Templates

What is a Template?

A template defines the base environment for a sandbox. It specifies the operating system, installed packages, runtime configuration, and resource allocation. When you create a sandbox, you choose a template -- and the sandbox starts with that environment ready to go.

Under the hood, templates are built from Dockerfiles. The build process converts your Dockerfile into a root filesystem image that Firecracker boots as a microVM.

How Templates Work

Dockerfile
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Template Build (async)
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Root Filesystem Image
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Firecracker microVM (sandbox)

1. You submit a Dockerfile (or use a pre-built template).
2. The build system processes the Dockerfile asynchronously via NATS.
3. The resulting root filesystem image is stored and ready for sandbox creation.
4. When you create a sandbox from a template, the image is loaded into a new Firecracker microVM.

Template Resources

Each template defines the resource allocation for its sandboxes:

Resources are set at the template level. All sandboxes created from a template share the same resource allocation.

Pre-built vs Custom Templates

Lelantos provides six pre-built templates that cover common development environments. These are ready to use immediately -- no build step required.

For specialized workloads, you can build custom templates from any Dockerfile. Custom templates support the same resource configuration and go through an asynchronous build process.