roc on a unikernel · show and tell

I mentioned during the call yesterday that I have a Roc app running on a unikernel.

I also have my dog-park repo running on bare metal at https://dogpark.lynrummy.com/dogpark, but it's not a great example, since 95% of the app is client-side, so it's just Roc running in your browser, so nothing too exciting there. (As an aside, it also runs in roc-ray.)

Steve Howell (Oct 25 2026 at 18:03):

Most people have no reason to ever run Roc on a unikernel, and that includes me to some degree, but if you're still reading, you are probably at least intrigued by the possibility of doing it.

My pure-zig unikernel actually runs on a Digital Ocean droplet running a Linux hypervisor but no actual Linux distribution. It runs right on the metal, so I literally load a "base image" on to my droplet. I don't have any shell support in the unikernel, but you can use my programming language called Shale to run little programs to walk the file system--you do it by sending a signed version of the Shale script to a web endpoint. See #off topic > shale programming language for more details.

Steve Howell (Oct 25 2026 at 18:05):

The nice about zig-webbox/roc-webbox is that you can run webbox apps on either Linux or the unikernel. The apps are extensively tested to make sure that they behave the same on Linux as in the unikernel. On Linux, you're using the real standard library zig I/O code. On the unikernel, you're using custom stacks for TCP and FAT.

Steve Howell (Oct 25 2026 at 18:08):

The unikernel is mostly single-threaded, so all your web endpoints need to be quick-running on the single-CPU droplet. You can have up to 256 TCP connections, and you can set up small jobs to run between we requests.

Steve Howell (Oct 25 2026 at 18:09):

Even in unikernel mode, you're still using the HTTP server from zig's standard library--it just swaps in the unikernel's own IO library.

Steve Howell (Oct 25 2026 at 18:11):

The TODO app itself is just vanilla HTML/JS on the client. The server persists the TODO data to the file system as one JSON file per user.

Steve Howell (Oct 25 2026 at 18:37):

## THE WEBBOX PLATFORM: a Roc app answers a web request, and its Zig host is
## a webbox site (src/roc_site.zig). The app provides `handle!`, which the
## host calls as `roc_handle` for each request it routes to Roc; the app's
## effects are hosted functions (File.roc), which the host performs as they
## are called, through webbox's store, the same on every webbox host.
platform ""
    requires {
        handle! : Http.Request => Http.Response
    }
    exposes [File, Http]
    packages {}
    provides { "roc_handle": handle_for_host! }
    hosted {
        "roc_file_read": File.read_raw!,
        "roc_file_write": File.write_raw!,
        "roc_file_delete": File.delete_raw!,
    }
    targets: {
        x64musl: {
            inputs: [app],
            output: Archive,
        },
        x64v1elf: {
            inputs: [app],
            output: Archive,
        },
        wasm32: {
            inputs: [app],
            output: Archive,
        },
    }

import File
import Http

handle_for_host! : Http.Request => Http.Response
handle_for_host! = |request| handle!(request)

Steve Howell (Oct 25 2026 at 19:33):

It's running on the same "bare metal", but it's mostly a client-side app, and the platform story is a little messier there. But it does demonstrate the unikernel can run multiple apps.

Steve Howell (Oct 26 2026 at 03:03):

The one problem with my unikernel is that it's built in zig. The zig community totally excludes people from their community who choose to build with LLMs. So with everything that I build with zig, I'm kinda on my own.

Zak Kohler (Oct 26 2026 at 11:43):

notramo (Oct 26 2026 at 11:49):

Is it about questions regarding Zig or OS dev? Or design advice? Or project contributions?

Steve Howell (Oct 26 2026 at 11:59):

Thanks, Zak! I would love for folks to play around with it. It's all the power of Claude. :)

Notification Bot (Oct 26 2026 at 12:49):

Karakatiza (Oct 27 2026 at 08:34):

TIL about unikernel. Sounds really cool, great you got it working as a platform!