blog.liw.fi → posts → 2025 → callisto: free, experimental CI server, initially for Rust projects

I develop CI systems as a hobby and for work. I want to gain experience in running what I've built, by running a service for others. I've set up a Radicle CI instance with my Ambient engine to run CI for open source Rust projects that have a Radicle repository. See callisto.liw.fi.

The offer:

My server runs CI for your project for free. You get feedback on whether your project builds, and its test suite runs successfully. If you can and want to, you tell me what you think of Ambient and Radicle CI. I find out if my CI system works for other people's projects and learn about missing features and other problems.

The idea is that you do me a favor and I do you a favor. In the best case we both benefit. In the worst case you waste a small amount of time and effort to try a new system.

I can't promise much, but I intend to keep this running for at least until the end of the year.

Some constraints:

  • For ideological reasons, this offer is only open to open source projects.
  • For technical reasons, your project must be in a Radicle repository and must be a Rust program. Radicle is how Ambient is notified that something is changed and that CI needs to run. Rust is required because Ambient downloads dependencies, and that is so far only implemented for Rust.
  • You get pass/fail status and a log for each run.
  • You don't get build artifacts. There is no delivery or deployment available. For now, I don't want to provide a service that publishes arbitrary files or that can access other servers. My server contains no secrets and has no access to anywhere else.

Some caveats:

  • Ambient is not mature software. It is not polished at all. It's a hobby project. User visible behavior in Ambient may change without warning. I try to avoid breaking anything, of course.
  • When I update software on the server, CI runs in progress may be terminated. Sorry. You can trigger a new run.
  • Counter caveat: I've been using Radicle with Ambient as my only CI system for most of this year so it's probably not entirely useless, maybe, possibly, I hope, but this experiment is to find out.
  • The CI server is configured so it will run when the default branch of the Radicle repository changes or when a Radicle "patch" is created or modified. A patch corresponds to a PR or MR.
  • CI runs in a virtual machine with no network access. The operating system is Debian 12 (bookworm), using CPU architecture amd64, with several Rust versions installed, with 2 virtual CPUs, 12 GiB RAM, a few tens of GB of disk space, about 30 GB of cache, and a maximum run time of 20 minutes. If these limits aren't enough, I may be able to accommodate special requests, but I'm trying to have little variation between CI projects for now.
  • Rust crate dependencies are downloaded before the VM starts and provided in the VM in /workspace/deps. If you need other dependencies that aren't in the VM, I'm going to say "sorry" for now.
  • The lack of network access is part of the security design of Ambient.
  • The server and service may go away at any time. This offer is an experiment and if I deem the experiment not worth continuing, I will terminate the service. Possibly without notice.
  • I may need to remove data and projects the server at any time, because hardware resources are limited. This might happen without warning.
  • I may need to wipe the server and re-install it from scratch, to recover from bad mistakes on my part. This too may happen without warning.
  • The above has a lot of warnings, sorry. I'm trying to manage expectations.

Selection process:

  • If you'd like your open source Rust project to use my server, post a message on the fediverse mentioning me (@liw@toot.liw.fi) with a short explanation of your project, and a link to its public Git repository. You can also email me (liw@liw.fi). If the repository is already in a Radicle repository, tell me the repository ID. You can create a Radicle repository after I tell you I'd like to select your project, if you prefer to wait.
  • I select some number of projects using nebulous and selfish criteria and add your repository to my CI server node and you can watch https://callisto.liw.fi/ for run information, including run logs. I'm likely to select all projects that seem benign, while the server has spare capacity.

Communication:

  • You follow me on the fediverse to get updates, or follow my blog. You can send me a direct message or email, if you prefer, while the experiment is running.
  • The Radicle Zulip chat system is also available, if you're willing to create an account. See the #radicle-ci channel there.

Documentation: