Quickly Create a VirtualBox Build-Slave for Nix

Before Proceeding: A Better Way

The technique used by this repo works pretty well, but if you are able to install Docker you can get a NixOS build slave much more easily with this script. Just run:

source <(curl -fsSL https://raw.githubusercontent.com/LnL7/nix-docker/master/start-docker-nix-build-slave)

Note that this does not work on Windows.

If You Don't Want to Use Docker

This repository provides a script that can be used to easily create a NixOS build slave for your needs depending only on Nix and VirtualBox. This is useful where you're trying to deploy to a NixOS system from a non-NixOS host (e.g. using NixOps on macOS).

Prerequisites: You are not running on Windows and have VirtualBox installed.

Run . ./setup to setup your current shell. This will do the following:

1. Create a nixops VirtualBox deployment for the build-slave.
2. Deploy the build-slave.
3. Create a remote-systems.conf file that tells nix how to SSH into this machine.
4. Configure NIX_REMOTE_SYSTEMS to use this remote-systems.conf.

After running this, you should be able to use nixops as normal and it will use your build slave.

To shut-down the build-slave, run . ./shutdown which will turn off the VM and unset the environment variables.

Troubleshooting

nixops can't connect to the virtual machine via SSH. (Note that the setup script attempts to mitigate this problem.) It's not uncommon for VirtualBox to assign a new IP to virtual machines after they've been rebooted, etc. When this happens, nixops often tries to connect with the old IP and fails. (If you've deployed another virtual machine since then, it may have stolen the old IP. In this case nixops may complain that the SSH keys are not correct.) This is a known issue in nixops. The fix is to remove the old IPs from your ~/.ssh/known_hosts file and try the task again.

The scripts stopped working completely. This can happen if you did a major update to VirtualBox or modified/deleted the VirtualBox machine associated with the build-slave. You can use nixops to start everything from scratch:

nix-shell -p nixops  # Start a shell with nixops in the PATH
nixops destroy -d build-slave-vbox
nixops delete -d build-slave-vbox

Now you should be able to run the scripts and have everything start fresh.