Runtimes and images
Images, sizes, and the two runtimes a host can provide.
Image
An image is the filesystem a Dock starts from. ubuntu-24.04 is the only image
available today: a minimal Ubuntu with systemd, ssh, Docker, git, and curl.
Dock does not ship coding agents. Install whichever you use in your environment
setup script.
Size
A Dock's size is three numbers you pass on create or branch:
| Field | Default | Limit |
|---|---|---|
cpus | 2 | 1 to 64 |
memoryMiB | 4096 | 512 to 262144 |
diskGiB | 20 | 1 to 2048 |
The limits are validation bounds. A host must also have room: with no enrolled
host online, creation fails with 503 no_host_capacity; when hosts are online but none has
room for the requested cpus and memoryMiB, it fails with 503
capacity_exhausted.
Runtime
The runtime is chosen by the host the Dock lands on. It is read-only on the
Dock object, with the paths that survive a stop in persistentPaths.
| Runtime | How it runs | What persists |
|---|---|---|
microvm | Firecracker on Linux KVM | The whole disk |
gvisor | runsc on Linux with Docker | Only /home/user/work |
Use microvm when you need the whole machine kept (installed packages,
system changes). A gvisor Dock restarts from the image with only
/home/user/work restored, so put work there.