charges for Actions minutes. For more information about pricing for Actions minutes, see "About billing for GitHub Actions."
Alongside GitHub Actions minutes, you will also be billed for the storage of prebuild templates associated with each prebuild configuration for a given repository and region. Storage of prebuild templates is billed at the same rate as storage of codespaces. For more information, see "Calculating storage usage."
To reduce consumption of Actions minutes, you can set a prebuild template to be updated only when you make a change to your dev container configuration files, or only on a custom schedule. You can also manage your storage usage by adjusting the number of template versions to be retained for your prebuild configurations. For more information, see "Configuring prebuilds."
If you are an organization owner, you can track usage of prebuild workflows and storage by downloading a GitHub Actions usage report for your organization. You can identify workflow runs for prebuilds by filtering the CSV output to only include the workflow called "Create Codespaces Prebuilds." For more information, see "Viewing your GitHub Actions usage." For details of Codespaces storage pricing, see "About billing for Codespaces."
Use of codespaces created using prebuilds is charged at the same rate as regular codespaces.
By default, each push to a branch that has a prebuild configuration results in a GitHub-managed Actions workflow run to update the prebuild template. The prebuild workflow has a concurrency limit of one workflow run at a time for a given prebuild configuration, unless changes were made that affect the dev container configuration for the associated repository. For more information, see "Introduction to dev containers." If a run is already in progress, the workflow run that was queued most recently queued will run next, after the current run completes.
With the prebuild template set to be updated on each push, it means that if there are very frequent pushes to your repository, prebuild template updates will occur at least as often as it takes to run the prebuild workflow. That is, if your workflow run typically takes one hour to complete, prebuilds will be created for your repository roughly hourly, if the run succeeds, or more often if there were pushes that change the dev container configuration on the branch.
For example, let's imagine 5 pushes are made, in quick succession, against a branch that has a prebuild configuration. In this situation:
A workflow run is started for the first push, to update the prebuild template.
If the 4 remaining pushes do not affect the dev container configuration, the workflow runs for these are queued in a "pending" state.
If any of the remaining 4 pushes change the dev container configuration, then the service will not skip that one and will immediately run the prebuild creation workflow, updating the prebuild accordingly if it succeeds.
Once the first run completes, workflow runs for pushes 2, 3, and 4 will be canceled, and the last queued workflow (for push 5) will run and update the prebuild template.